Skewed X-inactivation Pattern Research Articles

Multiple Congenital Anomalies-Hypotonia-Seizures Syndrome 2 Caused by a Novel PIGA Variant Not Associated with a Skewed X-Inactivation Pattern

Germline variants in the phosphatidylinositol glycan class A (PIGA) gene, which is involved in glycosylphosphatidylinositol (GPI) biosynthesis, cause multiple congenital anomalies-hypotonia-seizures syndrome 2 (MCAHS2) with X-linked recessive inheritance. The available literature has described a pattern of almost 100% X-chromosome inactivation in mothers carrying PIGA variants. Here, we report a male infant with MCAHS2 caused by a novel PIGA variant inherited from his mother, who has a non-skewed pattern of X inactivation. Phenotypic evidence supporting the pathogenicity of the variant was obtained by flow-cytometry tests. We propose that the assessment in neutrophils of the expression of GPI-anchored proteins (GPI-APs), especially CD16, should be considered in cases with variants of unknown significance with random X-inactivation in carrier mothers in order to clarify the pathogenic role of PIGA or other gene variants linked to the synthesis of GPI-APs.

Fine Breakpoint Mapping by Genome Sequencing Reveals the First Large X Inversion Disrupting the NHS Gene in a Patient with Syndromic Cataracts

Inversions are structural variants that are generally balanced. However, they could lead to gene disruptions or have positional effects leading to diseases. Mutations in the NHS gene cause Nance-Horan syndrome, an X-linked disorder characterised by congenital cataracts and dental anomalies. Here, we aimed to characterise a balanced pericentric inversion X(p22q27), maternally inherited, in a child with syndromic bilateral cataracts by breakpoint mapping using whole-genome sequencing (WGS). 30× Illumina paired-end WGS was performed in the proband, and breakpoints were confirmed by Sanger sequencing. EdU assays and FISH analysis were used to assess skewed X-inactivation patterns. RNA expression of involved genes in the breakpoint boundaries was evaluated by droplet-digital PCR. We defined the breakpoint position of the inversion at Xp22.13, with a 15 bp deletion, disrupting the unusually large intron 1 of the canonical NHS isoform, and also perturbing topologically-associated domains (TADs). Moreover, a microhomology region of 5 bp was found on both sides. RNA analysis confirmed null and reduced NHS expression in the proband and his unaffected mother, respectively. In conclusion, we report the first chromosomal inversion disrupting NHS, fine-mapped by WGS. Our data expand the clinical spectrum and the pathogenic mechanisms underlying the NHS defects.

Intelligence Quotient Variability in Klinefelter Syndrome Is Associated With GTPBP6 Expression Under Regulation of X-Chromosome Inactivation Pattern

Klinefelter syndrome (KS) displays a broad dysmorphological, endocrinological, and neuropsychological clinical spectrum. We hypothesized that the neurocognitive dysfunction present in KS relies on an imbalance in X-chromosome gene expression. Thus, the X-chromosome inactivation (XCI) pattern and neurocognitive X-linked gene expression were tested and correlated with intelligence quotient (IQ) scores. We evaluated 11 KS patients by (a) IQ assessment, (b) analyzing the XCI patterns using both HUMARA and ZDHHC15 gene assays, and (c) blood RT-qPCR to investigate seven X-linked genes related to neurocognitive development (GTPBP6, EIF2S3, ITM2A, HUWE1, KDM5C, GDI1, and VAMP7) and XIST in comparison with 14 (male and female) controls. Considering IQ 80 as the standard minimum reference, we verified that the variability in IQ scores in KS patients seemed to be associated with the XCI pattern. Seven individuals in the KS group presented a random X-inactivation (RXI) and lower average IQ than the four individuals who presented a skewed X-inactivation (SXI) pattern. The evaluation of gene expression showed higher GTPBP6 expression in KS patients with RXI than in controls (p = 0.0059). Interestingly, the expression of GTPBP6 in KS patients with SXI did not differ from that observed in controls. Therefore, our data suggest for the first time that GTPBP6 expression is negatively associated with full-scale IQ under the regulation of the type of XCI pattern. The SXI pattern may regulate GTPBP6 expression, thereby dampening the impairment in cognitive performance and playing a role in intelligence variability in individuals with KS, which warrants further mechanistic investigations.

