Expanded Alleles Research Articles

STR typing of ductal adenocarcinomas of the pancreas and healthy control tissue in 18 individuals

Recently, different work groups have demonstrated that short tandem repeat (STR) typing of various tumor tissues may lead to erroneous results due to tumor microsatellite instability (MSI). This may have considerable implications for genetic profiling of tumor tissue, e.g. in paternity testing or sample individualization. To elucidate whether this is true for ductal adenocarcinomas (DAC) of the pancreas, we genetically investigated tumor and corresponding healthy tissue from 18 patients using a commercially available multiplex PCR kit commonly used in forensic laboratories. STR typing of the samples revealed no differences between tumor and healthy tissue in 17 out of 18 samples. One sample, however, showed an allele expansion at locus D21S11. In heterozygous cases, peak heights varied strongly at different loci, mocking a loss of heterozygozity. This investigation shows that even though tetranucleotide MSI in pancreatic DAC is a rare event, the interpretation of genetic profiles obtained from cancerous samples can be difficult and lead to misinterpretations.

Understanding the dynamics of Spinocerebellar Ataxia 8 (SCA8) locus through a comparative genetic approach in humans and apes

Spinocerebellar Ataxia 8 (SCA8) is a neurodegenerative disorder caused by expansion of a trinucleotide repeat. We undertake a comparative genetic analysis among human populations and primate species in the normal variation range, where forces that shaped present diversity can be recognised. We determinate number of repeats of the short tandem repeat through allele length sizing and sequencing methods. Human allele distributions are very similar among populations, ruling out ethnicity as a genetic risk for allele expansion. Primate comparison shows human-specific features, with longer human alleles due to a novel variable trinucleotide repeat, not present in non-human primates, which increased the disease-causing expansion likelihood. SCA8 seems to be a human specific disease.

The GAA triplet-repeat sequence in Friedreich ataxia shows a high level of somatic instability in vivo, with a significant predilection for large contractions.

Friedreich ataxia is commonly caused by large expansions of a GAA triplet-repeat (GAA-TR) sequence in the first intron of the FRDA gene. We used small-pool PCR to analyze somatic variability among 7190 individual FRDA molecules from peripheral blood DNA of subjects carrying 12 different expanded alleles, ranging in size from 241 to 1105 triplets. Expanded alleles showed a length-dependent increase in somatic variability, with mutation loads ranging from 47% to 78%. We noted a strong contraction bias among long alleles (>500 triplets), which showed a 4-fold higher frequency of large contractions versus expansions. Some contractions were very large; of all somatic mutations scored, approximately 5% involved contractions of >50% of the original allele length, and 0.29% involved complete reversion to the normal/premutation length (< or =60 triplets). These observations contrast sharply with the strong expansion bias seen in expanded CTG triplet repeats in myotonic dystrophy. No somatic variability was detected in >6000 individual FRDA molecules analyzed from 15 normal alleles (8-25 triplets). A premutation allele with 44 uninterrupted GAA repeats was found to be unstable, ranging in size from 6 to 113 triplets, thus establishing the threshold for somatic instability between 26 and 44 GAA triplets. Analysis of an additional 7850 FRDA molecules from serially passaged lymphoblastoid cell lines carrying nine expanded alleles (132-933 triplets) showed very low mutation loads, ranging from 0% to 6.2%. Our data indicate that expanded GAA-TR alleles in Friedreich ataxia are highly mutable and have a natural tendency to contract in vivo, and that these properties depend on multiple factors, including DNA sequence, triplet-repeat length and unknown cell-type-specific factors.

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.

Premutation and intermediate-size FMR1 alleles in 10572 males from the general population: loss of an AGG interruption is a late event in the generation of fragile X syndrome alleles.

