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Search Items: SKEWED/ INACTIVATION /MUSCULAR AND ENGLISH ONLY
1: J Neurol 2001 Oct;248(10):856-60
Clinical features and skewed X-chromosome inactivation in female carriers of
X-linked recessive spinal and bulbar muscular atrophy.
Ishihara H, Kanda F, Nishio H, Sumino K, Chihara K.
Department of Medicine, Kobe University School of Medicine, Japan.
In X-linked recessive disorders, a few female gene carriers become symptomatic.
Recent evidence implicates skewed X-chromosome inactivation in such female
carriers. We studied the clinical features of eight female gene carriers of
X-linked recessive spinal and bulbar muscular atrophy (SBMA), and evaluated the
relationship between phenotype and genotype from the viewpoint of X-chromosome
inactivation. Seven of eight cases were symptomatic, showing mild muscle
weakness, frequent muscle cramps, slight elevation of the serum creatinine
kinase level, or neurogenic changes on the electromyogram. Only one carrier was
asymptomatic clinically. For the estimation of X-chromosome inactivation, the
methylation status of the androgen receptor (AR) gene was determined by
polymerase chain reaction-based assay. Highly skewed inactivation of the
affected AR gene was found in the asymptomatic carrier, while symptomatic
carriers had a random or lower inactivation pattern of the affected AR gene.
These findings suggest that most female carriers of SBMA show some clinical
abnormalities, and highly skewed inactivation of the affected X-chromosome seems
to closely relate with escape of the manifestation in female carriers of SBMA.
PMID: 11697521 [PubMed - indexed for MEDLINE]
2: Neuromuscul Disord 2001 Jul;11(5):494-8
Pseudo-metabolic presentation in a Duchenne muscular dystrophy symptomatic
carrier with 'de novo' duplication of dystrophin gene.
Romero NB, De Lonlay P, Llense S, Leturcq F, Touati G, Urtizberea JA, Saudubray
JM, Munnich A, Kaplan JC, Recan D.
INSERM U523 and Institut de Myologie, Hopital de la Salpetriere; 47 Boulevard de
l'Hopital, 75013, Paris, France. nb.romero@myologie.chups.jussieu.fr
We report a 6-year-old female patient presenting with a sudden and severe single
episode of rhabdomyolysis in which screening for a metabolic disorder was
negative. Four months after the episode a muscle biopsy was performed and showed
a mild pattern of necrosis/regeneration. Upon immunofluorescence, a mosaic
pattern of dystrophin deficiency was found, and in the dystrophin deficient
muscle fibres, the four proteins of the sarcoglycan complex were also lacking.
Genetic analysis showed a duplication of exons 3 to 17 on one X-chromosome of
the proband, but not on the mother's X-chromosome. A clearly skewed
X-inactivation (85% of the defective X being active) was found and is consistent
with the patient being symptomatic. To our knowledge, a spontaneous
rhabdomyolysis in a female Duchenne muscular dystrophy carrier has never been
reported.
PMID: 11404124 [PubMed - indexed for MEDLINE
3: Am J Med Genet 1999 Nov 5;87(1):86-7
Screening of the C43G mutation in the promoter region of the XIST gene in
females with highly skewed X-chromosome inactivation.
Pereira LV, Zatz M.
Publication Types:
Letter
PMID: 10528256 [PubMed - indexed for MEDLINE
4: Acta Neuropathol (Berl) 1999 Jun;97(6):657-60
Variable histological expression of dystrophinopathy in two females.
Doriguzzi C, Palmucci L, Mongini T, Chiado-Piat L, Saggiorato C, Ugo I, Hoffman
EP.
Centro per le Malattie Neuromuscolari Paolo Peirolo, Torino, Italy.
palmucci@medfarm.unito.it
We report two carriers of Xp21 muscular dystrophy with unusual clinical
manifestations and striking variability of dystrophin deficiency within the same
muscle biopsy. The first patient was a 60-year-old nun with recent onset of
cramps and proximal weakness, mimicking an acquired myopathy. Muscle biopsy
disclosed slight alterations in one sample and severe dystrophic changes in
another; dystrophin was absent in 7% fibers in the former specimen and in 60% in
the second. X inactivation was skewed with 90% cells inactivating the same X
chromosome. The second patient was a 17-year-old girl with hyperCKemia, learning
disability and a family history of X-linked muscular dystrophy. Muscle biopsy
displayed slight fiber size variability and some internal nuclei; dystrophin was
absent only in one muscle fiber. A second sample with the same morphological
features demonstrated dystrophin deficiency with mosaic distribution. The
pattern of X inactivation was normal. These cases emphasize the variability of
histopathological changes and dystrophin deficiency in Xp21 muscular dystrophy
carriers and the risk of sampling errors in muscle biopsy.