Severe syndromic ID and skewed X-inactivation in a girl with NAA10 dysfunction and a novel heterozygous de novo NAA10 p.(His16Pro) variant - a case report

BackgroundNAA10 is the catalytic subunit of the major N-terminal acetyltransferase complex NatA which acetylates almost half the human proteome. Over the past decade, many NAA10 missense variants have been reported as causative of genetic disease in humans. Individuals harboring NAA10 variants often display variable degrees of intellectual disability (ID), developmental delay, and cardiac anomalies. Initially, carrier females appeared to be oligo- or asymptomatic with X-inactivation pattern skewed towards the wild type allele. However, recently it has been shown that NAA10 variants can cause syndromic or non-syndromic intellectual disability in females as well. The impact of specific NAA10 variants and the X-inactivation pattern on the individual phenotype in females remains to be elucidated.Case presentationHere we present a novel de novo NAA10 (NM_003491.3) c.[47A > C];[=] (p.[His16Pro];[=]) variant identified in a young female. The 10-year-old girl has severely delayed motor and language development, disturbed behavior with hyperactivity and restlessness, moderate dilatation of the ventricular system and extracerebral CSF spaces. Her blood leukocyte X-inactivation pattern was skewed (95/5) towards the maternally inherited X-chromosome. Our functional study indicates that NAA10 p.(H16P) impairs NatA complex formation and NatA catalytic activity, while monomeric NAA10 catalytic activity appears to be intact. Furthermore, cycloheximide experiments show that the NAA10 H16P variant does not affect the cellular stability of NAA10.Discussion and conclusionsWe demonstrate that NAA10 p.(His16Pro) causes a severe form of syndromic ID in a girl most likely through impaired NatA-mediated Nt-acetylation of cellular proteins. X-inactivation analyses showed a skewed X-inactivation pattern in DNA from blood of the patient with the maternally inherited allele being preferentially methylated/inactivated.

High penetrance of EDA pathogenic variants in Mexican female carriers with hypohidrotic ectodermal dysplasia

X-linked hypohidrotic ectodermal dysplasia (XLHED) is caused by EDA pathogenic variants. Female carriers show several clinical manifestations in variable percentages. We studied 11 Mexican heterozygous females with an EDA variant. The most frequent symptoms were similar to previous reports; however, two females (18%) reported dry eye syndrome, data rarely explored in carriers. The penetrance was 91% with clinical variability that might be related to the location of the mutation and/or to a skewed X-inactivation pattern. Our results highlight the importance of offering molecular testing to potential female carriers and support XLHED as an X-linked entity with incomplete penetrance in females.

Novel clinical and genetic insight into CXorf56-associated intellectual disability

Intellectual disability (ID) is one of most frequent reasons for genetic consultation. The complex molecular anatomy of ID ranges from complete chromosomal imbalances to single nucleotide variant changes occurring de novo, with thousands of genes identified. This extreme genetic heterogeneity challenges the molecular diagnosis, which mostly requires a genomic approach. CXorf56 is largely uncharacterized and was recently proposed as a candidate ID gene based on findings in a single Dutch family. Here, we describe nine cases (six males and three females) from three unrelated families. Exome sequencing and combined database analyses, identified family-specific CXorf56 variants (NM_022101.3:c.498_503del, p.(Glu167_Glu168del) and c.303_304delCTinsACCC, p.(Phe101Leufs*20)) that segregated with the ID phenotype. These variants are presumably leading to loss-of-function, which is the proposed disease mechanism. Clinically, CXorf56-related disease is a slowly progressive neurological disorder. The phenotype is more severe in hemizygote males, but might also manifests in heterozygote females, which showed skewed X-inactivation patterns in blood. Male patients might present previously unreported neurological features such as epilepsy, abnormal gait, tremor, and clonus, which extends the clinical spectrum of the disorder. In conclusion, we confirm the causative role of variants in CXorf56 for an X-linked form of intellectual disability with additional neurological features. The gene should be considered for molecular diagnostics of patients with ID, specifically when family history is suggestive of X-linked inheritance. Further work is needed to understand the role of this gene in neurodevelopment and intellectual disability.