We previously reported a 1:259 prevalence of female carriers of FMR1 premutation-size alleles (greater than 54 triplet repeats) in the general population. We now have screened 10 572 independent males from the same population for similar alleles using high-throughput Southern blotting. We identified 13 male carriers of an allele with more than 54 repeats. This corresponds to a prevalence of 1:813 males (95% confidence interval 1:527 to 1:1781). Haplotype analysis of four markers flanking the triplet array revealed that the prevalence of the major fragile X mutation-associated haplotype was increased among FMR1 alleles of 40-54 repeats. Although sequencing of highly unstable premutation alleles from fragile X families revealed only pure CGG tracts, this was not the case for alleles of similar size that were identified in males from the general population. Forty-eight out of forty-nine alleles of 40 or more triplets had one or two AGG interruptions. This observation, combined with the observation of the enrichment of major fragile X syndrome haplotypes in all alleles of this size, is evidence that the loss of an AGG interruption in the triplet repeat array is not necessary for expansion of normal alleles of 29-30 triplets to intermediate size. The loss of AGG interruptions thus appears to be a late event that leads to greatly increased instability and may be related to the haplotype background of specific FMR1 alleles.

Comorbid genetic diseases, von Hippel-Lindau disease and spinocerebellar ataxia type 2, confounding the diagnosis of cerebellar dysfunction in an adolescent

The authors report a 15-year-old female who presented with difficulties in ambulation as well as difficulties with balance and penmanship. She had a known genetic risk of von Hippel-Lindau (VHL; MIM 193300) disease, with a unique VHL mutation, but had no tumors of the brain or spine to explain her symptoms. Laboratory analysis of peripheral blood lymphocytes was targeted at genetic loci associated with ataxic disorders. Allelic expansion of the ataxin-2 gene was identified. Spinocerebellar ataxia type 2 (SCA2) was diagnosed as a comorbid genetic condition in this patient.

Preimplantation genetic diagnosis (PGD) of myotonic dystrophy (DM) by triplet primed PCR (TP-PCR): a protocol applicable to all at-risk couples.

Objective: Positive selection of unaffected embryos in the course of DM PGD has so far been based on the detection of the normal allele of the transmitting parent. This indirect diagnosis has mostly been carried out using the morbid CAG locus. From our sample of patients, about 1/4 of the couples were fully informative or non informative and 1/2 were semi informative. For the latter, half of the healthy embryos cannot be diagnosed, leaving for transfer only 25% of the starting embryos. This sort of diagnosis is therefore applicable satisfactorily to only 1/4 of the at risk couples. Our objective was to develop a simple and reliable single cell assay which can be applicable to all DM couples. Design: We wanted to develop a test allowing the detection of the pathological allele in DM. DM alleles can expand up to several thousands triplets, and, at the moment, the largest alleles can not always be PCR amplified even from milligrams of DNA. We therefore decided to amplify only part of the expansion using an oligonucleotide primer internal to the repeat itself as described in Warner et al. (1996). We needed to modify their protocol to achieve reliable amplification from single DNA copies. [∗Warner JP, Barron LH, Goudie D, Kelly K, Dow D, Fitzpatrick DR, Brock DJ. (1996) J Med Genet. 33 (12):1022–6.] Materials/Methods: Single cells were lysed in alkaline buffer (200 mM KOH, 50 mM DTT) and amplified with the expand Long template Taq polymerase and buffer II (Roche diagnosis). Hemi-nested amplification was carried out in a 9700 PCR system with a specific forward primer (O/I F) and the reverse triplet specific reverse primer elongated in 3′ with 20 nucleotides constituting a reverse inner primer. The inner amplification contained the O/I F primer fluorescently labeled with 6 FAM and the tail part only of the triplet primer. Twenty and twenty five thermal cycles were carried out for the outer and the inner reactions respectively. Fluorescent TP-PCR products were analyzed in a ABI 310 DNA analyzer. Each run takes about 30 minutes, so, for semi informative patients we decided to speed up the process by analyzing the PCR products by non fluorescent polyacrylamide gel electrophoresis and only running the non informative allelic combinations in the ABI 310. Results: Expanded alleles were detected in 100% of the lymphocytes analysed and one PGD cycle was carried out for a semi informative couple. Four embryos were biopsied and only two yielded a PCR product from each of their 2 biopsied blastomeres. In all 4 cells, only the shared allele was detectable after traditional gel electrophoresis. After fluorescent analysis there was no trace of TP amplification in any of the cells and both embryos were transferred. Positive hCG were measured in the first dosage but had decreased in the second. Ten blastomeres were desaggregated from the two remaining embryos and all positive cells showed TP-amplified product indicating the presence of the expanded allele in both these embryos. Conclusions: Reliable detection of expanded CAG repeats was achieved from single lymphocytes and blastomeres using fluorescent TP-PCR. One chemical pregnancy was achieved using this diagnosis technique. Supported by: This work was supported in part by the association Française contre les myopaties (AFM) and l’assistance publique des hopitaux de Paris (AP-HP).

