Andreas Dalski

Different types of repeat expansion in the TATA-binding protein gene are associated with a new form of inherited ataxia.

A novel neurological syndrome has recently been described to be associated with an expanded polyglutamine domain. The expansion results from partial duplication within the TATA-binding protein (TBP). By investigation of 604 sporadic and familial cases with various forms of neurological syndromes and 157 unaffected individuals, we found repeat expansions in the TBP in four patients of two families with autosomal dominant inheritance of ataxia, dystonia, and intellectual decline. Two different genotypes for the repetitive sequence could be demonstrated which led to elongated polyglutamine stretches between 50 and 55 residues, whereas normal alleles with 27 to a maximum of 44 glutamine residues were found in this study. The expansion to 50 or more glutamine residues results in a pathological phenotype and confirms the report of a new polyglutamine disease.

Mutation analysis in the fibroblast growth factor 14 gene: frameshift mutation and polymorphisms in patients with inherited ataxias

The spinocerebellar ataxias (SCAs) with autosomal dominant inheritance are a group of neurodegenerative disorders with overlapping as well as highly variable phenotypes. Genetically, at least 25 different loci have been identified. Seven SCAs are caused by CAG trinucleotide repeat expansions, for 13 the chromosomal localization is known solely. Recently, a missense mutation in the fibroblast growth factor 14 gene (FGF14) has been reported in a Dutch family with a new dominantly inherited form of SCA. To evaluate the frequency of mutations in the FGF14 gene, we performed molecular genetic analyses for the five exons in 208 nonrelated familial ataxia cases and 208 control samples. In one patient, we detected a novel single base pair deletion in exon 4 (c.487delA) creating a frameshift mutation. In addition, we found DNA polymorphisms in exon 1a, 4, and 5, an amino-acid exchange at position 124, as well as a single-nucleotide polymorphism in the 3′-untranslated region of exon 5.

Extension of the mutation spectrum in Friedreich's ataxia: detection of an exon deletion and novel missense mutations

Friedreichs ataxia (FRDA), the most common autosomal recessively inherited ataxia, is due to a homozygous GAA triplet repeat expansion in the first intron of the FRDA gene in about 96% of patients. Approximately 4% of FRDA patients are compound heterozygotes with a GAA repeat expansion in one allele and a point mutation in the coding region of the second allele. To reinvestigate the mutation spectrum, we searched for mutations including exon deletions in six patients heterozygous for the GAA repeat expansion and found two unknown missense mutations, p.Asn146Lys and p.Leu186Arg, in trans to the expanded FRDA allele. Interestingly, we detected a heterozygous 2776 bp deletion including exon 5a in one of our patients. This deletion removes 50 of the 210 residues of the frataxin. Furthermore, since no FRDA case with two-point mutations is known, we screened eight patients with FRDA phenotype but GAA alleles within the normal range but did not reveal a mutation within the FRDA gene. In addition, DNA polymorphisms have been found in four out of 100 control individuals in this study.

Spinocerebellar ataxia type 1 (SCA1): Phenotype-genotype correlation studies in intermediate alleles

CAG repeat expansions with loss of CAT interruptions in the coding region of the ataxin-1 gene are associated with spinocerebellar ataxia type 1 (SCA1). For molecular genetic diagnosis it is necessary to define the limits of normal and pathological size ranges. In most studies, normal alleles as measured by PCR range from 6–39 units with interruptions of 1–3 CAT trinucleotides that are thought to be involved in the stability of the trinucleotide stretch during DNA replication. Expanded alleles have been reported to carry 39–81 CAG trinucleotides without stabilising CAT interruptions. To evaluate the limits between normal and disease size ranges we analysed the repeat length and composition of the SCA1 gene in 15 individuals with alleles ranging from 36 and 41 triplets for genotype-phenotype correlation studies. We found the 39 trinucleotide-allele to be either interrupted by CAT repeats or formed by a pure CAG stretch. The clinical features of individuals carrying 39 uninterrupted CAG repeats did not differ from the SCA1 phenotype in general with dysphagia, pale discs, pyramidal signs and cerebellar tremor being more frequent as compared to other SCA genotypes. In contrast, the interrupted 39 trinucleotide-allele is not correlated with the SCA1 phenotype.