Altered Gene-Regulatory Function of KDM5C by a Novel Mutation Associated With Autism and Intellectual Disability.

Intellectual disability (ID) affects up to 2% of the population world-wide and often coincides with other neurological conditions such as autism spectrum disorders. Mutations in KDM5C cause Mental Retardation, X-linked, Syndromic, Claes-Jensen type (MRXSCJ, OMIM #300534) and are one of the most common causes of X-linked ID. KDM5C encodes a histone demethylase for di- and tri-methylated histone H3 lysine 4 (H3K4me2/3), which are enriched in transcriptionally engaged promoter regions. KDM5C regulates gene transcription; however, it remains unknown whether removal of H3K4me is fully responsible for KDM5C-mediated gene regulation. Most mutations functionally tested to date result in reduced enzymatic activity of KDM5C, indicating loss of demethylase function as the primary mechanism underlying MRXSCJ. Here, we report a novel KDM5C mutation, R1115H, identified in an individual displaying MRXSCJ-like symptoms. The carrier mother’s cells exhibited a highly skewed X-inactivation pattern. The KDM5C-R1115H substitution does not have an impact on enzymatic activity nor protein stability. However, when overexpressed in post-mitotic neurons, KDM5C-R1115H failed to fully suppress expression of target genes, while the mutant also affected expression of a distinct set of genes compared to KDM5C-wildtype. These results suggest that KDM5C may have non-enzymatic roles in gene regulation, and alteration of these roles contributes to MRXSCJ in this patient.

Variantes que mantienen el marco de lectura en el dominio Rod 1 proximal del gen FLNA se asocian con un predominio del fenotipo valvular

Introduction and objectivesX-linked cardiac valvular dysplasia is a rare form of male-specific congenital heart defect mainly characterized by myxomatous degeneration of the atrioventricular valves with variable hemodynamic consequences. It is caused by genetic defects in FLNA-encoded filamin A, a widely expressed actin-binding protein that regulates cytoskeleton organization. Filamin A loss of function has also been associated with often concurring neurologic and connective tissue manifestations, with mutations in the first half of the Rod 1 domain apparently expressing the full cardiac phenotype. We contribute to previous genotype-phenotype correlations with a multidisciplinary approach in a newly-described family. MethodsCardiologic, dysmorphologic, and genetic evaluation of available members were complemented with transcriptional and X-chromosome inactivation studies. ResultsA novel FLNA mutation c.1066-3C>G cosegregated with a male-expressed, apparently isolated, cardiac phenotype with no skewed X-inactivation pattern in female carriers. This variant was shown to result in an in-frame deletion of 8 amino acid residues near the N-terminal region of the protein. ConclusionsA nonimprinted, partial loss of function of filamin A proximal Rod 1 domain seems to be the pathogenetic mechanism of cardiac valvular dysplasia, with some cases occasionally expressing associated extracardiac manifestations.Full English text available from: www.revespcardiol.org/en

In-frame Variants in FLNA Proximal Rod 1 Domain Associate With a Predominant Cardiac Valvular Phenotype