Instability at dinucleotide and trinucleotide repeats in breast cancer.

We analyzed 7 mono-, 6 di- and 2 trinucleotide repeat loci in a well characterized series of 69 breast cancer cases, treated in the period 1985-1986 and followed for 12 years. Tumor-associated allele contractions or expansions were observed only at di- and trinucleotide repeats, and were detected in 14/69 cases (20%), of which 7 (10%) showed instability at 2 or more loci (10%). No alterations were detected at mononucleotide repeats known to be unstable in gastrointestinal tumors with the microsatellite mutator phenotype. Disease-free survival at 5 years, overall survival at 12 years of follow-up, tumor stage, estrogen/progesteron receptor status, and expression of the Ki-67 proliferation marker were independent of microsatellite status.

Hereditary Ataxias

Hereditary Ataxias

High Germinal Instability of the (CTG) n at the SCA8 Locus of Both Expanded and Normal Alleles

The autosomal dominant spinocerebellar ataxias (SCAs) are a group of late-onset, neurodegenerative disorders for which 10 loci have been mapped (SCA1, SCA2, SCA4-SCA8, SCA10, MJD, and DRPLA). The mutant proteins have shown an expanded polyglutamine tract in SCA1, SCA2, MJD/SCA3, SCA6, SCA7, and DRPLA; a glycine-to-arginine substitution was found in SCA6 as well. Recently, an untranslated (CTG)n expansion on chromosome 13q was described as being the cause of SCA8. We have now (1) assessed the repeat size in a group of patients with ataxia and a large number of controls, (2) examined the intergenerational transmission of the repeat, and (3) estimated the instability of repeat size in the sperm of one patient and two healthy controls. Normal SCA8 chromosomes showed an apparently trimodal distribution, with classes of small (15-21 CTGs), intermediate (22-37 CTGs), and large (40-91 CTGs) alleles; large alleles accounted for only0.7% of all normal-size alleles. No expanded alleles (>/=100 CTGs) were found in controls. Expansion of the CTG tract was found in five families with ataxia; expanded alleles (all paternally transmitted) were characterized mostly by repeat-size contraction. There was a high germinal instability of both expanded and normal alleles: in one patient, the expanded allele (152 CTGs) had mostly contraction in size (often into the normal range); in the sperm of two normal controls, contractions were also more frequent, but occasional expansions into the upper limit of the normal size range were also seen. In conclusion, our results show (1) no overlapping between control (15-91) and pathogenic (100-152) alleles and (2) a high instability in spermatogenesis (both for expanded and normal alleles), suggesting a high mutational rate at the SCA8 locus.

A novel minisatellite repeat expansion identified at FRA16B in a Japanese carrier.

Previously, the allelic expansion of a 33-bp AT-rich minisatellite repeat has been reported to cause FRA16B, a distamycin A-inducible fragile site. Here, we identified a novel 35-bp minisatellite repeat at FRA16B in a Japanese carrier. The nucleotide sequence of the 35-bp minisatellite was highly AT-rich and nearly identical to the 33-bp one but with insertion of two nucleotides, thymine and adenine. The copy number of the AT-rich minisatellite was 21 in total in the carrier, while only a few copies of the 33-bp minisatellite were present in a non-carrier Japanese subject. These results suggest that the molecular mechanism involved in the allelic expansion of the minisatellite repeat in FRA16B recognizes both minisatellites, the 33-bp one and the 35-bp one, as an amplicon. These observations were different from the ones at folate-sensitive fragile sites, where the CCG triplet repeat was commonly involved in the allelic expansion. Although a slight reduction in AT content (95% > 90%) in the region of minisatellite expansion in the carrier subject was observed, both AT-content and length of the highly AT-rich region seem to play important roles in the cytogenetic expression of the distamycin A-inducible fragile site. In another normal subject, without fragile site expression, allelic expansion involving the 33-bp minisatellite was observed, and the length of the AT-rich DNA region was increased up to approximately 1000 bp. Since the length of the AT-rich minisatellite region was increased up to approximately 1,100-bp in the carrier subject, the threshold length for the cytogenetic expression of the AT-rich DNA region may be between about 1,000-bp and 1,100-bp.

