A Novel LMNA Mutation Causes Altered Nuclear Morphology and Symptoms of Familial Partial Lipodystrophy (Dunnigan Variety) with Progeroid Features.

Dunnigan-type partial lipodystrophy (familial partial lipodystrophy, Dunnigan variety, FPLD2) can be caused by LMNA mutations. We identified a novel heterozygous LMNA mutation, P485R, in a patient referred to the International Registry of Werner Syndrome because of features consistent with that of progeroid disorder but who was wild type at the WRN locus. The novel mutation is located 2 amino acids away from the canonical FPLD mutations in exon 8 of the LMNA gene. Immunocytochemical analysis revealed abnormal nuclear morphology characteristic of laminopathies within primary fibroblast cultures, but not in a lymphoblastoid cell line, in keeping with previous observations. Our findings indicate that FPLD2 should be considered in the differential diagnosis of the Werner syndrome.

Gain-of-function mutation in Nav1.7 in familial erythromelalgia induces bursting of sensory neurons.

Erythromelalgia is an autosomal dominant disorder characterized by burning pain in response to warm stimuli or moderate exercise. We describe a novel mutation in a family with erythromelalgia in SCN9A, the gene that encodes the Na(v)1.7 sodium channel. Na(v)1.7 produces threshold currents and is selectively expressed within sensory neurons including nociceptors. We demonstrate that this mutation, which produces a hyperpolarizing shift in activation and a depolarizing shift in steady-state inactivation, lowers thresholds for single action potentials and high frequency firing in dorsal root ganglion neurons. Erythromelalgia is the first inherited pain disorder in which it is possible to link a mutation with an abnormality in ion channel function and with altered firing of pain signalling neurons.

GABA and the ornithine delta-aminotransferase gene in vigabatrin-associated visual field defects.

Vigabatrin use in some epilepsy patients has been associated with persistent visual field constriction and retinal dysfunction. The mechanism is unknown, but could be related to vigabatrin, chronic epilepsy, GABA toxicity, or the effect of a metabolite in combination with a predisposing genotype. The aim of this study was to investigate the latter two hypotheses. Levels of brain gamma-aminobutyric acid (GABA) measured by nuclear magnetic resonance spectroscopy were similar in subjects taking vigabatrin who developed visual field constriction and those who did not. We tested whether allelic heterogeneity of the ornithine aminotransferase gene occurs in the affected patients. No clinically significant mutation was detected, although a common intronic polymorphism was identified.

Clinical and molecular studies in a family with probable X-linked dominant Charcot-Marie-Tooth disease involving the central nervous system.

OBJECTIVE: To investigate the clinical and molecular characteristics of an apparently X-linked dominant form of Charcot-Marie-Tooth (CMT) disease in a family with central nervous system involvement and additional features. BACKGROUND: Charcot-Marie-Tooth disease may be inherited as an autosomal dominant, autosomal recessive, or X-linked trait. In the X-linked dominant form of CMT, females demonstrate milder clinical and electrophysiological features compared with their male relatives. METHODS: Clinical and related examinations were performed in 4 affected individuals from a family with a novel form of CMT affecting males more severely than females. DNA analysis of the connexin 32 (Cx32) gene and proteolipid protein (PLP) gene was performed. We genotyped 3 members of the family to determine which regions of the X chromosome were inherited discordantly in the affected and unaffected brothers. RESULTS: Clinical studies revealed significant spasticity, hyperreflexia, and delayed central conduction, in addition to peripheral neuropathy. Nerve conduction velocities were slower in the affected males than in the affected females. Direct DNA sequencing of the Cx32 coding region and neural-specific promoter were normal. A PLP null mutation was excluded. Levels of very long chain fatty acids were normal. Genotyping studies of the X chromosome supported X-linked inheritance of the neuropathy. CONCLUSIONS: This family differs from others with hereditary motor and sensory neuropathic diseases by the presence of upper motor neuron signs and additional features. The clinical features and inheritance pattern are consistent with X-linked dominant inheritance or autosomal dominant inheritance.

Human GABA(B) receptor 1 gene: eight novel sequence variants.

GABA (gamma-aminobutyric acid) is the principal inhibitory neurotransmitter in the brain. The human GABA(B) receptor (GABBR1) maps to the human leukocyte antigen (HLA) region of chromosome 6. Its function and location in a susceptibility region for schizophrenia, epilepsy, and dyslexia make GABBR1 a candidate gene for neurobehavioral disorders. We report the characterization of GABBR1 gene mutations in 100 chromosomes from a mixed American population. Eleven distinct mutations were found, including two previously reported missense mutations (A20V and G489S) and a previously reported silent 1977 T>C transition. Here, we report four novel silent substitutions (39C>T, 1473T>C, 1476T>C, 1545T>C) and four novel intron variants. These DNA variants may be useful in association and linkage studies of neurobehavioral disorders, and in pharmacogenetic studies of drugs targeting GABBR1.

46,XX gonadal dysgenesis, short stature, and recurrent metabolic acidosis in two sisters.

Gonadal (ovarian) dysgenesis in 46,XX individuals is genetically heterogeneous. We report on two sisters who, in addition to primary ovarian failure, have marked short stature and recurrent episodes of dehydration with metabolic acidosis. Studies performed during one of these episodes suggested mitochondrial dysfunction; however, results of biochemical analysis of electron transport chain activity in skeletal muscle and mitochondrial DNA studies were normal. We discuss the phenotype in relation to previously described conditions of 46,XX gonadal dysgenesis. We suggest this constellation of findings represents a new syndrome.

