Ataxia-ocular apraxia 2 (AOA2) was recently identified as a new autosomal recessive ataxia. We have now identified causative mutations in 15 families, which allows us to clinically define this entity by onset between 10 and 22 years, cerebellar atrophy, axonal sensorimotor neuropathy, oculomotor apraxia and elevated alpha-fetoprotein (AFP). Ten of the fifteen mutations cause premature termination of a large DEAxQ-box helicase, the human ortholog of yeast Sen1p, involved in RNA maturation and termination.We previously identified a 16-cM interval on chromosome 9q34 associated with an autosomal recessive adolescent-onset cerebellar ataxia segregating in two families 1,2 , one with additional oculomotor apraxia 1 and the second with associated elevated serum AFP, immunoglobulins and creatine kinase levels but no oculomotor apraxia 2,3 . We identified nine additional families with ataxia linked to 9q34 by homozygosity mapping (Supplementary Methods online). As most affected individuals had both oculomotor apraxia and elevated AFP levels we assumed that they were affected by the same disorder, which we named AOA2 (OMIM 606002). We identified distal and proximal recombinations in families with two affected individuals (Fig. 1a), localizing the defective gene underlying AOA2 to a 1.1-Mb interval containing 13 genes ( Fig. 1b) and three groups of overlapping spliced expressed-sequence tags, which we analyzed for nucleotide changes but found no mutations. We also found that the unspliced mRNA AK024331 overlaps with the KIAA0625 cDNA and is part of a larger transcript overlapping with additional exons on the 5′ side. We obtained an open reading frame of 8,031 nucleotides and 24 exons (Fig. 1c), of which exon 8 was 4,177 nucleotides long. We confirmed the prediction and size of the transcript by long-range RT-PCR experiments spanning the putative exon 1 and 3′ untranslated region in human fibroblast and lymphoblastoid cell lines (data not shown) and by hybridization of a human northern blot with a probe spanning putative exons 8-24 (Fig. 1d). We also identified an alternative transcript that is 2.4 kb longer, resulting from a second polyadenylation site (human mRNAs AB014525 and AK022902; Fig. 1d).We sequenced exons 1-18 and flanking intronic sequences in families with ataxia linked to this region and in additional individuals with either AOA or ataxia with elevated AFP levels and found 15 different disease-associated mutations in 15 families ( Table 1). Ten of these mutations, including mutations in the two families in whom we first identified AOA2, cause truncation of the protein, indicating that this is the gene underlying AOA2. We found the nonsense mutation R1363X in three unrelated families originating from Portugal, Cabo Verde (once a Portuguese colony) and Spain, suggestive of an Iberian founder event, although recurrent C→T changes on this CpG dinucleotide cannot be formally excluded. Absence of the five missense mutations in 150 unrelated and unaffected individuals sharing the same ethnic origin as the affected in...

The newly recognized ataxia-ocular apraxia 1 (AOA1; MIM 208920) is the most frequent cause of autosomal recessive ataxia in Japan and is second only to Friedreich ataxia in Portugal. It shares several neurological features with ataxia-telangiectasia, including early onset ataxia, oculomotor apraxia and cerebellar atrophy, but does not share its extraneurological features (immune deficiency, chromosomal instability and hypersensitivity to X-rays). AOA1 is also characterized by axonal motor neuropathy and the later decrease of serum albumin levels and elevation of total cholesterol. We have identified the gene causing AOA1 and the major Portuguese and Japanese mutations. This gene encodes a new, ubiquitously expressed protein that we named aprataxin. This protein is composed of three domains that share distant homology with the amino-terminal domain of polynucleotide kinase 3'- phosphatase (PNKP), with histidine-triad (HIT) proteins and with DNA-binding C2H2 zinc-finger proteins, respectively. PNKP is involved in DNA single-strand break repair (SSBR) following exposure to ionizing radiation and reactive oxygen species. Fragile-HIT proteins (FHIT) cleave diadenosine tetraphosphate, which is potentially produced during activation of the SSBR complex. The results suggest that aprataxin is a nuclear protein with a role in DNA repair reminiscent of the function of the protein defective in ataxia-telangiectasia, but that would cause a phenotype restricted to neurological signs when mutant.

Migraine with aura is a common, debilitating, recurrent headache disorder associated with transient and reversible focal neurological symptoms. A role has been suggested for the two-pore domain (K2P) potassium channel, TWIK-related spinal cord potassium channel (TRESK, encoded by KCNK18), in pain pathways and general anaesthesia. We therefore examined whether TRESK is involved in migraine by screening the KCNK18 gene in subjects diagnosed with migraine. Here we report a frameshift mutation, F139WfsX24, which segregates perfectly with typical migraine with aura in a large pedigree. We also identified prominent TRESK expression in migraine-salient areas such as the trigeminal ganglion. Functional characterization of this mutation demonstrates that it causes a complete loss of TRESK function and that the mutant subunit suppresses wild-type channel function through a dominant-negative effect, thus explaining the dominant penetrance of this allele. These results therefore support a role for TRESK in the pathogenesis of typical migraine with aura and further support the role of this channel as a potential therapeutic target.