Frequency of spinocerebellar ataxia types 1, 2, 3, 6, and 7 in Australian patients with spinocerebellar ataxia.

The frequencies of various genetically defined spinocerebellar ataxias (SCAs) vary in different populations presumably due to founder effects. No data have been published on the Australian population. Although predominantly of Anglo-Celtic extraction, Australia has also received considerable influx from southeastern Europe and more recently eastern and southeastern Asia. We examined the frequency of mutations for SCA types 1, 2, 3, 6, and 7 in southeastern Australia. Of 88 pedigrees with multiple-affected members, SCA type 1 (SCA1) accounted for 16%, SCA2 for 6%, SCA3 for 12%, SCA6 for 17%, SCA7 for 2%, and 47% (41 pedigrees) were negative for each of SCA1, 2, 3, and 6. Twenty of the 41 negative pedigrees were also negative for dentatorubralpallidoluysian atrophy, and indeed dentatorubralpallidoluysian atrophy has not been reported in Australia. In addition, no pedigree information was available on a further four patients with SCA1, three patients with SCA2, three patients with SCA3, and three patients with SCA6. One SCA1 and two SCA2 patients had no other known affected family members. In total, of 63 pedigrees or individuals with positive tests, 30% were those with SCA1, 15% with SCA2, 22% with SCA3, 30% with SCA6, and 3% with SCA7. Judging by pedigree names, four of the nine SCA2 positive individuals/pedigrees were of Italian extraction, and four of the 14 SCA3 positive individuals/pedigrees were of Chinese descent, whereas only 1 of the 20 SCA1 positive individuals/pedigrees were non-Anglo-Celtic. These results are in accordance with the known ethnic composition of the Australian population and with gene frequencies in these constituent ethnic groups reported by others. The frequency of large-normal alleles for SCA1 and SCA3 in the population reflects the prevalence of these two diseases, supporting the hypothesis that disease alleles arise by expansion of large-normal alleles.

Cis-acting modifiers of expanded CAG/CTG triplet repeat expandability: associations with flanking GC content and proximity to CpG islands.

An increasing number of human genetic disorders are associated with the expansion of trinucleotide repeats. The majority of these diseases are associated with CAG/CTG expansions, including Huntington's disease, myotonic dystrophy and many of the spinocerebellar ataxias. Recently, two new expanded CAG/CTG repeats have been identified that are not associated with a phenotype. Expanded alleles at all of these loci are unstable, with frequent length changes during intergenerational transmission. However, variation in the relative levels of instability, and the size and direction of the length change mutations observed, between the CAG/CTG loci is apparent. We have quantified these differences, taking into account effects of progenitor allele length, by calculating the relative expandability of each repeat. Since the repeat motifs are the same, these differences must be a result of flanking sequence modifiers. We present data that indicate a strong correlation between the relative expandability of these repeats and the flanking GC content. Moreover, we demonstrate that the most expandable loci are all located within CpG islands. These data provide the first insights into the molecular bases of cis -acting flanking sequences modifying the relative mutability of dispersed expanded human triplet repeats.

A Single Polymerase Chain Reaction-Based Protocol for Detecting Normal and Expanded Alleles in Myotonic Dystrophy

The myotonic dystrophy (DM) expansion varies from 50 to 4000 CTG repeats in the 3' untranslated region of the DMPK gene. Direct analysis by Southern blot, after restriction enzyme digestion of genomic DNA, is the method of choice for studying the DM mutation. A long polymerase chain reaction (PCR)-formatted protocol, which involved a single genomic in vitro amplification followed by high concentration agarose gel electrophoresis and oligo-specific hybridization, was used to amplify normal alleles and DM alleles in all examined ranges of expansion (up to 3,700 CTGs) starting from a small amount of genomic DNA (> or = 15 pg). This method is quick, sensitive, and reproducible and reduces the cost of diagnostic laboratory processing.

