Gene In Xq28 Research Articles

A Novel Form of Familial Vasopressin Deficient Diabetes Insipidus Transmitted in an X-linked Recessive Manner.

Familial pituitary diabetes insipidus has been described only in an autosomal dominant or recessive mode of inheritance. This work aims to determine the cause of a novel form of familial diabetes insipidus (DI) that is controlled by desmopressin therapy but segregates in an X-linked recessive manner. Thirteen members from 3 generations of the kindred with familial DI were studied. Water intake, urine volume, urine osmolality, plasma osmolality, and plasma vasopressin were measured under basal conditions, during fluid deprivation, 3% saline infusion, and water loading. Magnetic resonance images of the posterior pituitary also were obtained. In affected males, the effects of desmopressin therapy and linkage of the DI to markers for chromosome Xq28 were determined. In addition, the genes encoding vasopressin, aquaporin-2, the AVPR2 receptor, and its flanking regions were sequenced. This study showed that 4 males from 3 generations of the kindred have DI that is due to a deficiency of vasopressin, is corrected by standard doses of desmopressin, and segregates with markers for the AVPR2 gene in Xq28. However, no mutations were found in AVPR2 or its highly conserved flanking regions. Exome sequencing confirmed these findings and also revealed no deleterious variants in the provasopressin and aquaporin-2 genes. The 4 obligate female carriers osmo-regulated vasopressin in the low normal range. X-linked recessive transmission of DI can be due to a defect in either the secretion or the action of vasopressin. Other criteria are necessary to differentiate and manage the 2 disorders correctly.

47 patients with FLNA associated periventricular nodular heterotopia.

BackgroundHeterozygous loss of function mutations within the Filamin A gene in Xq28 are the most frequent cause of bilateral neuronal periventricular nodular heterotopia (PVNH). Most affected females are reported to initially present with difficult to treat seizures at variable age of onset. Psychomotor development and cognition may be normal or mildly to moderately impaired. Distinct associated extracerebral findings have been observed and may help to establish the diagnosis including patent ductus arteriosus Botalli, progressive dystrophic cardiac valve disease and aortic dissection, chronic obstructive lung disease or chronic constipation. Genotype-phenotype correlations could not yet be established.MethodsSanger sequencing and MLPA was performed for a large cohort of 47 patients with Filamin A associated PVNH (age range 1 to 65 years). For 34 patients more detailed clinical information was available from a structured questionnaire and medical charts on family history, development, epileptologic findings, neurological examination, cognition and associated clinical findings. Available detailed cerebral MR imaging was assessed for 20 patients.ResultsThirty-nine different FLNA mutations were observed, they are mainly truncating (37/39) and distributed throughout the entire coding region. No obvious correlation between the number and extend of PVNH and the severity of the individual clinical manifestation was observed. 10 of the mutation carriers so far are without seizures at a median age of 19.7 years. 22 of 24 patients with available educational data were able to attend regular school and obtain professional education according to age.ConclusionsWe report the clinical and mutation spectrum as well as MR imaging for a large cohort of 47 patients with Filamin A associated PVNH including two adult males. Our data are reassuring in regard to psychomotor and cognitive development, which is within normal range for the majority of patients. However, a concerning median diagnostic latency of 17 to 20 years was noted between seizure onset and the genetic diagnosis, intensely delaying appropriate medical surveillance for potentially life threatening cardiovascular complications as well as genetic risk assessment and counseling prior to family planning for this X-linked dominant inherited disorder with high perinatal lethality in hemizygous males.

Mouse Tafazzin Is Required for Male Germ Cell Meiosis and Spermatogenesis.