Introduction and objectivesX-linked cardiac valvular dysplasia is a rare form of male-specific congenital heart defect mainly characterized by myxomatous degeneration of the atrioventricular valves with variable hemodynamic consequences. It is caused by genetic defects in FLNA-encoded filamin A, a widely expressed actin-binding protein that regulates cytoskeleton organization. Filamin A loss of function has also been associated with often concurring neurologic and connective tissue manifestations, with mutations in the first half of the Rod 1 domain apparently expressing the full cardiac phenotype. We contribute to previous genotype-phenotype correlations with a multidisciplinary approach in a newly-described family. MethodsCardiologic, dysmorphologic, and genetic evaluation of available members were complemented with transcriptional and X-chromosome inactivation studies. ResultsA novel FLNA mutation c.1066-3C>G cosegregated with a male-expressed, apparently isolated, cardiac phenotype with no skewed X-inactivation pattern in female carriers. This variant was shown to result in an in-frame deletion of 8 amino acid residues near the N-terminal region of the protein. ConclusionsA nonimprinted, partial loss of function of filamin A proximal Rod 1 domain seems to be the pathogenetic mechanism of cardiac valvular dysplasia, with some cases occasionally expressing associated extracardiac manifestations.

Identification of Intellectual Disability Genes in Female Patients with a Skewed X-Inactivation Pattern

Intellectual disability (ID) is a heterogeneous disorder with an unknown molecular etiology in many cases. Previously, X-linked ID (XLID) studies focused on males because of the hemizygous state of their X chromosome. Carrier females are generally unaffected because of the presence of a second normal allele, or inactivation of the mutant X chromosome in most of their cells (skewing). However, in female ID patients, we hypothesized that the presence of skewing of X-inactivation would be an indicator for an X chromosomal ID cause. We analyzed the X-inactivation patterns of 288 females with ID, and found that 22 (7.6%) had extreme skewing (>90%), which is significantly higher than observed in the general population (3.6%; P=0.029). Whole-exome sequencing of 19 females with extreme skewing revealed causal variants in six females in the XLID genes DDX3X, NHS, WDR45, MECP2, and SMC1A. Interestingly, variants in genes escaping X-inactivation presumably cause both XLID and skewing of X-inactivation in three of these patients. Moreover, variants likely accounting for skewing only were detected in MED12, HDAC8, and TAF9B. All tested candidate causative variants were de novo events. Hence, extreme skewing is a good indicator for the presence of X-linked variants in female patients.

Combined De-Novo Mutation and Non-Random X-Chromosome Inactivation Causing Wiskott-Aldrich Syndrome in a Female with Thrombocytopenia

Disorders linked to mutations in the X chromosomes typically affect males. The aim of the study is to decipher the mechanism of disease expression in a female patient with a heterozygous mutation on the X-chromosome. Clinical data was extracted from the Canadian Inherited Marrow Failure Registry. Genomic ribonucleic acid (DNA) and complementary DNA (cDNA) underwent Sanger sequencing. Protein analysis was performed by flow cytometry. X-inactivation patterns were analyzed by evaluating the DNA methylation status and cDNA clonal expression of several genes on the X-chromosome. SNP array was used for molecular karyotyping of the X-chromosome. A female with thrombocytopenia, eczema and mild T-lymphocyte abnormalities with extensive negative diagnostic testing, was suspected to have Wiskott-Aldrich syndrome (WAS)/X-linked thrombocytopenia. Although the girl had a mutation (c.397G > A, p.E133K) in only one allele, she was found to have an extremely skewed X-inactivation pattern and no expression of the WAS protein. Family studies using DNA methylation analysis and cDNA clonal expression of several genes on the X-chromosome demonstrated that the patient developed de-novo non-random inactivation of the X-chromosome that does not carry the mutation. Genome-wide high-density molecular karyotyping excluded deletions and amplifications as a cause for the non-random inactivation of one X-chromosome. Our study emphasizes the need to test selected female patients with complete or incomplete disease expression for X-linked disorders even in the absence of a family history.