SCA6 mutation analysis in a large cohort of the Japanese patients with late-onset pure cerebellar ataxia

Spinocerebellar ataxia type 6 (SCA6) is caused by small CAG repeat expansion in the gene encoding the α 1A-voltage-dependent-calcium channel subunit (CACNL1A4) on chromosome 19p13, and is a subgroup of the late-onset pure cerebellar ataxia (ADCA III). To investigate the prevalence of SCA6 in the Japanese, we analyzed this mutation in 23 families and 12 probands with ADCA III. The specificity and stability of the CAG repeat were examined in additional individuals and families with other miscellaneous dominant SCAs. The CAG expansion of SCA6 gene was exclusively observed in 12 of 23 families (52%) and 12 proband cases with ADCA III, but not in others. The CAG repeat was 21–33 in the disease-associated alleles ( n=56), and 4–18 in normal alleles ( n=1148). Expanded alleles were stable during transmission, and a significant inverse correlation for CAG repeat number with age at onset was noted. Our results indicate that SCA6 shares approximately half of the ADCA III in the Japanese, and that gene mutations causing the remaining, have yet to be identified.

A distamycin A-inducible fragile site, FRA8E, located in the region of the hereditary multiple exostoses gene, is not involved in HPV16 DNA integration and amplification

The rare fragile site is a specific point on a chromosome that is expressed as an isochromatid gap or break under certain conditions of cell culture and is inherited in a Mendelian codominant fashion. Five folate-sensitive fragile sites were cloned, and the molecular basis of fragile site mutation was shown to be a new class of mutation, called dynamic mutation, resulting from an allelic expansion of (CCG)n repeats. The mechanism responsible for other types of rare fragile sites, i.e., distamycin A-inducible and BrdU-requiring, is unknown, although cytogenetic studies suggested that these fragile sites play a mechanistic role in breakage and recombination and may also be integration and modification sites of foreign viral DNA genomes. A distamycin A-inducible fragile site, FRA8E, is mapped to 8q24.1 in which various loci implicated in genomic instability are located. Here we identified a YAC clone spanning both FRA8E and the hereditary multiple exostosis (EXT1) gene, using fluorescence in situ hybridization (FISH) analysis of a yeast artificial chromosome (YAC) contig. By using P1 clones as probes, the FRA8E locus was further localized to a 400-kb region including the EXT1 gene. Furthermore, the integration and amplification site of human papillomovirus 16 DNA in the ASCC (argyrophil small cell carcinoma) cells were shown not to coincide with FRA8E, but to be involved in an extensively broad genomic region of 8q24.1, including the c-myc gene.

Molecular analysis and clinical findings in the Spanish Gaucher disease population: putative haplotype of the N370S ancestral chromosome.

Gaucher disease (GD) is an autosomal recessive disorder caused by mutations in the lysosomal beta-glucocerebrosidase (GBA) gene. As the disease is particularly prevalent among Ashkenazi Jews, most studies have been carried out on this ethnic group. In the current study, we present a mutation analysis of the GBA gene in Spanish patients together with the clinical findings. We conducted a systematic analysis in 53 unrelated GD patients. The GBA gene was initially scanned for nine previously described mutations by ASO hybridization or restriction analysis after PCR amplification. The remaining unidentified alleles were screened by nonisotopic PCR-SSCP analysis and sequenced. This approach allowed the identification of 101 of 106 GD alleles (95.3%) involving 24 different mutations, 11 of which are described for the first time: G113E (455G-->A), T134P (517A-->C), G389E (1283G-->A), P391L (1289C-->T), N392I (1292A-->T), Y412H (1351T-->G), W(-4)X (108G-->A), Q169X (662C-->T), R257X (886C-->T), 500insT, and IVS5+1G-->T. Most mutations are present in one or few GD chromosomes. However, two mutations, N370S (1226A-->G) and L444P (1448T-->C), are very frequent and account for 66.1% of the total number of alleles. Linkage disequilibrium was detected between these two mutations and an intragenic polymorphism, indicating that expansion of founder alleles occurred in both cases. Analysis of several microsatellite markers close to the GBA gene allowed us to establish the putative haplotype of the ancestral N370S chromosome.