Barth syndrome is an X-linked mitochondrial disease, symptoms of which include neutropenia and cardiac myopathy. These symptoms are the most significant clinical consequences of a disease, which is increasingly recognised to have a variable presentation. Mutation in the Taz gene in Xq28 is thought to be responsible for the condition, by altering mitochondrial lipid content and mitochondrial function. Male chimeras carrying a targeted mutation of Taz on their X-chromosome were infertile. Testes from the Taz knockout chimeras were smaller than their control counterparts and this was associated with a disruption of the progression of spermatocytes through meiosis to spermiogenesis. Taz knockout ES cells also showed a defect when differentiated to germ cells in vitro. Mutant spermatocytes failed to progress past the pachytene stage of meiosis and had higher levels of DNA double strand damage and increased levels of endogenous retrotransposon activity. Altogether these data revealed a novel role for Taz in helping to maintain genome integrity in meiosis and facilitating germ cell differentiation. We have unravelled a novel function for the Taz protein, which should contribute to an understanding of how a disruption of the Taz gene results in the complex symptoms underlying Barth Syndrome.

Does the human X contain a third evolutionary block? Origin of genes on human Xp11 and Xq28

Comparative gene mapping of human X-borne genes in marsupials defined an ancient conserved region and a recently added region of the eutherian X, and the separate evolutionary origins of these regions was confirmed by their locations on chicken chromosomes 4p and 1q, respectively. However, two groups of genes, from the pericentric region of the short arm of the human X (at Xp11) and a large group of genes from human Xq28, were thought to be part of a third evolutionary block, being located in a single region in fish, but mapping to chicken chromosomes other than 4p and 1q. We tested this hypothesis by comparative mapping of genes in these regions. Our gene mapping results show that human Xp11 genes are located on the marsupial X chromosome and platypus chromosome 6, indicating that the Xp11 region was part of original therian X chromosome. We investigated the evolutionary origin of genes from human Xp11 and Xq28, finding that chicken paralogs of human Xp11 and Xq28 genes had been misidentified as orthologs, and their true orthologs are represented in the chicken EST database, but not in the current chicken genome assembly. This completely undermines the evidence supporting a separate evolutionary origin for this region of the human X chromosome, and we conclude, instead, that it was part of the ancient autosome, which became the conserved region of the therian X chromosome 166 million years ago.

A novel p.Arg970X mutation in the last exon of the CDKL5 gene resulting in late-onset seizure disorder

Classic Rett Syndrome (RS) is a neurodevelopmental disorder due to mutations in the MECP2 gene in Xq28. Atypical RS with severe early-onset encephalopathy and therapy-resistant epilepsy can be due to mutations in the CDKL5 (Cyclin-Dependent Kinase-like 5) gene in Xp22. We here report a 14-year-old female with a RS-like clinical picture, and well-controlled seizures. MECP2 gene testing was negative, but subsequent sequencing of the CDKL5 gene revealed the c. 2908 C > T nonsense mutation (p.Arg970X) in the last exon, not previously described in other patients or controls. The less severe phenotype might be due to the position of the mutation in the last exon of the CDKL5 gene.

Distal Xq duplication and functional Xq disomy

Distal Xq duplications refer to chromosomal disorders resulting from involvement of the long arm of the X chromosome (Xq). Clinical manifestations widely vary depending on the gender of the patient and on the gene content of the duplicated segment. Prevalence of Xq duplications remains unknown. About 40 cases of Xq28 functional disomy due to cytogenetically visible rearrangements, and about 50 cases of cryptic duplications encompassing the MECP2 gene have been reported. The most frequently reported distal duplications involve the Xq28 segment and yield a recognisable phenotype including distinctive facial features (premature closure of the fontanels or ridged metopic suture, broad face with full cheeks, epicanthal folds, large ears, small and open mouth, ear anomalies, pointed nose, abnormal palate and facial hypotonia), major axial hypotonia, severe developmental delay, severe feeding difficulties, abnormal genitalia and proneness to infections. Xq duplications may be caused either by an intrachromosomal duplication or an unbalanced X/Y or X/autosome translocation. In XY males, structural X disomy always results in functional disomy. In females, failure of X chromosome dosage compensation could result from a variety of mechanisms, including an unfavourable pattern of inactivation, a breakpoint separating an X segment from the X-inactivation centre in cis, or a small ring chromosome. The MECP2 gene in Xq28 is the most important dosage-sensitive gene responsible for the abnormal phenotype in duplications of distal Xq. Diagnosis is based on clinical features and is confirmed by CGH array techniques. Differential diagnoses include Prader-Willi syndrome and Alpha thalassaemia-mental retardation, X linked (ATR-X). The recurrence risk is significant if a structural rearrangement is present in one of the parent, the most frequent situation being that of an intrachromosomal duplication inherited from the mother. Prenatal diagnosis is performed by cytogenetic testing including FISH and/or DNA quantification methods. Management is multi-specialist and only symptomatic, with special attention to prevention of malnutrition and recurrent infections. Educational and rehabilitation support should be offered to all patients.Disease nameXq duplications, Xq functional disomy