Skewed X-inactivation patterns in ageing healthy and myelodysplastic haematopoiesis determined by a pyrosequencing based transcriptional clonality assay

BackgroundInvestigation of X-chromosome inactivation patterns (XCIP) by determination of differential CpG-methylation has been widely applied for investigation of female cell clonality. Using this approach the clonal origin of various tumours...

X-exome sequencing identifies a HDAC8 variant in a large pedigree with X-linked intellectual disability, truncal obesity, gynaecomastia, hypogonadism and unusual face

BackgroundWe present a large Dutch family with seven males affected by a novel syndrome of X-linked intellectual disability, hypogonadism, gynaecomastia, truncal obesity, short stature and recognisable craniofacial manifestations resembling but...

Duchenne Muscular Dystrophy in a 4-Year-Old Girl due to Heterozygous Frame Shift Deletion of the Dystrophin Gene and Skewed X-Inactivation

X-linked recessive diseases affect males, whereas female carriers are generally asymptomatic.We report on a 4-year-old girl who presented with a classical phenotype of Duchenne Muscular Dystrophy (DMD), a severe X-linked recessive type of muscular dystrophy affecting boys in early childhood.A thorough diagnostic work-up revealed that this resulted from a heterozygous out-of frame deletion in the DMD-gene in combination with an X-inactivation ratio of <10:90 in blood leukocytes and muscle.The case exemplifies that a skewed X-inactivation pattern has to be taken into account as mechanism causing clinical symptoms in female carriers of X-linked recessive disorders.

Autism in two females with duplications involving Xp11.22-p11.23

We present two phenotypically similar females with Xp duplication who have autism and epilepsy. Case 1 is a 14-year-old Honduran female with autism and medically refractory complex partial, secondarily generalized epilepsy. Case 2 is a 3-year-old Austrian female with autism and medically refractory complex partial epilepsy. Both patients also share features of severe intellectual disability (case 1 has a developmental quotient of 23, case 2 has a developmental quotient of 42) and dysmorphic facial features. Autism was confirmed by thorough clinical evaluations and testing. Case 1 has a karyotype of 46,X,dup(X)(p11.2-p22.33) and a highly skewed X-inactivation pattern (94:6). Brain magnetic resonance imaging (MRI) and electroencephalogram (EEG) were abnormal. Case 2 has a 5-megabase duplication of Xp11.22-p11.23 on chromosome microarray analysis. The patient has a random X-inactivation pattern (77:23). Brain MRI was normal, but EEG was abnormal. Both patients have duplications involving the Xp11.22-p11.23 region, indicating that this is an area of interest for future translational autism research.

Reply to He et al

We appreciate the comments of He et al.1 Our response is outlined below. In fact, it had been reported that HSD17B10 is a part of a multigene domain in Xp11.21–p11.22 that escapes X-inactivation.2 Later results by Carrel et al3 showed that this gene is probably subjected to X-inactivation as only one of nine hybrids escapes from it. This observation can not be inferred from Figure 2 of Yang et al,4 while the results are more clarifying in the adapted figure of the letter of He et al.1 To elucidate whether HSD17B10 cDNA doses differed between both sexes, we performed relative quantification (RQ) of wild-type HSD17B10 cDNA alleles in four female and four male controls. The results did not show any significant difference between the doses in both sexes. Therefore, these results are in favour of an X-linked disease that does not escape X-inactivation and are in agreement with the observations of Carrel et al.3 Fibroblasts were obtained from a single biopsy, as it would not have been ethical to perform additional biopsies with the only purpose of performing these studies. In fibroblasts we not only performed genetic studies but also determined enzymatic activities with good correlation between both, which gives more strength to the results. Relatively large deviations are often observed in real-time PCR quantification, owing to the low specificity of the probes and variability of the endogenous controls. However, despite these difficulties, the same expression levels in the first female patient and her brother were observed, which is in agreement with the sequencing results, the low enzymatic activity, the severe clinical presentation and the skewed X-inactivation pattern. The second female showed expression of both mutant and wild-type alleles, which is also in agreement with sequencing results, normal enzymatic activity, slight clinical presentation and random X-inactivation pattern. In conclusion, our results are adequately supported by the studies in controls and are confirmed by the studies in patients. We thank He et al for giving us the opportunity to clarify some issues, although we think that they do not change the conclusions of our study.