PMID: 10378386 [PubMed - indexed for MEDLINE
5: Hum Genet 1999 Mar;104(3):249-53
Skewed X-inactivation in a manifesting carrier of X-linked myotubular myopathy
and in her non-manifesting carrier mother.
Tanner SM, Orstavik KH, Kristiansen M, Lev D, Lerman-Sagie T, Sadeh M,
Liechti-Gallati S.
Department of Clinical Research, Human Molecular Genetics, Children's Hospital,
University of Berne, Switzerland. tanner-1@medctr.osu.edu
X-linked recessive myotubular myopathy (XLMTM) is a muscle disorder usually
affecting newborn males. In the majority of cases, muscle weakness and hypotonia
lead to a rapid demise at neonatal age. The responsible MTM1 gene is located in
proximal Xq28. Heterozygous carriers are described as being asymptomatic but, in
a few cases, mild facial weakness has been reported. We report a family in which
a 39-year old female showed severe progressive muscle weakness. XLMTM was
initially diagnosed in the male offspring of one of the patient's sisters. The
patient, one of her sisters, and their mother were heterozygous carriers for a
common MTM1 gene mutation. We found an extremely skewed X-inactivation pattern
in the patient and, in the opposite direction, in her non-manifesting carrier
mother, thus explaining her normal phenotype and indicating a possible
inheritance of skewed X-inactivation. Linkage analysis excluded a possible
involvement of the XIST locus at Xq13.
PMID: 10323249 [PubMed - indexed for MEDLINE
6: Am J Med Genet 1998 Dec 4;80(4):356-61
Absence of correlation between skewed X inactivation in blood and serum
creatine-kinase levels in Duchenne/Becker female carriers.
Sumita DR, Vainzof M, Campiotto S, Cerqueira AM, Canovas M, Otto PA,
Passos-Bueno MR, Zatz M.
Departamento de Biologia, Instituto de Biociencias, Universidade de Sao Paulo,
SP, Brazil.
The pattern of X inactivation in lymphocyte DNA was investigated in 107 Duchenne
muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) carriers (102
asymptomatic and 5 manifesting carriers) and 117 normal female controls of
different ages, with the aim: a) to analyze the pattern of X inactivation in
blood DNA of a large number of DMD/BMD carriers as compared to normal female
controls; b) to determine if there is a decrease in serum creatine kinase (CK)
levels with age in obligate DMD/BMD carriers; c) to determine if there is a
correlation between X-chromosome inactivation and serum CK among asymptomatic
DMD/BMD carriers of different ages or with different clinical manifestations in
symptomatic carriers. A high proportion of females showed extremely skewed X
inactivation (>90% of one X preferentially inactivated), which was almost the
same among carriers and normal controls (19 and 24%, respectively). The mean
serum CK was significantly greater among young (less than 20 years old) than adult (more than 20
years old) DMD/BMD carriers and it decreased significantly until age 20 with an
apparent stabilization afterwards. No statistically significant correlation was
found between the proportion of active X(DMD) in blood and serum CK activity in
DMD/BMD carriers although it was higher among those less than 20 years old. Our
observations suggest that highly skewed X-chromosome pattern in blood (with
preferential inactivation of the X(N) chromosome) is not enough to predict that
a young DMD carrier will develop muscular weakness.
PMID: 9856563 [PubMed - indexed for MEDLINE
7: Neuromuscul Disord 1998 Dec;8(8):585-90
Cardiac transplantation in a Duchenne muscular dystrophy carrier.
Melacini P, Fanin M, Angelini A, Pegoraro E, Livi U, Danieli GA, Hoffman EP,
Thiene G, Dalla Volta S, Angelini C.
Department of Cardiology, University of Padua, Italy.
We report here for the first time the case of a symptomatic DMD carrier, who had
a heart transplant for a severe dilated cardiomyopathy. Dystrophin
immunohistochemistry, western blot and analysis of X-chromosome inactivation on
leucocytes, and skeletal and cardiac muscle biopsies on the explanted heart were
performed. The patient was a heterozygote for exons 50-52 deletion in the
dystrophin gene. The number of dystrophin-deficient fibres in the heart was much
higher than in skeletal muscle. On the other hand, the explanted heart showed a
non-skewed pattern of X-chromosome inactivation, as in leukocytes and skeletal
muscle. The adverse cardiac course may be explained by the absence of
regeneration among cardiomyocytes.