Atypical X‐chromosome inactivation in an X;1 translocation patient demonstrating Xq28 functional disomy

X-chromosome inactivation (XCI) is an epigenetic process used to regulate gene dosage in mammalian females by silencing genes on one X-chromosome. While the pattern of XCI is typically random in normal females, abnormalities of the X-chromosome may result in skewing due to disadvantaged cell growth. We describe a female patient with an X;1 translocation [46,X,t(X;1)(q28;q21)] and unusual pattern of XCI who demonstrates functional disomy of the Xq28 region distal to the translocation breakpoint. There was complete skewing of XCI in the patient, along with the atypical findings of an active normal X chromosome and an inactive derivative X. Characterization of the translocation revealed that the patient's Xq28 breakpoint interrupts the DKC1 gene. Molecular analysis of the breakpoint region revealed functional disomy of Xq28 genes distal to DKC1. We propose that atypical XCI occurred in the patient due to a post-inactivation cell selection mechanism likely initiated by disruption of DKC1. As a result, the pattern of XCI is opposite that of the expected for an X;autosome translocation. Therefore, we suggest the phenotypic abnormalities found in the patient are a result of functional disomy in the Xq28 region.

The systematic functional characterisation of Xq28 genes prioritises candidate disease genes

BackgroundWell known for its gene density and the large number of mapped diseases, the human sub-chromosomal region Xq28 has long been a focus of genome research. Over 40 of approximately 300 X-linked diseases map to this region, and systematic mapping, transcript identification, and mutation analysis has led to the identification of causative genes for 26 of these diseases, leaving another 17 diseases mapped to Xq28, where the causative gene is still unknown. To expedite disease gene identification, we have initiated the functional characterisation of all known Xq28 genes.ResultsBy using a systematic approach, we describe the Xq28 genes by RNA in situ hybridisation and Northern blotting of the mouse orthologs, as well as subcellular localisation and data mining of the human genes. We have developed a relational web-accessible database with comprehensive query options integrating all experimental data. Using this database, we matched gene expression patterns with affected tissues for 16 of the 17 remaining Xq28 linked diseases, where the causative gene is unknown.ConclusionBy using this systematic approach, we have prioritised genes in linkage regions of Xq28-mapped diseases to an amenable number for mutational screens. Our database can be queried by any researcher performing highly specified searches including diseases not listed in OMIM or diseases that might be linked to Xq28 in the future.

Presence of filamin in the astrocytic inclusions of Aicardi syndrome

Aicardi syndrome affects only females and has been hypothesized to be an X-linked dominant male-lethal disorder. Because no familial cases can be studied for genetic linkage analysis, the mutated gene has remained elusive. With the goal of selecting genes for mutation analysis by a functional candidate approach, a detailed pathologic analysis of two brains from deceased Aicardi syndrome patients was performed. The presence of micrencephaly, absent or hypoplastic corpus callosum, polymicrogyria, heterotopia, ventriculomegaly, intracerebral cyst, and intracytoplasmic eosinophilic inclusions was confirmed in glial fibrillary acidic protein–positive astrocytes in the cortex and heterotopias, but not in white matter. The inclusions demonstrated strong immunolabeling with antibodies to filamin and vimentin but weak labeling with antibodies to proteins S100 and microtubule-associated protein 1. These findings suggested that an underlying defect in the cytoskeleton, which involves filamin, may cause this condition. Because the filamin A gene in Xq28 is mutated in another disorder with heterotopia, familial bilateral periventricular heterotopia, mutation analysis of filamin A in Aicardi syndrome patients was pursued. No mutations were found, and the full-length protein was expressed in both brain samples. Future studies will focus on investigation of X-linked genes that may affect function of filamin or other cytoskeletal proteins.

