Christine Zühlke

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.

Early onset and slow progression of SCA28, a rare dominant ataxia in a large four-generation family with a novel AFG3L2 mutation

Autosomal dominantly inherited spinocerebellar ataxias (SCAs) are a heterogeneous group of neurodegenerative disorders primarily affecting the cerebellum. Genetically, 26 different loci have been identified so far, although the corresponding gene has not yet been determined for 10 of them. Recently, mutations in the ATPase family gene 3-like 2 gene were presented to cause SCA type 28. To define the frequency of SCA28 mutations, we performed molecular genetic analyses in 140 unrelated familial cases with ataxia. Among other variations, we found a novel missense mutation at an evolutionarily conserved amino-acid position using a single-strand conformation polymorphism approach, followed by DNA sequencing. This amino-acid exchange p.E700K was detected in a four-generation German family and was not observed in a survey of 400 chromosomes from healthy control individuals.

Down syndrome and male fertility: PCR-derived fingerprinting, serological and andrological investigations

Down syndrome, the most common birth defect causing mental retardation, is characterized by a specific phenotype including subfertility or sterility and hypogonadism in males. In contrast, several females with Down syndrome have borne offspring. Here, a male with trisomy 21 fathering an infant is described. This observation is verified by serological markers, DNA fingerprinting using different DNA micro‐or minisatellites and andrological investigations.

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.

Aprataxin mutations are a rare cause of early onset ataxia in Germany

Abstract.Aprataxin (APTX) mutations are the cause of ataxia with ocular motor apraxia type 1(AOA1), an autosomal recessive disorder linked to chromosome 9p13.AOA1 seems to be one of the most frequent causes of recessive ataxia in Japan and Portugal. We screened a group of 165 early onset ataxia patients for APTX mutations and detected two non-related patients homozygous for the W293X nonsense mutation. Additionally, we describe several new transcript variants of the APTX gene and discuss their relevance for a sufficient mutation screening.

Autosomal dominant SCA5 and autosomal recessive infantile SCA are allelic conditions resulting from SPTBN2 mutations

Although many genes have been identified for the autosomal recessive cerebellar ataxias (ARCAs), several patients are unlinked to the respective loci, suggesting further genetic heterogeneity. We combined homozygosity mapping and exome sequencing in a consanguineous Egyptian family with congenital ARCA, mental retardation and pyramidal signs. A homozygous 5-bp deletion in SPTBN2, the gene whose in-frame mutations cause autosomal dominant spinocerebellar ataxia type 5, was shown to segregate with ataxia in the family. Our findings are compatible with the concept of truncating SPTBN2 mutations acting recessively, which is supported by disease expression in homozygous, but not heterozygous, knockout mice, ataxia in Beagle dogs with a homozygous frameshift mutation and, very recently, a homozygous SPTBN2 nonsense mutation underlying infantile ataxia and psychomotor delay in a human family. As there was no evidence for mutations in 23 additional consanguineous families, SPTBN2-related ARCA is probably rare.

Recessive dystonia-ataxia syndrome in a Turkish family caused by a COX20 (FAM36A) mutation.

DYTCA is a syndrome that is characterized by predominant dystonia and mild cerebellar ataxia. We examined two affected siblings with healthy, consanguineous, Turkish parents. Both patients presented with a combination of childhood-onset cerebellar ataxia, dystonia, and sensory axonal neuropathy. In the brother, dystonic features were most pronounced in the legs, while his sister developed torticollis. Routine diagnostic investigations excluded known genetic causes. Biochemical analyses revealed a mitochondrial respiratory chain complex IV and a coenzyme Q10 deficiency in a muscle biopsy. By exome sequencing, we identified a homozygous missense mutation (c.154A >C; p.Thr52Pro) in both patients in exon 2 of the COX20 (FAM36A) gene, which encodes a complex IV assembly factor. This variant was confirmed by Sanger sequencing, was heterozygous in both parents, and was absent from 427 healthy controls. The exact same mutation was recently reported in a patient with ataxia and muscle hypotonia. Among 128 early-onset dystonia and/or ataxia patients, we did not detect any other patient with a COX20 mutation. cDNA sequencing and semi-quantitative analysis were performed in fibroblasts from one of our homozygous mutation carriers and six controls. In addition to the exchange of an amino acid, the mutation led to a shift in splicing. In conclusion, we extend the phenotypic spectrum of a recently identified mutation in COX20 to a recessively inherited, early-onset dystonia-ataxia syndrome that is characterized by reduced complex IV activity. Further, we confirm a pathogenic role of this mutation in cerebellar ataxia, but this mutation seems to be a rather rare cause.

Exon deletions and intragenic insertions are not rare in ataxia with oculomotor apraxia 2

BackgroundThe autosomal recessively inherited ataxia with oculomotor apraxia 2 (AOA2) is a neurodegenerative disorder characterized by juvenile or adolescent age of onset, gait ataxia, cerebellar atrophy, axonal sensorimotor neuropathy, oculomotor apraxia, and elevated serum AFP levels. AOA2 is caused by mutations within the senataxin gene (SETX). The majority of known mutations are nonsense, missense, and splice site mutations, as well as small deletions and insertions.MethodsTo detect mutations in patients showing a clinical phenotype consistent with AOA2, the coding region including splice sites of the SETX gene was sequenced and dosage analyses for all exons were performed on genomic DNA. The sequence of cDNA fragments of alternative transcripts isolated after RT-PCR was determined.ResultsSequence analyses of the SETX gene in four patients revealed a heterozygous nonsense mutation or a 4 bp deletion in three cases. In another patient, PCR amplification of exon 11 to 15 dropped out. Dosage analyses and breakpoint localisation yielded a 1.3 kb LINE1 insertion in exon 12 (patient P1) and a 6.1 kb deletion between intron 11 and intron 14 (patient P2) in addition to the heterozygous nonsense mutation R1606X. Patient P3 was compound heterozygous for a 4 bp deletion in exon 10 and a 20.7 kb deletion between intron 10 and 15. This deletion was present in a homozygous state in patient P4.ConclusionOur findings indicate that gross mutations seem to be a frequent cause of AOA2 and reveal the importance of additional copy number analysis for routine diagnostics.

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.