PMID: 10093066 [PubMed - indexed for MEDLINE
8: Am J Hum Genet 1998 Nov;63(5):1457-63
X chromosome inactivation in carriers of Barth syndrome.
Orstavik KH, Orstavik RE, Naumova AK, D'Adamo P, Gedeon A, Bolhuis PA, Barth PG,
Toniolo D.
Department of Medical Genetics, Ulleval University Hospital, Oslo, Norway.
k.h.orstavik@ioks.uio.no
Barth syndrome (BTHS) is a rare X-linked recessive disorder characterized by
cardiac and skeletal myopathy, neutropenia, and short stature. A gene for BTHS,
G4.5, was recently cloned and encodes several novel proteins, named "tafazzins."
Unique mutations have been found. No correlation between the location or type of
mutation and the phenotype of BTHS has been found. Female carriers of BTHS seem
to be healthy. This could be due to a selection against cells that have the
mutant allele on the active X chromosome. We therefore analyzed X chromosome
inactivation in 16 obligate carriers of BTHS, from six families, using PCR in
the androgen-receptor locus. An extremely skewed X-inactivation pattern
(>=95:5), not found in 148 female controls, was found in six carriers. The
skewed pattern in two carriers from one family was confirmed in DNA from
cultured fibroblasts. Five carriers from two families had a skewed pattern
(80:20-<95:5), a pattern that was found in only 11 of 148 female controls. Of
the 11 carriers with a skewed pattern, the parental origin of the inactive X
chromosome was maternal in all seven cases for which this could be determined.
In two families, carriers with an extremely skewed pattern and carriers with a
random pattern were found. The skewed X inactivation in 11 of 16 carriers is
probably the result of a selection against cells with the mutated gene on the
active X chromosome. Since BTHS also shows great clinical variation within
families, additional factors are likely to influence the expression of the
phenotype. Such factors may also influence the selection mechanism in carriers.
PMID: 9792874 [PubMed - indexed for MEDLINE
9: Hum Mol Genet 1998 May;7(5):855-64
Mutations in Emery-Dreifuss muscular dystrophy and their effects on emerin
protein expression.
Manilal S, Recan D, Sewry CA, Hoeltzenbein M, Llense S, Leturcq F, Deburgrave N,
Barbot J, Man N, Muntoni F, Wehnert M, Kaplan J, Morris GE.
MRIC Biochemistry Group, NE Wales Institute, Wrexham LL11 2AW, UK.
Seventeen families with Emery-Dreifuss muscular dystrophy (EDMD) have been
studied both by DNA sequencing and by emerin protein expression. Fourteen had
mutations in the X-linked emerin gene, while three showed evidence of autosomal
inheritance. Twelve of the 14 emerin mutations caused early termination of
translation. An in-frame deletion of six amino acids from the C-terminal
transmembrane helix caused almost complete absence of emerin from muscle with no
localization to the nuclear membrane, although mRNA levels were normal. This
shows that mutant emerin proteins are unstable if they are unable to integrate
into a membrane. A 22 bp deletion in the promoter region was expected to result
in reduced emerin production, but normal amounts of emerin of normal size were
found in leucocytes and lymphoblastoid cell lines. This shows that DNA analysis
is necessary to exclude emerin mutations in suspected X-linked EDMD. Emerin
levels in female carriers often deviated from the expected 50% and this was due,
in at least two families, to skewed emerin mRNA expression from the normal and
mutated alleles. In one family with a novel deletion of the last three exons of
the emerin gene, a carrier had a cardiomyopathy and very low emerin levels (<5%
of normal) due to skewed X-inactivation. In the three autosomal cases of EDMD,
emerin was normal on western blots of blood cells, which suggests that autosomal
EDMD is not caused by indirect reduction of emerin levels.
PMID: 9536090 [PubMed - indexed for MEDLINE
10: Clin Genet 1998 Feb;53(2):102-7
Skewed X inactivation in manifesting carriers of Duchenne muscular dystrophy.
Yoshioka M, Yorifuji T, Mituyoshi I.
Department of Pediatrics, Kobe General Hospital, Japan.