X-linked hydrocephalus: a novel missense mutation in the L1CAM gene

X-linked hydrocephalus is associated with mutations in the L1 neuronal cell adhesion molecule gene. L1 protein plays a key role in neurite outgrowth, axonal guidance, and pathfinding during the development of the nervous system. A male is described with X-linked hydrocephalus who had multiple small gyri, hypoplasia of the white matter, agenesis of the corpus callosum, and lack of cleavage of the thalami. Scanning the L1 neuronal cell adhesion molecule gene in Xq28 revealed a novel missense mutation: transition of a guanine to cytosine at position 1,243, which led to conversion of alanine to proline at position 415 in the Ig 4 domain of the L1 protein. It is likely that the X-linked hydrocephalus and cerebral dysgenesis are a result of the abnormal structure and function of the mutant L1 protein.

A Mutation Hot Spot for Nonspecific X-Linked Mental Retardation in the MECP2 Gene Causes the PPM-X Syndrome

We report here the genetic cause of the X-linked syndrome of psychosis, pyramidal signs, and macro-orchidism (PPM-X) in a three-generation family manifesting the disorder as a mutation in the methyl-CpG binding-protein 2 (MECP2) gene in Xq28. The A140V mutation was found in all affected males and all carrier females in the family. To date, descriptions have been published of two patients with independent familial mental retardation (MR) and two patients with sporadic MR who harbor this specific mutation in the MECP2 gene. This strongly suggests that A140V is a hot spot of mutation resulting in moderate to severe MR in males. A simple and reliable PCR approach has been developed for detection of the hot spot A140V mutation to prescreen any other unexplained cases of MR before further extensive mutation analyses.

Infantile Dilated X-Linked Cardiomyopathy, G4.5 Mutations, Altered Lipids, and Ultrastructural Malformations of Mitochondria in Heart, Liver, and Skeletal Muscle

Mutations in the Xq28 gene G4.5 lead to dilated cardiomyopathy (DCM). Differential splicing of G4.5 results in a family of proteins called “tafazzins” with homology to acyltransferases. These enzymes assemble fatty acids into membrane lipids. We sequenced G4.5 in two kindreds with X-linked DCM and in two unrelated men, one with idiopathic DCM and the other with DCM of arrhythmogenic right ventricular dysplasia. We examined the ultrastructure of heart, liver, and muscle biopsy specimens in these three DCM types; we used gas chromatography to compare fatty acid composition in heart, liver, and muscle autopsy specimens of two patients of kindred 1 with that of controls. In X-linked DCM, G4.5 had a stop codon (E188X), a nonsense mutation, in kindred 1 and an amino acid substitution (G240R), a missense mutation, in kindred 2. In the two men with isolated DCM, G4.5 was not mutated. Ultrastructural mitochondrial malformations were present in the biopsy tissues of the patients with DCM. Cardiac biopsy specimens of both kindreds with X-linked DCM exhibited greatly enlarged mitochondria with large bundles of stacked, compacted, disarrayed cristae that differed from those of the two types of isolated DCM. Autopsy tissue of patients with X-linked DCM had decreased unsaturated and increased saturated fatty acid concentrations. Seven of 13 published G4.5 missense mutations, including the one presented here, occur in acyltransferase motifs. Impaired acyltransferase function could result in increased fatty acid saturation that would decrease membrane fluidity. Mitochondrial membrane proliferation may be an attempt to compensate for impaired function of acyltransferase. Cardiac ultrastructure separates X-linked DCM with G4.5 mutations from the two types of isolated DCM without G4.5 mutations. Electron microscopy of promptly fixed myocardial biopsy specimens has a role in defining the differential diagnosis of DCM. Mutational analysis of the G4.5 gene also serves this purpose.

Genomic rearrangement in NEMO impairs NF-kappaB activation and is a cause of incontinentia pigmenti. The International Incontinentia Pigmenti (IP) Consortium.