Spinocerebellar ataxia type 17: report of a family with reduced penetrance of an unstable Gln49 TBP allele, haplotype analysis supporting a founder effect for unstable alleles and comparative analysis of SCA17 genotypes.

BackgroundSpinocerebellar ataxia type 17 (SCA17), a neurodegenerative disorder in man, is caused by an expanded polymorphic polyglutamine-encoding trinucleotide repeat in the gene for TATA-box binding protein (TBP), a main transcription factor. Observed pathogenic expansions ranged from 43 – 63 glutamine (Gln) codons (Gln43–63). Reduced penetrance is known for Gln43–48 alleles. In the vast majority of families with SCA17 an expanded CAG repeat interrupted by a CAA CAG CAA element is inherited stably.ResultsHere, we report the first pedigree with a Gln49 allele that is a) not interrupted, b) unstable upon transmission, and c) associated with reduced penetrance or very late age of onset. The 76-year-old father of two SCA17 patients carries the Gln49 TBP allele but presents without obvious neurological symptoms. His children with Gln53 and Gln52 developed ataxia at the age of 41 and 50. Haplotype analysis of this and a second family both with uninterrupted expanded and unstable pathological SCA17 alleles revealed a common core genotype not present in the interrupted expansion of an unrelated SCA17 patient. Review of the literature did not present instability in SCA17 families with expanded alleles interrupted by the CAA CAG CAA element.ConclusionThe presence of a Gln49 SCA17 allele in an asymptomatic 76-year-old male reams the discussion of reduced penetrance and genotypes producing very late disease onset. In SCA17, uninterrupted expanded alleles of TBP are associated with repeat instability and a common founder haplotype. This suggests for uninterrupted expanded alleles a mutation mechanism and some clinical genetic features distinct from those alleles interrupted by a CAA CAG CAA element.

Mutation of the highly conserved cysteine residue 131 of the SCA14 associated PRKCG gene in a family with slow progressive cerebellar ataxia

Sirs: In contrast to the repeat expansion mutations causing the autosomal dominantly inherited spinocerebellar ataxias SCA1, 2, 3, 6, 7, 8, 10, 12 and 17, a growing number of missense mutations, deletions and splice site variations in the protein kinase Cc gene (PRKCG; OMIM 176980) have been described for patients with SCA14 (OMIM 605361). Protein kinase Cc that is expressed abundantly in the human brain and particularly in Purkinje cells, is thought possibly to be highly involved in signal transduction, synaptic transmission, cell differentiation and proliferation. To date, 17 mutations have been identified in the PRKCG gene (1–8; table 1). Interestingly, eleven of these alterations are located in exon 4 that encodes the evolutionary highly conserved Cys2 subdomain of protein kinase Cc. To evaluate SCA14 frequency, we screened DNA samples of 208 non-related patients with hereditary cerebellar ataxia and of 208 healthy controls for mutations in the regulatory domains C1 and C2 of the PRKCG gene by exon specific PCR, HPLC and sequencing. Expansions at the loci for SCA1, 2, 3, 6, 7, 8, 12, and 17 were excluded. A novel missense mutation was detected in exon 4 in a male patient with autosomal dominant cerebellar ataxia (ADCA). At the amino acid level, the substitution c.T391C results in the exchange of a highly conserved cysteine 131 residue to arginine. The index patient experienced first problems during school sports, especially on the balance beam. His class mates used to tease him for his ‘funny gait’. During adolescence he had to be admitted to the hospital several times for unexplained ‘black-outs’. Repeated EEG recordings did not yield specific epileptic discharges. Subsequently, he was treated for behavioral problems and psychogenic nonepileptic seizures. Around the age of 20 years he developed head tremor, and a moderately slurred speech. MRI confirmed cerebellar atrophy. Nevertheless, he was not diagnosed as ADCA before the age of 40 because a conversion neurotic disease resulting from a wrong primary psychical development caused by a schizoid hysteric personal structure was diagnosed. The examination five years later revealed ataxia of stance, gait and limbs, dysarthria, mild dysphagia and urinary incontinence. Aged 48, he is still ambulatory.

