Disrupted SOX10 function causes spongiform neurodegeneration in gray tremor mice.

Mice homozygous for the gray tremor (gt) mutation have a pleiotropic phenotype that includes pigmentation defects, megacolon, whole body tremors, sporadic seizures, hypo- and dys-myelination of the central nervous system (CNS) and peripheral nervous system, vacuolation of the CNS, and early death. Vacuolation similar to that caused by prions was originally reported to be transmissible, but subsequent studies showed the inherited disease was not infectious. The gt mutation mapped to distal mouse chromosome 15, to the same region as Sox10, which encodes a transcription factor with essential roles in neural crest survival and differentiation. As dominant mutations in mouse or human SOX10 cause white spotting and intestinal aganglionosis, we screened the Sox10 coding region for mutations in gt/gt DNA. An adenosine to guanine transversion was identified in exon 2 that changes a highly conserved glutamic acid residue in the SOX10 DNA binding domain to glycine. This mutant allele was not seen in wildtype mice, including the related GT/Le strain, and failed to complement a Sox10 null allele. Gene expression analysis revealed significant down-regulation of genes involved in myelin lipid biosynthesis pathways in gt/gt brains. Knockout mice for some of these genes develop CNS vacuolation and/or myelination defects, suggesting that their down-regulation may contribute to these phenotypes in gt mutants and could underlie the neurological phenotypes associated with peripheral demyelinating neuropathy-central dysmyelinating leukodystrophy-Waardenburg syndrome-Hirschsprung disease, caused by mutations in human SOX10.

Spinocerebellar ataxia types 1, 2, 3 and 6: the clinical spectrum of ataxia and morphometric brainstem and cerebellar findings.

To assess the clinical spectrum of ataxia and cerebellar oculomotor deficits in the most common spinocerebellar ataxias (SCAs), we analysed the baseline data of the EUROSCA natural history study, a multicentric cohort study of 526 patients with either spinocerebellar ataxia type 1, 2, 3 or 6. To quantify ataxia symptoms, we used the Scale for the Assessment and Rating of Ataxia (SARA). The presence of cerebellar oculomotor signs was assessed using the Inventory of Non-Ataxia Symptoms (INAS). In a subgroup of patients, in which magnetic resonance images (MRIs) were available, we correlated MRI morphometric measures with clinical signs on an exploratory basis. The SARA subscores posture and gait (items 1-3), speech (item 4) and the limb kinetic subscore (items 5-8) did not differ between the genotypes. The scores of SARA item 3 (sitting), 5 (finger chase) and 6 (nose-finger test) differed between the subtypes whereas the scores of the remaining items were not different. In SCA1, ataxia symptoms were correlated with brainstem atrophy and in SCA3 with both brainstem and cerebellar atrophy. Cerebellar oculomotor deficits were most frequent in SCA6 followed by SCA3, whereas these abnormalities were less frequent in SCA1 and SCA2. Our data suggest that vestibulocerebellar, spinocerebellar and pontocerebellar circuits in SCA1, SCA2, SCA3 and SCA6 are functionally impaired to almost the same degree, but at different anatomical levels. The seemingly low prevalence of cerebellar oculomotor deficits in SCA1 and SCA2 is most probably related to the defective saccadic system in these disorders.

Characterization of a familial case with primary erythromelalgia from Taiwan.

Familial primary erythromelalgia is a rare autosomal dominant disease characterized by redness and painful episodes of the feet and hands, which is often triggered by heat or exercise. In this report, a Taiwanese family with the characteristic features of erythromelalgia is described. Genetic linkage studies established that the disease locus maps to human chromosome 2. Sequence analysis indicated that the disease segregates with a novel mutation in the alpha subunit of the voltage-gated sodium channel (SCN9A or Na(v)1.7). The change observed is predicted to cause the substitution of a highly conserved isoluecine 136 for a valine within the first segment of the transmembrane domain (D1S1). Using immuno-histochemistry to stain a skin biopsy specimen from the affected region, we demonstrate that there is a significant reduction in the number of small fibers.

Identification of forty-five novel and twenty-three known NF1 mutations in Chinese patients with neurofibromatosis type 1.

Neurofibromatosis type 1 (NF1), characterized by skin neurofibromas and an excess of café-au-lait spots, is due to mutations in the neurofibromin (NF1) gene. Identifying the genetic defect in individuals with the disease represents a significant challenge because the gene is extremely large with a high incidence of sporadic mutations across the entire gene ranging from single nucleotide substitutes to large deletions. In the present study, we have used a combination of techniques (heteroduplex analysis, sequencing, loss of heterozygosity and quantification of gene dosage) to define the genetic defect in 68 individuals from a cohort of 107 NF1 Taiwanese patients of Chinese origin. Fifty-eight were initially identified using heteroduplex analytical techniques and confirmed by sequence analysis. A further five were identified by direct sequence analysis alone. The reminders were shown to carry large deletions in the NF1 gene by demonstrating loss of heterozygosity that was confirmed by gene dosage measurements using quantitative-PCR techniques. Mis-sense, non-sense, frame-shift or splice-site mutations were identified across the entire gene of which the majority (45/68) were novel in nature. The detection rate with the various analytical techniques and the types of mutation detected are consistent with published data involving both individuals and large cohort studies from other ethnic backgrounds.