We studied X inactivation patterns in manifesting carriers of familial and
sporadic Duchenne muscular dystrophy (DMD) or unaffected carriers of DMD by
analysis of the methylation of HpaII sites in the first exon of the human
androgen-receptor gene (HUMARA) from peripheral blood samples. Three of the four
manifesting carriers, four of the five asymptomatic carriers, and 31 of the 32
female controls were heterozygous for the CAG repeat of HUMARA. All manifesting
carriers showed skewed X inactivation, while all unaffected carriers showed
almost symmetrical inactivation. One family studied over three generations is
noteworthy because it includes two mother/daughter pairs, one an affected pair
with skewed X inactivation, and the other a phenotypically normal carrier pair
with random X inactivation. On the other hand, the extent of X inactivation for
each X chromosome in 31 female controls was widely distributed. These data
suggest that in carriers of DMD, both affected and unaffected, it is valuable to
analyze the pattern of skewed X inactivation because it provides important
prognostic information. Carriers of DMD with skewed X inactivation might show
slowly progressive myopathy with advancing age.
PMID: 9611069 [PubMed - indexed for MEDLINE
11: Am J Hum Genet 1997 Jul;61(1):160-70
Comment in:
Am J Hum Genet. 1998 Jun;62(6):1555-7; discussion 1557-8.
Familial skewed X inactivation: a molecular trait associated with high
spontaneous-abortion rate maps to Xq28.
Pegoraro E, Whitaker J, Mowery-Rushton P, Surti U, Lanasa M, Hoffman EP.
Department of Molecular Genetics and Biochemistry, University of Pittsburgh
School of Medicine, PA 15261, USA.
We report a family ascertained for molecular diagnosis of muscular dystrophy in
a young girl, in which preferential activation (> or = 95% of cells) of the
paternal X chromosome was seen in both the proband and her mother. To determine
the molecular basis for skewed X inactivation, we studied X-inactivation
patterns in peripheral blood and/or oral mucosal cells from 50 members of this
family and from a cohort of normal females. We found excellent concordance
between X-inactivation patterns in blood and oral mucosal cell nuclei in all
females. Of the 50 female pedigree members studied, 16 showed preferential use
(> or = 95% cells) of the paternal X chromosome; none of 62 randomly selected
females showed similarly skewed X inactivation was maternally inherited in this
family. A linkage study using the molecular trait of skewed X inactivation as
the scored phenotype localized this trait to Xq28 (DXS1108; maximum LOD score
[Zmax] = 4.34, recombination fraction [theta] = 0). Both genotyping of
additional markers and FISH of a YAC probe in Xq28 showed a deletion spanning
from intron 22 of the factor VIII gene to DXS115-3. This deletion completely
cosegregated with the trait (Zmax = 6.92, theta = 0). Comparison of clinical
findings between affected and unaffected females in the 50-member pedigree
showed a statistically significant increase in spontaneous-abortion rate in the
females carrying the trait (P < .02). To our knowledge, this is the first
gene-mapping study of abnormalities of X-inactivation patterns and is the first
association of a specific locus for recurrent spontaneous abortion in a
cytogenetically normal family. The involvement of this locus in cell lethality,
cell-growth disadvantage, developmental abnormalities, or the X-inactivation
process is discussed.
PMID: 9245997 [PubMed - indexed for MEDLINE
12: Am J Hum Genet 1997 Jan;60(1):160-5
Uniparental disomy of the entire X chromosome in a female with Duchenne muscular
dystrophy.
Quan F, Janas J, Toth-Fejel S, Johnson DB, Wolford JK, Popovich BW.
DNA Diagnostic Laboratory, Oregon Health Sciences University, Portland 97201,
USA.
Duchenne muscular dystrophy (DMD) is a severe, progressive, X-linked
muscle-wasting disorder with an incidence of approximately 1/3,500 male births.
Females are also affected, in rare instances. The manifestation of mild to
severe symptoms in female carriers of dystrophin mutations is often the result
of the preferential inactivation of the X chromosome carrying the normal
dystrophin gene. The severity of the symptoms is dependent on the proportion of
cells that have inactivated the normal X chromosome. A skewed pattern of X
inactivation is also responsible for the clinical manifestation of DMD in
females carrying X;autosome translocations, which disrupt the dystrophin gene.