Skewed X-chromosome inactivation causing diagnostic misinterpretation in congenital nephrogenic diabetes insipidus

To establish the clinical phenotype and genetic background in a family with diabetes insipidus. The subjects were a sister and brother, aged 34 and 27 years, respectively, with a history of polyuria since infancy. Clinical testing confirmed a diagnosis of congenital nephrogenic diabetes insipidus (CNDI) in both. Samples of purified genomic DNA were analysed. The sequence of the entire coding region of the AQP2 gene as well as the AVPR2 gene was determined. Sequence analysis revealed no variations in the AQP2 gene. A missense variation in exon 2 of the AVPR2 gene (g.685G>A), predicting a p.Asp85Asn substitution, was identified in the X-chromosome of the affected male and one allele in the sister and the asymptomatic mother. The p.Asp85Asn variation in AVPR2 is known to cause CNDI, and has previously been described as inducing a partial phenotype treatable with dDAVP. However, in this family dDAVP had no influence on urine osmolality, whereas combination therapy with indomethacin and hydrochlorothiazide increased urine osmolality to 299 mosm/l in the proband. A skewed X-inactivation pattern (93%) occurring in the normal X allele was recognized in the sister. This study demonstrates the effect of skewed X-chromosome inactivation associated with X-linked CNDI. Polydipsia in early childhood could be due to X-linked CNDI despite affecting both genders. The significant heterogeneity in the clinical phenotype in CNDI carries a risk of diagnostic misinterpretation and emphasizes the need for genetic characterization. Treatment combining indomethacin and hydrochlorothiazide results in a marked response on both urine output and urine osmolality.

New Mutation in ALAS2 as the Cause of X-Linked Sideroblastic Anemia Responsive to Pyridoxine: Comparison of ALAS2-Defective and DMT1-Defective BFU-E Growth.

Abstract 4051Poster Board III-986Congenital sideroblastic anemias (SA) are hypochromic microcytic anemias with secondary iron overload. Local iron accumulation in mitochondria results in the formation of ringed sideroblasts in the bone marrow. Defects in heme synthesis, Fe-S cluster biogenesis and export have been reported in SA patients. X-linked sideroblastic anemia is a rare gonosomal recessive disorder, resulting from mutations in erythroid-specific delta-aminolevulinate synthase (ALAS2), the first enzyme of heme biosynthesis. It affects mostly males. Few cases of affected females, due to skewed X-inactivation pattern favoring the mutant allele have been reported. Inefficiency of ALAS2 leads to decreased heme production and ineffective erythropoiesis. We investigated a group of 4 young males (average age 28) with congenital SA. Two of the patients had family history of SA and iron overload in males corresponding with the X-linked inheritance. All the patients had hemoglobin level lower than 119 g/L, mean corpuscular volume under 71 fL, increased serum ferritin and numerous sideroblasts in their bone marrow. We performed screening of all exons and promoter region of ALAS2. One patient was negative for ALAS2 mutation, and is a candidate for SLC25A38 mutation screening which only recently has been published as the second most frequent lesion in congenital SA. In two patients we found previously published R452H and R452C mutations; a novel K156E substitution was discovered in one patient. All these three patients responded partially to high dose of pyridoxine. K156 is a conserved amino acid residue and K156E substitution is SIFT predicted as affecting the protein function (the functional study is ongoing). This mutation was not found in 40 healthy controls or 10 patients with myelodysplastic syndrome with SA (RARS, RCMD-RS). Based on our previous study with DMT-1-deficient erythroid progenitors (Priwitzerova et al. Blood 2004;103:3991-2), we also evaluated a possible erythropoietic defect of ALAS2-mutant erythroid progenitors using methylcellulose-based colony assays. We observed that the in vitro growth of all aforementioned ALAS2-mutant patient's erythroid progenitors (BFU-Es) is not affected, which is in contrast to the defective growth of DMT1-mutant erythroid progenitors. These results suggest that impaired heme synthesis is better tolerated by erythroid progenitors than general iron deficiency due to the block in erythroid iron uptake by DMT1 and that the defect in heme synthesis does not fully account for the impaired hemoglobinization and poor growth of DMT1-defective BFU-Es. These data support the role of iron in other processes involved in erythroid-colony development apart from heme synthesis. In conclusion, we present a novel K156E ALAS2 mutation leading to pyridoxine-responsive X-linked sideroblastic anemia. Using BFU-E assays we also submit that lesions in iron-dependent proteins apart from defective heme synthesis contribute to impaired erythroid colony formation in previously described DMT1-mutant erythroid progenitors.Grant support: Ministry of Health Czech Republic grants NS9935-3 and NS10281-3 and Ministry of Education, Youth and Sports program MSM 6198959205. Disclosures:No relevant conflicts of interest to declare.

