Clinical Manifestation in Females with X-linked Metabolic Disorders: Genetic and Pathophysiological Considerations

Abstract Inborn errors of metabolism are predominantly autosomal-recessive disorders, but several follow an X-linked pattern of inheritance. They are called X-linked recessive, if the female carriers are asymptomatic, and are called X-linked dominant disorders, if almost all females are affected. Conditions, in which some females have symptoms while others are asymptomatic lifelong are simply referred to as X-linked. The aim of this review is to point out the variability in clinical manifestation of affected females in some X-linked metabolic disorders and to discuss on the basis of these examples possible mechanisms that may explain the broad phenotypic spectrum, such as the type of the underlying mutation, the issue of autonomous versus non-autonomous gene expression and the degree of skewing of X-inactivation. The use of the terms "X-linked dominant" and "X-linked recessive" will be discussed.

Advances in the Pathogenic Research of Female Carriers with Symptomatic Duchenne Muscular Dystrophy / 现代生物医学进展

DMD/BMD is a X-linked recessive hereditary disease.It predominantly affects males.While female carriers do not have symptoms,due to their inactive X chromosome make it present mosaic.Recently,more and more papers reported that a clinically significant proportion of DMD/BMD female carriers have symptoms.They presented variable degrees of symptoms.But the mechanism of the pathogencity is still not clear.Most of the research considered that the dominating reason is the skewed X inactivation.It means that the predominant expression of the DMD mutant allele make the normal one have weak expression,thus no function dystrophin proteins could be generate,manifested as DMD/BMD.In this paper,we mainly summarized the relationship between skewed X inactivation and pathogenicity of the symptomatic DMD female carriers.

Novel ATRX gene damaging missense mutation c.6740A>C segregates with profound to severe intellectual deficiency without alpha thalassaemia.

Background & objectives: ATRX is a recessive X-linked intellectual deficiency (X-LID) gene causing predominately alpha-thalassaemia with a wide and clinically heterogeneous spectrum of intellectual deficiency syndromes. Although alpha-thalassaemia is commonly present, some patients do not express this sign despite the ATRX gene being altered. Most pathological mutations have been localized in two different major domains, the helicase and the plant homeo-domain (PHD)-like domain. In this study we examined a family of three males having an X-linked mental deficiency and developmental delay, and tried to establish a genetic diagnosis while discussing and comparing the phenotype of our patients to those reported in the literature. Methods: Three related males with intellectual deficiency underwent clinical investigations. We performed a karyotype analysis, CGH-array, linkage study, and X-exome sequencing in the index case to identify the genetic origin of this disorder. The X-inactivation study was carried out in the mother and Sanger sequencing was achieved in all family members to confirm the mutation. Results: A novel ATRX gene missense mutation (p.His2247Pro) was identified in a family of two uncles and their nephew manifesting intellectual deficiency and specific facial features without alpha-thalassaemia. The mutation was confirmed by Sanger sequencing. It segregated with the pathological phenotype. The mother and her two daughters were found to be heterozygous. Interpretation & conclusions: The novel mutation c.6740A>C was identified within the ATRX gene helicase domain and confirmed by Sanger sequencing in the three affected males as well as in the mother and her two daughters. This mutation was predicted to be damaging and deleterious. The novel mutation segregated with the phenotype without alpha-thalassaemia and with non-skewed X chromosome.

ATR-X syndrome in two siblings with a novel mutation (c.6718C>T mutation in exon 31).

ATR-X syndrome is an X-linked mental retardation syndrome characterized by mental retardation, alpha thalassaemia and distinct facial features which include microcephaly, frontal hair upsweep, epicanthic folds, small triangular nose, midface hypoplasia and carp-shaped mouth. Here we report two brothers with clinical features of ATR-X syndrome, in whom a novel missense (C>T) mutation was identified in exon 31 of the ATRX gene.

Cryptic mosaicism involving a second chromosome X in patients with Turner syndrome

The high abortion rate of 45,X embryos indicates that patients with Turner syndrome and 45,X karyotype could be mosaics, in at least one phase of embryo development or cellular lineage, due to the need for the other sex chromosome presence for conceptus to be compatible with life. In cases of structural chromosomal aberrations or hidden mosaicism, conventional cytogenetic techniques can be ineffective and molecular investigation is indicated. Two hundred and fifty patients with Turner syndrome stigmata were studied and 36 who had female genitalia and had been cytogenetically diagnosed as having "pure" 45,X karyotype were selected after 100 metaphases were analyzed in order to exclude mosaicism and the presence of genomic Y-specific sequences (SRY, TSPY, and DAZ) was excluded by PCR. Genomic DNA was extracted from peripheral blood and screened by the human androgen receptor (HUMARA) assay. The HUMARA gene has a polymorphic CAG repeat and, in the presence of a second chromosome with a different HUMARA allele, a second band will be amplified by PCR. Additionally, the CAG repeats contain two methylation-sensitive HpaII enzyme restriction sites, which can be used to verify skewed inactivation. Twenty-five percent (9/36) of the cases showed a cryptic mosaicism involving a second X and approximately 14 percent (5/36), or 55 percent (5/9) of the patients with cryptic mosaicism, also presented skewed inactivation. The laboratory identification of the second X chromosome and its inactivation pattern are important for the clinical management (hormone replacement therapy, and inclusion in an oocyte donation program) and prognostic counseling of patients with Turner syndrome.

Expression of the CTCF gene in bovine oocytes and preimplantation embryos

The CCCTC - binding factor (CTCF) is a protein involved in repression, activation, hormone-inducible gene silencing, functional reading of imprinted genes and X-chromosome inactivation. We analyzed CTCF gene expression in bovine peripheral blood, oocytes and in different cellular stages (2-4 cells, 8-16 cells, 16-32 cells, morulae, and blastocysts) of in vitro fertilized embryos. This is the first report of CTCF expression in oocytes and preimplantation bovine embryos and has implications for the production of embryonic stem cells and the development of novel medical technologies for humans.