DMD may also be observed in females with Turner syndrome (45,X), if the
remaining X chromosome carries a DMD mutation. We report here the case of a
karyotypically normal female affected with DMD as a result of homozygosity for a
deletion of exon 50 of the dystrophin gene. PCR analysis of microsatellite
markers spanning the length of the X chromosome demonstrated that homozygosity
for the dystrophin gene mutation was caused by maternal isodisomy for the entire
X chromosome. This finding demonstrates that uniparental isodisomy of the X
chromosome is an additional mechanism for the expression of X-linked recessive
disorders. The proband's clinical presentation is consistent with the absence of
imprinted genes (i.e., genes that are selectively expressed based on the parent
of origin) on the X chromosome.
PMID: 8981959 [PubMed - indexed for MEDLINE
13: J Cell Biochem Suppl 1996;25:29-36
Cancer risk factors for selecting cohorts for large-scale chemoprevention
trials.
Greenwald P.
Division of Cancer Prevention and Control, National Cancer Institute, National
Institutes of Health, Bethesda, Maryland 20892, USA. GreenwaP@DCPC31.NCI.NIH.GOV
Many anticipate that application of findings in molecular genetics will help to
achieve greater precision in defining high-risk populations that may benefit
from chemopreventive interventions. We must recognize, however, that genetic
susceptibility, environmental factors, and complex gene-environment interactions
are all likely to be risk determinants for most cancers. Cohort studies of twins
and cancer indicate that having "identical" genes is generally not a very
accurate predictor of cancer incidence. Data from twin studies support the
suggestion that environmental factors such as tobacco use significantly
influence cancer risk. The complexities of the genetic contribution to disease
risk are exemplified by the development of Duchenne muscular dystrophy in only
one of monozygotic twin girls, hypothesized to be the result of X chromosome
inactivation, with the distribution patterns of the X chromosome being skewed to
the female X in the manifesting twin and to the male X in the normal twin.
Evidence from transgenic and genetic-environmental studies in animals support
the possibility of genetic-environmental interactions. Calorie restriction
modifies tumor expression in p53 knockout mice; a high-fat, low-calcium,
low-vitamin D diet increases prepolyp hyperplasia formation in Apc-mutated mice;
and calorie restriction early in life influences development of obesity in the
genetically obese Zucker rat (fafa). Such environmental modulation of gene
expression suggests that chemoprevention has the potential to reduce risk for
both environmentally and genetically determined cancers. In view of the growing
research efforts in chemoprevention, the NCI has developed a Prevention Trials
Decision Network (PTDN) to formalize the evaluation and approval process for
large-scale chemoprevention trials. The PTDN addresses large trial
prioritization and the associated issues of minority recruitment and retention;
identification and validation of biomarkers as intermediate endpoints for
cancer; and chemopreventive agent selection and development. A comprehensive
database is being established to support the PTDN's decision-making process and
will help to determine which agents investigated in preclinical and early phase
clinical trials should move to large-scale testing. Cohorts for large-scale
chemoprevention trials include individuals who are determined to be at high risk
as a result of genetic predisposition, carcinogenic exposure, or the presence of
biomarkers indicative of increased risk. Current large-scale trials in
well-defined, high-risk populations include the Breast Cancer Prevention Trial
(tamoxifen), the Prostate Cancer Prevention Trial (finasteride), and the
N-(4-hydroxyphenyl) retinamide (4-HPR) breast cancer prevention study being
conducted in Milan. Biomarker studies will provide valuable information for
refining the design and facilitating the implementation of future large-scale
trials. For example, potential biomarkers are being assessed at biopsy in women
with ductal carcinoma in situ (DCIS). The women are then randomized to either
placebo, tamoxifen, 4-HPR, or tamoxifen plus 4-HPR for 2-4 weeks, at which time
surgery is performed and the biomarkers reassessed to determine biomarker
modulation by the interventions. For prostate cancer, modulation of prostatic
intraepithelial neoplasia (PIN) by 4-HPR and difluoromethylornithine is being
investigated; similar studies are being planned for oltipraz,
dehydroepiandrosterone, and vitamin E plus selenomethionine. The validation of
biomarkers as surrogate endpoints for cancer incidence in high-risk cohorts will
allow more agents to be evaluated in shorter studies that use fewer subjects to
achieve the desired statistical power.
Publication Types:
Review
Review, Tutorial
PMID: 9027595 [PubMed - indexed for MEDLINE
14: Hum Genet 1995 Aug;96(2):167-76
X-chromosome methylation in manifesting and healthy carriers of
dystrophinopathies: concordance of activation ratios among first degree female
relatives and skewed inactivation as cause of the affected phenotypes.