Molecular analysis and clinical findings in the Spanish Gaucher disease population: Putative haplotype of the N370S ancestral chromosome

Gaucher disease (GD) is an autosomal recessive disorder caused by mutations in the lysosomal β-glucocerebrosidase (GBA) gene. As the disease is particularly prevalent among Ashkenazi Jews, most studies have been carried out on this ethnic group. In the current study, we present a mutation analysis of the GBA gene in Spanish patients together with the clinical findings. We conducted a systematic analysis in 53 unrelated GD patients. The GBA gene was initially scanned for nine previously described mutations by ASO hybridization or restriction analysis after PCR amplification. The remaining unidentified alleles were screened by nonisotopic PCR-SSCP analysis and sequenced. This approach allowed the identification of 101 of 106 GD alleles (95.3%) involving 24 different mutations, 11 of which are described for the first time: G113E (455G→A), T134P (517A→C), G389E (1283G→A), P391L (1289C→T), N392I (1292A→T), Y412H (1351T→G), W(-4)X (108G→A), Q169X (662C→T), R257X (886C→T), 500insT, and IVS5+1G→T. Most mutations are present in one or few GD chromosomes. However, two mutations, N370S (1226A→G) and L444P (1448T→C), are very frequent and account for 66.1% of the total number of alleles. Linkage disequilibrium was detected between these two mutations and an intragenic polymorphism, indicating that expansion of founder alleles occurred in both cases. Analysis of several microsatellite markers close to the GBA gene allowed us to establish the putative haplotype of the ancestral N370S chromosome. Hum Mutat 11:295–305, 1998. © 1998 Wiley-Liss, Inc.

Spinocerebellar ataxia type 6. Molecular and clinical features of 35 Japanese patients including one homozygous for the CAG repeat expansion.

Spinocerebellar ataxia type 6 (SCA6) is a newly classified autosomal-dominant cerebellar ataxia (ADCA) associated with CAG repeat expansion. We screened 111 patients with cerebellar ataxia for the SCA6 mutation. Of these, 35 patients were found to have expanded CAG repeats in the SCA6 gene, indicating that second to SCA3, SCA6 is the most common ADCA in Japan. Expanded alleles ranged from 21 to 29 repeats, whereas normal alleles had seven to 17 repeats. There was no change in the CAG repeat length during meiosis. The age at onset was inversely correlated with the repeat length. The main clinical feature of the 35 patients with SCA6 was slowly progressive cerebellar ataxia; multisystem involvement was not common. The 35 patients included nine cases without apparent family history of cerebellar ataxia. The sporadic cases had smaller CAG repeats (21 or 22 repeats) and a later age at onset (64.9 +/- 4.9 years) than the other cases with established family history. We also identified one patient who was homozygous for the SCA6 repeat expansion. The homozygote showed an earlier age of onset and more severe clinical manifestations than her sister, a heterozygote carrying an expanded allele with the same repeat length as the homozygote. This finding suggests that the dosage of the CAG repeat expansion plays an important role in phenotypic expression in SCA6.

Spinocerebellar ataxia type 2. Genotype and phenotype in German kindreds.

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant cerebellar ataxia (ADCA) for which the disease-causing mutation has recently been characterized as an expanded CAG trinucleotide repeat. We investigated 64 families of German ancestry with ADCA and 55 patients with sporadic ataxia for the SCA2 mutation. Expanded alleles were found in 6 of the 64 families and in 1 patient with sporadic ataxia. This patient had a de novo mutation from an intermediate paternal allele. Length of repeats in 21 patients with SCA2 ranged from 36 to 52 CAG motifs and was inversely correlated with age at onset and progression of the disease. Expanded alleles were unstable during meiosis; paternal transmission especially caused significant anticipation of onset up to 26 years earlier. The SCA2 phenotype differed from those of SCA1 and SCA3 with higher frequencies of slowed ocular movements, postural and action tremor, myoclonus, and hyporeflexia. However, no single feature was sufficient to permit a specific clinical diagnosis. Spinocerebellar ataxia type 2 accounts for about 10% of German families with ADCA but may also be present in sporadic ataxia due to de novo mutations. Clinical features are highly variable among and even within families. However, the size of the expanded repeat influences the phenotype and is relevant for course and prognosis of the disease.