Familial incontinentia pigmenti (IP; MIM 308310) is a genodermatosis that segregates as an X-linked dominant disorder and is usually lethal prenatally in males. In affected females it causes highly variable abnormalities of the skin, hair, nails, teeth, eyes and central nervous system. The prominent skin signs occur in four classic cutaneous stages: perinatal inflammatory vesicles, verrucous patches, a distinctive pattern of hyperpigmentation and dermal scarring. Cells expressing the mutated X chromosome are eliminated selectively around the time of birth, so females with IP exhibit extremely skewed X-inactivation. The reasons for cell death in females and in utero lethality in males are unknown. The locus for IP has been linked genetically to the factor VIII gene in Xq28 (ref. 3). The gene for NEMO (NF-kappaB essential modulator)/IKKgamma (IkappaB kinase-gamma) has been mapped to a position 200 kilobases proximal to the factor VIII locus. NEMO is required for the activation of the transcription factor NF-kappaB and is therefore central to many immune, inflammatory and apoptotic pathways. Here we show that most cases of IP are due to mutations of this locus and that a new genomic rearrangement accounts for 80% of new mutations. As a consequence, NF-kappaB activation is defective in IP cells.

Nephrogenic diabetes insipidus

In nephrogenic diabetes insipidus, the kidney is unable to concentrate urine despite normal or elevated concentrations of the antidiuretic hormone arginine vasopressin (AVP). In congenital nephrogenic diabetes insipidus (NDI), the obvious clinical manifestations of the disease, that is polyuria and polydipsia, are present at birth and need to be immediately recognized to avoid severe episodes of dehydration. Most (>90%) congenital NDI patients have mutations in the AVPR2 gene, the Xq28 gene coding for the vasopressin V 2 (antidiuretic) receptor. In <10% of the families studied, congenital NDI has an autosomal recessive inheritance and mutations of the aquaporin-2 gene ( AQP2), ie, the vasopressin-sensitive water channel, have been identified. When studied in vitro, most AVPR2 mutations lead to receptors that are trapped intracellularly and are unable to reach the plasma membrane. A minority of the mutant receptors reach the cell surface but are unable to bind AVP or to trigger an intracellular cyclic adenosine-monophosphate (cAMP) signal. Similarly AQP2 mutant proteins are trapped intracellularly and cannot be expressed at the luminal membrane. The acquired form of NDI is much more common than the congenital form, is almost always less severe, and is associated with downregulation of AQP2. The advances described here are examples of “bedside physiology” and provide diagnostic tools for physicians caring for these patients.

Functional studies of twelve mutant V2 vasopressin receptors related to nephrogenic diabetes insipidus

X-linked nephrogenic diabetes insipidus (NDI) is a rare disease with defective renal and extrarenal arginine vasopressin V2 receptor responses due to mutations in the AVPR2 gene in Xq28. To study the cause of loss of function of mutant V2 receptors, we expressed 12 mutations (N55H, L59P, L83Q, V88M, 497CC-->GG, deltaR202, I209F, 700delC, 908insT, A294P, P322H, P322S) in COS-7 cells. Eleven of these, including P322H, were characterized by a complete loss of function, but the mutation P322S demonstrated a mild clinical and in vitro phenotype. This was characterized by a late diagnosis without any growth or developmental delay and a significant increase in urine osmolality after intravenous 1-deamino[D-Arg8]AVP administration. In vitro, the P322S mutant was able to partially activate the Gs/adenylyl cyclase system in contrast to the other V2R mutants including P322H, which were completely inactive in this regard. This showed not only that Pro 322 is important for proper V2R coupling, but also that the degree of impairment is strongly dependent on the identity of the substituting amino acid. Three-dimensional modeling of the P322H and P322S mutant receptors suggested that the complete loss of function of the P322H receptor could be due, in part, to hydrogen bond formation between the His 322 side chain and the carboxyl group of Asp 85, which does not occur in the P322S receptor.

MTM1 gene mutations in Japanese patients with the severe infantile form of myotubular myopathy.