WRN or telomerase constructs reverse 4-nitroquinoline 1-oxide sensitivity in transformed Werner syndrome fibroblasts.

WRN encodes a RecQ helicase, which is mutated in Werner syndrome. Werner syndrome is a genetic condition of young adults characterized by premature aging, limited replicative capacity of cells in vitro, and increased cancer risk. Telomerase is a reverse transcriptase that extends the G-rich strand of telomeric DNA. Primary cells in vitro typically lack telomerase activity and undergo senescence, whereas telomerase is reactivated in many, but not all, tumors. The roles of the two genes are not known to be related. Here we report the development of an effective colony-forming assay in which a SV40-transformed Werner fibroblast cell line is 6-18-fold more sensitive to 4-nitroquinoline 1-oxide than SV40-transformed normal cell lines. The sensitivity can be partially reversed by transfecting a normal WRN gene but not a mutated WRN gene into the cells. Curiously, the sensitivity can be reversed equally well by transfecting a telomerase gene (TERT) into the cells. These data indicate the possibility of an interdependent function of these two genes.

Renal tubular dysgenesis, absent nipples, and multiple malformations in three brothers: a new, lethal syndrome.

We report on three brothers with renal tubular dysgenesis and absent nipples, each also had other malformations including pre-auricular pits and a preauricular tag, branchial clefts, choanal atresia, pulmonary lobation anomaly, ventricular septal defect, type IIB interrupted aortic arch, absent gallbladder, absent thymus, parathyroid gland, accessory spleen, imperforate anus, clinodactyly, and broad digits and small nails. All three infants died neonatally. This pattern of clinical malformations appears to be a previously unreported syndrome.

Comparison of methods for identifying transcription units and transcription map of the Werner syndrome gene region.

To isolate a human disease gene by positional cloning, a critical step is the identification of candidate genes from a targeted genomic region. We used cDNA selection, exon trapping, and genomic sequencing to identify 12 transcription units from a 1.4-Mb genomic region containing the Werner syndrome gene (WRN). This included sequencing of 650 kb in the region of the WRN gene, to date, the most DNA sequenced as part of a positional cloning effort. The result of this combined method was significant overlap among the transcription units identified by each method; yet, no one method identified all of the transcription units. We present here a comparison of the effectiveness and efficiency of these methods and present a transcription map of the Werner syndrome gene region.

An expression map from human chromosome 14q24.3.

We have constructed an expression map of chromosome 14q24.3 between markers D14S42 and D14S63. cDNA selection with YACs from 14q24.3 was used to generate expressed sequence tags (ESTs). The localization of ESTs was confirmed on a YAC contig. PCR products of ESTs were used as probes to screen cDNA libraries leading to the isolation of transcripts for known and unknown genes. In total, the expression map contains 7 known genes previously mapped to 14q24.3, 6 cDNA transcripts, and 15 anonymous ESTs. The addition of 21 unique transcribed loci from an approximately 5- to 7-Mb region of chromosome 14q24.3 will facilitate future efforts to identify human disease genes from this region.

A YAC, P1, and cosmid contig and 17 new polymorphic markers for the Werner syndrome region at 8p12-p21.

A yeast artificial chromosome (YAC), P1, and cosmid clone contig was constructed for the Werner syndrome (WRN) region of chromosome 8p12-p21 and used to clone a candidate gene for WRN. This region also possibly contains a familial breast cancer locus. The contig was initiated by isolating YACs for the glutathione reductase (GSR) gene and extended in either direction by walking techniques. Sequence-tagged site (STS) markers were generated from subclones of 2 GSR YACs and used to identify P1 and cosmid clones. Additional STSs were generated from P1 and cosmid clones and from potential expressed sequences identified by cDNA selection and exon amplification methods. The final contig was assembled by typing 17 YACs, 20 P1 clones, and 109 cosmids for 54 STS markers. The WRN region could be spanned by 2 nonchimeric YACs covering approximately 1.4 Mb. A P1/cosmid contig was established covering the core 700-800 kb of the WRN region. Fifteen new short tandem repeat polymorphisms and 2 biallelic polymorphic markers were identified and included as STSs in the contig. Analysis of these markers in Werner syndrome subjects demonstrates that the candidate WRN gene is in a region of linkage disequilibrium.

Positional cloning of the Werner's syndrome gene.

Werner's syndrome (WS) is an inherited disease with clinical symptoms resembling premature aging. Early susceptibility to a number of major age-related diseases is a key feature of this disorder. The gene responsible for WS (known as WRN) was identified by positional cloning. The predicted protein is 1432 amino acids in length and shows significant similarity to DNA helicases. Four mutations in WS patients were identified. Two of the mutations are splice-junction mutations, with the predicted result being the exclusion of exons from the final messenger RNA. One of the these mutations, which results in a frameshift and a predicted truncated protein, was found in the homozygous state in 60 percent of Japanese WS patients examined. The other two mutations are nonsense mutations. The identification of a mutated putative helicase as the gene product of the WS gene suggests that defective DNA metabolism is involved in the complex process of aging in WS patients.