Azofeifa J, Voit T, Hubner C, Cremer M.
Institut fur Humangenetik und Anthropologie, Universitat Heidelberg, Germany.
The X-chromosome activity states of 11 manifesting carriers of
dystrophinopathies, all with normal karyotypes, were estimated by restriction
fragment length polymorphism (RFLP)-methylation analysis with the probes M27
beta (DXS255), p2-19(DXS605) and pSPT/PGK (PGK1) to test the role of skewed
X-inactivation ratios as the cause of their affected phenotypes. In eight cases
preferential inactivation of the putative X chromosome carrying the normal
dystrophin allele in > or = 90% of their peripheral lymphocytes was observed,
two cases showed non-apparent deviant ratios (60:40 and 70:30) from the
theoretically expected values around the mean of 50% and in one case the three
markers employed yielded no information. The analysis of the X-inactivation
ratio in six mother-daughter pairs, all non-manifesting Duchenne muscular
dystrophy (DMD) carriers, and in the close female relatives of the patients
showed: (a) neither of the two X chromosomes was preferentially inactivated with
respect to their parental origin; (b) a high concordance among the activation
ratios of mothers and daughters, a result difficult to explain just in terms of
random X-chromosome inactivation.
PMID: 7635465 [PubMed - indexed for MEDLINE]
15: Neurology 1995 Apr;45(4):677-90
Comment in:
Neurology. 1996 Apr;46(4):1189-91.
Genetic and biochemical normalization in female carriers of Duchenne muscular
dystrophy: evidence for failure of dystrophin production in dystrophin-competent
myonuclei.
Pegoraro E, Schimke RN, Garcia C, Stern H, Cadaldini M, Angelini C, Barbosa E,
Carroll J, Marks WA, Neville HE.
Department of Molecular Genetics, University of Pittsburgh School of Medicine,
PA 15216, USA.
We studied 19 symptomatic female carriers of the Duchenne muscular dystrophy
(DMD) gene. Most of these dystrophinopathy patients had had an erroneous or
ambiguous diagnosis prior to dystrophin immunofluorescence testing. We assessed
clinical severity by a standardized protocol, measured X-chromosome inactivation
patterns in blood and muscle DNA, and quantitated the dystrophin protein content
of muscle. We found that patients could be separated into two groups: those
showing equal numbers of normal and mutant dystrophin genes in peripheral blood
DNA ("random" X-inactivation), and those showing preferential use of the mutant
dystrophin gene ("skewed" X-inactivation). In the random X-inactivation
carriers, the clinical phenotype ranged from asymptomatic to mild disability,
the dystrophin content of muscle was > 60% of normal, and there were only minor
histopathologic changes. In the skewed X-inactivation patients, clinical
manifestations ranged from mild to severe, but the patients with mild disease
were young (5 to 10 years old). The low levels of dystrophin (< 30% on average)
and the severe symptoms of the older patients suggested a poor prognosis for
those with skewed X-inactivation, and they all showed morphologic changes of
dystrophy. The random inactivation patients showed evidence of biochemical
"normalization," with higher dystrophin content in muscle than predicted by the
number of normal dystrophin genes. Seventy-nine percent of skewed X-inactivation
patients (11/14) showed genetic "normalization," with proportionally more
dystrophin-positive nuclei in muscle than in blood. In 65% of the skewed
X-inactivation patients, dystrophin was not produced by dystrophin-positive
nuclei; an average of 20% of myofiber nuclei were genetically
dystrophin-positive but did not produce stable dystrophin. Biochemical
normalization seems to be the main mechanism for rescue of fibers from
dystrophin deficiency in the random X-inactivation patients. In the skewed
X-inactivation patients, genetic normalization is active, but production failure
of dystrophin by dystrophin-normal nuclei may counteract any effect of
biochemical normalization. In the skewed X-inactivation patients, the remodeling
of the muscle through cycles of degeneration and regeneration led to threefold
increase in the number of dystrophin-competent nuclei in muscle myofibers (3.3
+/- 4.6), while dystrophin content was on the average 1.5-fold less then
expected (-1.54 +/- 3.38). Our results permit more accurate prognistic
assessment of isolated female dystrophinopathy patients and provide important
data with which to estimate the potential effect of gene delivery (gene therapy)
in DMD.