The Study of X Chromosome Inactivation Mechanism in Klinefelter's Syndrome by cDNA Microarray Experiment

To investigate the XIST gene expression and its effect in a Klinefelter''s patient, we used Klinefelter''s syndrome (XXY) patient with azoospermia and also used a normal male (XY) and a normal female (XX) as the control, We were performed cytogenetic analysis, Y chromosomal microdeletion assay (Yq), semi-quantitative RT-PCR, and the Northern blot for Klinefelter''s syndrome (KS) patient, a female and a male control, We extracted total RNA from the KS patient, and from the normal cells of the female and male control subjects using the RNA prep kit (Qiagen), cDNA microarray contained 218 human X chromosome-specific genes was fabricated. Each total RNA was reverse transcribed to the first strand cDNA and was labeled with Cy-3 and Cy-5 fluorescein, The microarray was scanned by ScanArray 4000XL system. XIST transcripts were detected from the Klinefelters patient and the female by RT-PCR and Northern blot analysis, but not from the normal male, In the cDNA microarray experiment, we found 24 genes and 14 genes are highly expressed in KS more than the normal male and females, respectively. We concluded that highly expressed genes in KS may be a resulted of the abnormal X inactivation mechanism.

Analysis of X Chromosome Inactivation in Women with Premature Ovarian Failure / 대한산부인과학회잡지

OBJECTIVE: Premature ovarian failure (POF) is a highly heterogenous condition, and its etiology remains unknown in approximately two-thirds of cases. POF can be caused by Turner syndrome, genetic disease, iatrogenic agents such as chemotherapy and radiotherapy, infection and autoimmune disease. X chromosome inactivation is the random process in females during early embryogenesis to achieve dosage compensation with males. But skewed X chromosome inactivation occurs in the female carriers, secondary to cell-autonomous selection against cells in which the abnormal X chromosome is active. Highly skewed X chromosome inactivation is likely to occur in POF which caused by subcytogenetic X chromosome deletion or translocation and X-linked gene mutation. The present study was performed to investigate whether highly skewed inactivation of X chromosome is observed in POF. METHODS: Eighty-six women with premature ovarian failure were studied and eighty-three normal women were enrolled as a control group. X chromosome inactivation pattern were determined by studying methylation pattern of androgen receptor gene. RESULTS: Seventy-six of the 86 POF patients were informative for X chromosome inactivation assay, 8 (10.5%) of them showed highly skewed X chromosome inactivation. In the age matched control group, 3 (4.1%) out of the 74 subjects showed highly skewed X chromosome inactivation. However, this finding is not statistically significant (p=0.2274). Among highly skewed X inactivation, one case of premature ovarian failure revealed 46,XX,del(X)(p21) by high resolution band karyotyping. Therefore highly skewed X inactivation can provide clues to evaluate the causes in POF. CONCLUSION: This study suggests that screening of skewed X chromosome inactivation for the POF will be useful to detect subcytogenetic X chromosome deletion or translocation and X-linked gene mutation associated with POF.

Inactivation of mammalian X-chromosome during spermatogenesis: Temporal expression of genes in the laboratory mouse.

At zygotene/pachytene stage of meiosis in mammalian testis, the X—Y heterobivalent is sequesterd into a heterochromatinized body whose genetic inactivity is shown by lack of uridine incorporation. For the genic level evaluation of the X-inactivation, activities of three X-linked genes were assayed in testicular cell types in the laboratory mouse. While hypoxanthine phosphoribosyl transferase is functional at least up to pachytene stage of primary spermatocytes, glucose-6-phosphate dehydrogenase appears to be active only in the Sertoli cells. No transcript of the muscle specific muscular dystrophin gene was obtained from its regular 5' promoter. Thus, inactivation of X-linked genes in testis occurs at different stages during spermatogenesis, independently of heterochrornatinizati on of the XY-body. We propose that Xist transcript, the putative regulator of X-inactivation in female soma, is also the regulator in testis. However, due to its extremely low level in testis the transcript may regulate by "spreading" in a gradient and affect the genes in a temporal order. Thus, besides other factors, physical proximity of the genes to Xist may determine the stage of their inactivation.

Correlation between X-Inactivation of Different Tissues and Phenotypes in Female with X-Linked Alport Syndrome / 实用儿科临床杂志

Objective To explore the correlation between phenotypes in female with X-linked Alport syndrome(XLAS) and X-inactivation of different tissues.Methods Thirty-six female diagnosed as XLAS were studied,and proteinuria was taken as a marker of the severity of clinical phenotypes.X-inactivation patterns were analyzed in peripheral blood cells of 36 XLAS female and in skin fibroblasts of 12 XLAS female.The X-inactivation analysis was performed by using Hpa Ⅱ predigestion of DNA followed by polymerase chain reaction(PCR) of the highly polymorphic CAG repeat of the androgen receptor gene.Results The average X-inactivation levels of the mutant allele decreased while the degree of proteinuria increased,so there was a negative correlation between the degree of proteinuria and the X-inactivation ratios of the mutant allele in blood cells(r=-0.543,P=0.002).However,there was no correlation between the degree of proteinuria and the X-inactivation ratios of the mutant allele in skin fibroblasts(r=-0.131,P=0.701).Conclusions X-inactivation ratios might explain partially the diverse phenotypes in XLAS female patients,which suggested that the prognosis of XLAS female might be predicted via analysis of the X-inactivation in peripheral blood cells.