Overweight modulates APOE and APOA5 alleles on the risk of severe hypertriglyceridemia.

BACKGROUND: This study aimed to investigate whether the body mass index (BMI) in combination with genetic variations in APOE and APOA5_'T' alleles modulates the risk of sHTG. METHODS: There were 255 moderate HTG (TG ≥2.26 and <5.65 mmol/L) and 176 sHTG (TG ≥5.65 mmol/L) and 304 controls (TG <2.26 mmol/L) were recruited. APOE epsilon alleles were genotyped using sequence-specific primers; the APOA5_'T' allele (c.553G>T, rs2075291) was identified using a restriction site polymorphism. Overweight/obesity was defined as BMI ≥25 kg/m(2) and non-overweight as BMI <25 kg/m(2). RESULTS: Multivariate logistic regression analysis showed, in addition to APOA5_'T' allele, a significant interaction between BMI ≥25 kg/m(2) and APOE4 carriers on the risk of sHTG. Subjects with diagnosis of diabetes, current smoking, hypertension, levels of non-high density lipoprotein, and BMI ≥25 kg/m(2) were significant determinants of sHTG. The odds ratio (95% confidence intervals) of overweight/obese APOE4 carriers for sHTG was 13.56 (4.89-37.59) more than those of non-overweight non-APOE4 carriers, while the odds ratio for sHTG in overweight/obese patients with the APOA5_'T' allele was 15.83 (7.77-32.26) higher than those of non-overweight non-APOA5 carriers. CONCLUSIONS: Overweight/obesity may potentiate the genetic variants of the APOE4 and APOA5_'T' alleles on the risk of sHTG.

Recent developments in neurofibromatosis type 1.

PURPOSE OF REVIEW: This review summarizes the recent clinical and genetic developments in neurofibromatosis type 1 (NF1) and provides an insight into the possible underlying pathomechanisms. RECENT FINDINGS: NF1, or von Recklinghausen disease, is one of the most common hereditary neurocutaneous disorders in humans. Clinically, NF1 is characterized by café-au-lait spots, freckling, skin neurofibroma, plexiform neurofibroma, bony defects, Lisch nodules and tumors of the central nervous system. The responsible gene, NF1, encodes a 2818 amino acid protein (neurofibromin). Pathological mutations range from single nucleotide substitutions to large-scale genomic deletions dispersed throughout the gene. In addition to the conventional mutation screening methods, a DNA chip microarray-based technology, combinational sequence-based hybridization, has been introduced to expedite mutation detection. Functional analysis has become more amenable following the development of the following: (1) primary Schwann cell cultures from NF1 patients; (2) mouse models; (3) proteomic technologies; and (4) mRNA silencing by RNA interference. These studies have shown that neurofibromin plays a role in adenylate cyclase and AKT-mTOR mediated pathways. It also appears to affect Ras-GTPase activating protein activity through the phosphorylation of protein kinase C which impacts on cell motility by binding with actin in the cytoskeleton. SUMMARY: Recent advances in the clinical features and molecular genetics of NF1 will be discussed together with insights into the underlying pathomechanisms of NF1.

Hereditary sensory neuropathy is caused by a mutation in the delta subunit of the cytosolic chaperonin-containing t-complex peptide-1 (Cct4 ) gene.

A spontaneous autosomal recessive mutation was identified in the Sprague-Dawley rat strain with an early onset sensory neuropathy. The main clinical features of the mutation (mutilated foot, mf ), detectable shortly after birth, include ataxia, insensitivity to pain and foot ulceration. The pathological features include a severe reduction in the number of sensory ganglia and fibres. This mutant is therefore an excellent model for human hereditary sensory neuropathies. Here, we demonstrate that the mf locus maps to the distal end of rat chromosome 14, a region syntenic to human 2p13-p16 and proximal mouse 11. Sequence analysis of four candidate genes in this interval revealed a 1349G>A mutation in the chaperonin (delta) subunit 4 (Cct4) gene associated with the mf mutant. This change resulted in the substitution of a highly conserved cysteine for tyrosine at amino acid 450. Although we did not identify a mutation in the human CCT4 gene in a set of HSN patients, this result clearly demonstrates the pathological consequences of a defect in Cct4, a subunit of CCT (cytosolic chaperonin-containing t-complex peptide-1), involved in folding tubulin, actin and other cytosolic proteins. This is the first report of a mutation in a molecular chaperonin causing a hereditary neuropathy and raises the possibility that mis-folding proteins may be a cause of this group of neuropathies.