In mammals, X-linked gene products can be dosage compensated between males and females by inactivation of one of the two X chromosomes in the developing female embryos. X inactivation choice is usually random in embryo mammals, but several mechanisms can influence the choice determining skewed X inactivation. As a consequence, females heterozygous for X-linked recessive disease can manifest the full phenotype. Herein, we report a family with extremely skewed X inactivation that produced the full phenotype of Lowe syndrome, a recessive X-linked disease, in a female. The X chromosome inactivation studies detected an extremely skewed inactivation pattern with a ratio of 100:0 in the propositus as well as in five out of seven unaffected female relatives in four generations. The OCRL1 ''de novo'' mutation resides in the active paternally inherited X chromosome. X chromosome haplotype analysis suggests the presence of a locus for the familial skewed X inactivation in chromosome Xq25 most likely controlling X chromosome choice in X inactivation or cell proliferation. The description of this case adds Lowe syndrome to the list of X-linked disorders which may manifest the full phenotype in females because of the skewed X inactivation.
Dent's disease is an X-linked renal tubulopathy caused by mutations mainly affecting the CLCN5 gene. Defects in the OCRL1 gene, which is usually mutated in patients with Lowe syndrome, have recently been shown to lead to a Dent-like phenotype, called Dent's disease 2. About 25% of Dent's disease patients do not carry CLCN5/OCRL1 mutations. The CLCN4 and SLC9A6 genes have been investigated, but no mutations have been identified. The recent discovery of a novel mediator of renal amino acid transport, collectrin (the TMEM27 gene), may provide new insight on the pathogenesis of Dent's disease. We studied 31 patients showing a phenotype resembling Dent's disease but lacking any CLCN5 mutations by direct sequencing of the OCRL1 and TMEM27 genes. Five novel mutations, L88X, P161HfsX167, F270S, D506N and E720D, in the OCRL1 gene, which have not previously been reported in patients with Dent's or Lowe disease, were identified among 11 patients with the classical Dent's disease phenotype. No TMEM27 gene mutations were discovered among 26 patients, 20 of whom had an incomplete Dent's disease phenotype. Our findings confirm that OCRL1 is involved in the functional defects characteristic of Dent's disease and suggest that patients carrying missense mutations in exons where many Lowe mutations are mapped may represent a phenotypic variant of Lowe syndrome.
Genetic testing of myotonic dystrophy type 1 (DM1) is very important because it enables the diagnosis and indicates the severity of the disease. Mutation analysis is based on the detection of the number of CTG triplets in the 3' untranslated region of the myotonic dystrophy protein kinase (DMPK) gene. Sometimes it could be complicated by the presence of different patterns of repeat interruptions in the 5' and 3' ends of the expanded alleles recently described in about 3% to 5% of patients. To make molecular diagnosis easier and faster, the use of triplet-primed PCR (TP-PCR) for the detection of expansions in DM1 and other dynamic mutation diseases was proposed. Here we present the results of a retrospective study performed by TP-PCR on 100 subjects previously analyzed by Southern blotting-long PCR.
Dent's disease is an X-linked renal tubulopathy caused by mutations mainly affecting the CLCN5 gene. Defects in the OCRL gene, which is usually mutated in patients with Lowe syndrome, have been shown to lead to a Dent-like phenotype called Dent disease 2. However, about 20% of patients with Dent's disease carry no CLCN5/OCRL mutations. The disease's genetic heterogeneity is accompanied by interfamilial and intrafamilial phenotypic heterogeneity. We report on a case of Dent's disease with a very unusual phenotype (dysmorphic features, ocular abnormalities, growth delay, rickets, mild mental retardation) in which a digenic inheritance was discovered. Two different, novel disease-causing mutations were detected, both inherited from the patient's healthy mother, that is a truncating mutation in the CLCN5 gene (A249fs*20) and a donor splice-site alteration in the OCRL gene (c.388 þ 3A4G). The mRNA analysis of the patient's leukocytes revealed an aberrantly spliced OCRL mRNA caused by in-frame exon 6 skipping, leading to a shorter protein, but keeping intact the central inositol 5-phosphatase domain and the C-terminal side of the ASH-RhoGAP domain. Only wild-type mRNA was observed in the mother's leukocytes due to a completely skewed X inactivation. Our results are the first to reveal the effect of an epistatic second modifier in Dent's disease too, which can modulate its expressivity. We surmise that the severe Dent disease 2 phenotype of our patient might be due to an addictive interaction of the mutations at two different genes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.