PMID: 7723955 [PubMed - indexed for MEDLINE
16: Am J Hum Genet 1994 Jun;54(6):989-1003
Detection of new paternal dystrophin gene mutations in isolated cases of
dystrophinopathy in females.
Pegoraro E, Schimke RN, Arahata K, Hayashi Y, Stern H, Marks H, Glasberg MR,
Carroll JE, Taber JW, Wessel HB, et al.
Department of Molecular Genetics, University of Pittsburgh, School of Medicine,
PA 15261.
Duchenne muscular dystrophy is one of the most common lethal monogenic disorders
and is caused by dystrophin deficiency. The disease is transmitted as an
X-linked recessive trait; however, recent biochemical and clinical studies have
shown that many girls and women with a primary myopathy have an underlying
dystrophinopathy, despite a negative family history for Duchenne dystrophy.
These isolated female dystrophinopathy patients carried ambiguous diagnoses with
presumed autosomal recessive inheritance (limb-girdle muscular dystrophy) prior
to biochemical detection of dystrophin abnormalities in their muscle biopsy. It
has been assumed that these female dystrophinopathy patients are heterozygous
carriers who show preferential inactivation of the X chromosome harboring the
normal dystrophin gene, although this has been shown for only a few X:autosome
translocations and for two cases of discordant monozygotic twin female carriers.
Here we study X-inactivation patterns of 13 female dystrophinopathy patients--10
isolated cases and 3 cases with a positive family history for Duchenne dystrophy
in males. We show that all cases have skewed X-inactivation patterns in
peripheral blood DNA. Of the nine isolated cases informative in our assay, eight
showed inheritance of the dystrophin gene mutation from the paternal germ line.
Only a single case showed maternal inheritance. The 10-fold higher incidence of
paternal transmission of dystrophin gene mutations in these cases is at 30-fold
variance with Bayesian predictions and gene mutation rates. Thus, our results
suggest some mechanistic interaction between new dystrophin gene mutations,
paternal inheritance, and skewed X inactivation. Our results provide both
empirical risk data and a molecular diagnostic test method, which permit genetic
counseling and prenatal diagnosis of this new category of patients.
PMID: 8198142 [PubMed - indexed for MEDLINE
17: Hum Genet 1994 May;93(5):563-7
Skewed inactivation of an X chromosome deleted at the dystrophin gene in an
asymptomatic mother and her affected daughter.
Tihy F, Vogt N, Recan D, Malfoy B, Leturcq F, Coquet M, Serville F, Fontan D,
Guillard JM, Kaplan JC, et al.
Universite de Montreal, Departement de Pathologie, Faculte de Medecine, Canada.
A girl with severe Becker muscular dystrophy and apparently normal chromosomes
had a heterozygous deletion for exons 51, 52, and 53 of the dystrophin gene.
This deletion was transmitted by her mother, who was unaffected. To
differentiate the normal and the deleted X chromosomes, fluorescence in situ
hybridization (FISH) was applied to metaphase chromosomes, using probes for both
exons 51 and 52, which are only 388 and 113 base pairs long, respectively. FISH
signals were observed in one or both chromatids of one chromosome, but never on
both chromosomes, suggesting the lack of hybridization on the deleted X
chromosome. Using 5-bromodeoxyuridine incorporation to differentiate the late
(inactive) and the early replicating (active) X chromosomes, 77% of the signals
were observed on the active X chromosomes in the mother. This percentage was
only 18% in the daughter, suggesting that skewed inactivation of the X
chromosomes was responsible for the phenotypic differences.
PMID: 8168835 [PubMed - indexed for MEDLINE
18: Am J Med Genet 1993 Mar 1;45(5):601-5
In situ hybridization shows direct evidence of skewed X inactivation in one of
monozygotic twin females manifesting Duchenne muscular dystrophy.
Zneimer SM, Schneider NR, Richards CS.
University of Texas Southwestern Medical Center, Department of Pathology,
Dallas.
A novel combination of conventional and molecular cytogenetic techniques was
used to investigate the expression of an X-linked recessive disorder in one of
monozygotic (MZ) twin females. These twins carry a deletion, approximately 300
kb in length, in one of their X chromosomes within the dystrophin gene, which is
responsible for Duchenne muscular dystrophy (DMD) in one twin [Richards et al.:
Am J Hum Genet 46:672-681, 1990]. A unique DNA fragment generated from an exon
within this gene deletion was hybridized in situ to both twins' metaphase
chromosomes, a probe which would presumably hybridize only to the normal X
chromosome and not to the X chromosome carrying the gene deletion. Chromosomes
were identified by reverse-banding (R-banding) and by the addition of
5-bromodeoxyuridine (BrdU) in culture to distinguish early and late replicating
X chromosomes, corresponding to active and inactive X chromosomes, respectively.