CHM gene molecular analysis and X‐chromosome inactivation pattern determination in two families with choroideremia

Choroideremia is an X-linked recessive retinal dystrophy characterized by progressive loss of the photoreceptor, the retinal pigment epithelium, and the choriocapillaris layers which ultimately can result in blindness by the fifth decade of life. The disease is caused by mutations in the gene CHM, which encodes a protein involved in the regulation of intracellular vesicular traffic. Typically, hemizygous males are affected by the disease and female carriers are asymptomatic with only a diffuse mottled pattern of hyperpigmentation on funduscopy. Uncommon instances of fully affected females have been described previously and these cases are proposed to arise from an skewed Lyonization mechanism preferentially inactivating the X chromosome carrying the normal CHM allele. In this work, the clinical and molecular features of two Mexican families with choroideremia are described. A novel and a previously described CHM mutation were identified. X-chromosome inactivation assays were performed in a total of 12 heterozygous carriers from the two families. In an affected female from family A, a random X-inactivation pattern was demonstrated; on the other hand, in a female carrier from family B displaying a conspicuous pattern of pigment epithelium mottling at the peripheral retina, a skewed X-inactivation pattern was found. However, the X-chromosome preferentially inactivated in this female was the one carrying the mutated allele. Our results add to the genotypic spectrum in choroideremia and does not support a correlation between X-inactivation status and abnormal retinal phenotype in heterozygous female carriers from these two families.

Premature ovarian failure and fragile X female premutation carriers

The association between FMR1 premutation and ovarian dysfunction has been widely studied, and many factors such as the repeat tract size, the sequence organization of the CGG repeat tract, the parental origin of the premutation, and the FMR1 mRNA levels have been examined. X-chromosome inactivation has also been studied as a risk factor, but the reported results are inconclusive. Although some authors did not find an association with the premature ovarian failure manifestation, others suggest that the severity of FMR1 premutation-associated phenotypes may be related to this X-inactivation ratio. To evaluate the significance of skewed X-inactivation patterns among female premutated carriers, we examined and compared the X-inactivation ratios of 220 female samples from the general population and 260 female premutation carriers phenotypically unaffected or affected by premature ovarian failure. The results failed to show a direct effect of X-inactivation in the manifestation of premature ovarian failure among FMR1 premutation carriers. However, a negative correlation has been found between X-chromosome inactivation and low-medium CGG repeat size alleles. The manifestation of premature ovarian failure cannot be merely explained by the X-chromosome inactivation patterns; however, we speculate that together with other genetic factors, it might contribute.