The severe infantile form of myotubular myopathy is a fatal muscle disease that predominantly affects male infants and is characterized by severe weakness and hypotonia from birth. X-linked myotubular myopathy was found to be associated with mutations in the MTM1 gene in Xq28 encoding the putative tyrosine phosphatase, myotubularin. We screened the MTM1 gene for mutations in seven Japanese patients (six males and one female) who had the diagnosis of severe infantile form of myotubular myopathy. We found five mutations, including three novel mutations based on sequence analysis of RT-PCR fragments covering the entire open reading frame. Two patients (one male and one female), who had similar clinicopathologic features, did not have any mutation in the MTM1 gene open reading frame, suggesting that they may have had an autosomal recessive disease.

Evaluation of two X chromosomal candidate genes for Rett syndrome: Glutamate dehydrogenase-2 (GLUD2) and rab GDP-dissociation inhibitor (GDI1)

The most likely cause of the Rett syndrome (RTT) is an X-linked dominant mutation lethal in hemizygous males. Previous exclusion mapping studies have identified putative regions for the RTT gene on the X chromosome. In the present study, we evaluated two candidate genes, glutamate dehydrogenase-2 (GLUD2) and rab GDP-dissociation inhibitor (GDI1/XAP-4), chosen because of their expression patterns and functions in the central nervous system and their location in the nonexcluded region of Xq. The intronless gene GLUD2, located in Xq25 and expressed in neuronal and testicular tissues, is involved in the metabolism of glutamate, a neurotransmitter reported to be elevated in the spinal fluid of RTT individuals. The GLUD2 gene was screened for mutations by Southern hybridization and by direct sequencing of polymerase chain reaction (PCR) products. The GDI1 gene in Xq28, also known as RABGDIA or XAP-4, encodes a human GDI that is expressed predominantly in neuronal and sensory tissues. All 11 exons and splice junctions of the GDI1 gene were PCR-amplified and sequenced directly or screened by single-strand conformation analysis. No mutation in either of these two genes was found in 22 RTT patients. Therefore, GLUD2 and GDI1 can be excluded as candidate genes for this syndrome.

Differential Expression of XAP5, a Candidate Disease Gene

We have isolated a full-length cDNA corresponding to the XAP5 gene in Xq28. An unusual feature of the cDNA is that it contains runs of CCG repeats in the 5′ untranslated region, typical of genes that exhibit anticipation. It has a striking pattern of differential expression and is greatly enhanced in various fetal tissues. This predicted protein encodes a unique 339-amino-acid polypeptide that contains a large percentage of highly charged residues and a possible nuclear localization signal. A comparison to genomic sequence shows that XAP-5 comprises 13 exons spanning 6.5 kb. An examination of the human population indicates that the longest CCG run is polymorphic and varies in length from 8 to 12 repeats.

The X-Linked Gene G4.5 Is Responsible for Different Infantile Dilated Cardiomyopathies

Barth syndrome (BTHS) is an X-linked disorder characterized clinically by the associated features of cardiac and skeletal myopathy, short stature, and neutropenia. The clinical manifestations of the disease are, in general, quite variable, but cardiac failure as a consequence of cardiac dilatation and hypertrophy is a constant finding and is the most common cause of death in the first months of life. X-linked cardiomyopathies with clinical manifestations similar to BTHS have been reported, and it has been proposed that they may be allelic. We have recently identified the gene responsible for BTHS, in one of the Xq28 genes, G4.5. In this paper we report the sequence analysis of 11 additional familial cases: 8 were diagnosed as possibly affected with BTHS, and 3 were affected with X-linked dilated cardiomyopathies. Mutations in the G4.5 gene were found in nine of the patients analyzed. The molecular studies have linked together what were formerly considered different conditions and have shown that the G4.5 gene is responsible for BTHS (OMIM 302060), X-linked endocardial fibroelastosis (OMIM 305300), and severe X-linked cardiomyopathy (OMIM 300069). Our results also suggest that very severe phenotypes may be associated with null mutations in the gene, whereas mutations in alternative portions or missense mutations may give a "less severe" phenotype.

Fried syndrome is a distinct X linked mental retardation syndrome mapping to Xp22.

In 1972, Fried described a large Scottish family affected by X linked mental retardation (XLMR), hydrocephalus, and mild facial dysmorphism. The phenotype has considerable similarity to the MASA syndrome, which...