Hybridization experiments showed predominant inactivation of the normal X
chromosome in the twin with DMD. This is the first report showing direct
evidence at the chromosome level of unequal inactivation of cytogenetically
normal X chromosomes resulting in the manifestation of an X-linked recessive
disorder in one of monozygotic twin females. This study may now facilitate other
research of unequal X inactivation and of females manifesting X-linked recessive
disorders.
PMID: 8456832 [PubMed - indexed for MEDLINE
19: Am J Med Genet 1991 Sep 1;40(3):354-64
Discordance of muscular dystrophy in monozygotic female twins: evidence
supporting asymmetric splitting of the inner cell mass in a manifesting carrier
of Duchenne dystrophy.
Lupski JR, Garcia CA, Zoghbi HY, Hoffman EP, Fenwick RG.
Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030.
In 1990, Richards et al. reported dramatically skewed lyonization in a set of
female monozygotic twins heterozygous for Duchenne muscular dystrophy (DMD). The
skewed inactivation pattern was symmetrical in opposite directions, one twin
being affected with DMD, the other one being normal. Here, we report an
additional set of female monozygotic twins heterozygous for a mutation at the
dystrophin locus. Similarly, one shows a manifesting carrier phenotype while one
is normal. However, unlike the previous report, we find a skewed X inactivation
pattern only in the affected twin, while the normal twin showed a random X
inactivation pattern. Our results lend considerable experimental support for the
models of twinning and X inactivation recently outlined by Nance in 1990, in
that these twins probably represent asymmetric splitting of the inner cell mass
(ICM): The affected twin likely arose when a small proportion of the ICM split
off after lyonization had occurred. In this situation, the original ICM could
give rise to the normal twin with random lyonization, while the newly split
cells would experience catch-up growth and lead to the affected twin. Genetic
studies of this family showed that the specific dystrophin gene mutation was an
exon duplication that arose sporadically in the paternally derived X chromosome.
PMID: 1683155 [PubMed - indexed for MEDLINE
20: Am J Hum Genet 1990 Apr;46(4):672-81
Skewed X inactivation in a female MZ twin results in Duchenne muscular
dystrophy.
Richards CS, Watkins SC, Hoffman EP, Schneider NR, Milsark IW, Katz KS, Cook JD,
Kunkel LM, Cortada JM.
GeneScreen, Department of Pediatrics, University of Texas Southwestern Medical
Center, Dallas 75207.
One of female MZ twins presented with muscular dystrophy. Physical examination,
creatine phosphokinase levels, and muscle biopsy were consistent with Duchenne
muscular dystrophy (DMD). However, because of her sex she was diagnosed as
having limb-girdle muscular dystrophy. With cDNA probes to the DMD gene, a gene
deletion was detected in the twins and their mother. The de novo mutation which
arose in the mother was shown by novel junction fragments generated by HindIII,
PstI, or TaqI when probed with cDNA8. Additional evidence of a large gene
deletion was given by novel SfiI junction fragments detected by probes p20,
J-Bir, and J-66 on pulsed-field gel electrophoresis (PFGE). Immunoblot analysis
of muscle from the affected twin showed dystrophin of normal size but of reduced
amount. Immunofluorescent visualization of dystrophin revealed foci of
dystrophin-positive fibers adjacent to foci of dystrophin-negative fibers. These
data indicate that the affected twin is a manifesting carrier of an abnormal DMD
gene, her myopathy being a direct result of underexpression of dystrophin.
Cytogenetic analysis revealed normal karyotypes, eliminating the possibility of
a translocation affecting DMD gene function. Both linkage analysis and DNA
fingerprint analysis revealed that each twin has two different X chromosomes,
eliminating the possibility of uniparental disomy as a mechanism for DMD
expression. On the basis of methylation differences of the paternal and maternal
X chromosomes in these MZ twins, we propose uneven lyonization (X chromosome
inactivation) as the underlying mechanism for disease expression in the affected
female.
PMID: 2180286 [PubMed - indexed for MEDLINE]
Mail Bill: btillier@shaw.ca
.