Isolated NIBPL missense mutations that cause Cornelia de Lange syndrome alter MAU2 interaction

Cornelia de Lange syndrome (CdLS; or Brachmann-de Lange syndrome) is a dominantly inherited congenital malformation disorder with features that include characteristic facies, cognitive delays, growth retardation and limb anomalies. Mutations in nearly 60% of CdLS patients have been identified in NIPBL, which encodes a regulator of the sister chromatid cohesion complex. NIPBL, also known as delangin, is a homolog of yeast and amphibian Scc2 and C. elegans PQN-85. Although the exact mechanism of NIPBL function in sister chromatid cohesion is unclear, in vivo yeast and C. elegans experiments and in vitro vertebrate cell experiments have demonstrated that NIPBL/Scc2 functionally interacts with the MAU2/Scc4 protein to initiate loading of cohesin onto chromatin. To test the significance of this model in the clinical setting of CdLS, we fine-mapped the NIBPL–MAU2 interaction domain and tested the functional significance of missense mutations and variants in NIPBL and MAU2 identified in these minimal domains in a cohort of patients with CdLS. We demonstrate that specific novel mutations at the N-terminus of the MAU2-interacting domain of NIBPL result in markedly reduced MAU2 binding, although we appreciate no consistent clinical difference in the small group of patients with these mutations. These data suggest that factors in addition to MAU2 are essential in determining the clinical features and severity of CdLS.

Ciliary neurotrophic factor influences endocrine adipocyte function: inhibition of leptin via PI 3-kinase

Ciliary neurotrophic factor (CNTF), originally known for its involvement in the modulation of neuronal growth, has been discovered to exert anorexigenic effects and is currently being investigated in clinical studies for the treatment of obesity and insulin resistance. This neuropeptide acts on the central nervous system. However, we have recently demonstrated direct peripheral effects on adipocyte signalling and thermogenesis. Given the emerging endocrine role of adipose tissue in the regulation of energy homeostasis and insulin resistance, we investigated potential effects of CNTF on leptin expression and secretion. Our study demonstrates a direct inhibition of leptin expression and secretion by acute and chronic CNTF treatment. Furthermore, we demonstrate a differentiation- and Janus kinase 2 (JAK2)-independent, but phosphatidylinositol 3-kinase-dependent signalling pathway mediating this negative effect. These results provide novel evidence for a role of CNTF in the selective modulation of adipocyte endocrine function which may have important implications for the regulation of energy homeostasis.

Quantitative PCR analysis of different splice forms of NFAT5 revealed specific gene expression in fetal and adult brain.

To investigate sequences or mutations associated with neurodegenerative disorders, we performed analyses for the NFAT5 gene, which is located in the candidate region for the autosomal dominantly inherited spinocerebellar ataxia type 4 (SCA4). PCR based expression analyses detected NFAT5 transcripts with alternative splicing in 27 fetal and adult human tissues. Interestingly, by using quantitative methods on cDNA from fetal and adult human brain a significant difference at the expression level for one splice form could be shown.

Screening of the SPTBN2 (SCA5) gene in German SCA patients

AbstractThe spinocerebellar ataxias (SCAs) with autosomal dominant inheritance are a clinically and genetically heterogeneous group of neurodegenerative disorders. To date 27 different loci have been identified for these conditions. Recently, two deletions as well as one missense mutation in the beta-III spectrin gene (STBN2) were identified causing SCA5. To evaluate the clinical relevance of these mutations, we screened 310 familial and sporadic patients with ataxia. While none of the individuals tested had evidence for one of the known SCA5 mutations, additional sequencing of the coding region for 22 unrelated patients revealed three novel missense exchanges at evolutionary conserved amino acid positions. Even though each variation marks a unique genotype in 250 alleles, a disease causing capacity can be excluded with high probability. These results reflect the challenges for molecular analyses in SCA5.