Objective: Age at onset of diagnostic motor manifestations in Huntington disease (HD) is strongly correlated with an expanded CAG trinucleotide repeat. The length of the normal CAG repeat allele has been reported also to influence age at onset, in interaction with the expanded allele. Due to profound implications for disease mechanism and modification, we tested whether the normal allele, interaction between the expanded and normal alleles, or presence of a second expanded allele affects age at onset of HD motor signs. Methods:We modeled natural log-transformed age at onset as a function of CAG repeat lengths of expanded and normal alleles and their interaction by linear regression. Results:An apparently significant effect of interaction on age at motor onset among 4,068 subjects was dependent on a single outlier data point. A rigorous statistical analysis with a wellbehaved dataset that conformed to the fundamental assumptions of linear regression (e.g., constant variance and normally distributed error) revealed significance only for the expanded CAG repeat, with no effect of the normal CAG repeat. Ten subjects with 2 expanded alleles showed an age at motor onset consistent with the length of the larger expanded allele. Conclusions:Normal allele CAG length, interaction between expanded and normal alleles, and presence of a second expanded allele do not influence age at onset of motor manifestations, indicating that the rate of HD pathogenesis leading to motor diagnosis is determined by a completely dominant action of the longest expanded allele and as yet unidentified genetic or environmental factors. Neurology ® 2012;78:690-695

Ataxia with oculomotor apraxia type 2 (AOA2) is an autosomal recessive disease due to mutations in the senataxin gene, causing progressive cerebellar ataxia with peripheral neuropathy, cerebellar atrophy, occasional oculomotor apraxia and elevated alpha-feto-protein (AFP) serum level. We compiled a series of 67 previously reported and 58 novel ataxic patients who underwent senataxin gene sequencing because of suspected AOA2. An AOA2 diagnosis was established for 90 patients, originating from 15 countries worldwide, and 25 new senataxin gene mutations were found. In patients with AOA2, median AFP serum level was 31.0 microg/l at diagnosis, which was higher than the median AFP level of AOA2 negative patients: 13.8 microg/l, P = 0.0004; itself higher than the normal level (3.4 microg/l, range from 0.5 to 17.2 microg/l) because elevated AFP was one of the possible selection criteria. Polyneuropathy was found in 97.5% of AOA2 patients, cerebellar atrophy in 96%, occasional oculomotor apraxia in 51%, pyramidal signs in 20.5%, head tremor in 14%, dystonia in 13.5%, strabismus in 12.3% and chorea in 9.5%. No patient was lacking both peripheral neuropathy and cerebellar atrophy. The age at onset and presence of occasional oculomotor apraxia were negatively correlated to the progression rate of the disease (P = 0.03 and P = 0.009, respectively), whereas strabismus was positively correlated to the progression rate (P = 0.03). An increased AFP level as well as cerebellar atrophy seem to be stable in the course of the disease and to occur mostly at or before the onset of the disease. One of the two patients with a normal AFP level at diagnosis had high AFP levels 4 years later, while the other had borderline levels. The probability of missing AOA2 diagnosis, in case of sequencing senataxin gene only in non-Friedreich ataxia non-ataxia-telangiectasia ataxic patients with AFP level > or =7 microg/l, is 0.23% and the probability for a non-Friedreich ataxia non-ataxia-telangiectasia ataxic patient to be affected with AOA2 with AFP levels > or =7 microg/l is 46%. Therefore, selection of patients with an AFP level above 7 microg/l for senataxin gene sequencing is a good strategy for AOA2 diagnosis. Pyramidal signs and dystonia were more frequent and disease was less severe with missense mutations in the helicase domain of senataxin gene than with missense mutations out of helicase domain and deletion and nonsense mutations (P = 0.001, P = 0.008 and P = 0.01, respectively). The lack of pyramidal signs in most patients may be explained by masking due to severe motor neuropathy.

Advances in human genetics in recent years have largely been driven by next-generation sequencing (NGS); however, the discovery of disease-related gene mutations has been biased toward the exome because the large and very repetitive regions that characterize the noncoding genome remain difficult to reach by that technology. For autosomal-dominant spinocerebellar ataxias (SCAs), 28 genes have been identified, but only five SCAs originate from non-coding mutations. Over half of SCA-affected families, however, remain without a genetic diagnosis. We used genome-wide linkage analysis, NGS, and repeat analysis to identify an (ATTTC) n insertion in a polymorphic ATTTT repeat in DAB1 in chromosomal region 1p32.2 as the cause of autosomal-dominant SCA; this region has been previously linked to SCA37. The non-pathogenic and pathogenic alleles have the configurations [(ATTTT) 7-400 ] and [(ATTTT) 60-79 (ATTTC) 31-75 (ATTTT) ], respectively. (ATTTC) n insertions are present on a distinct haplotype and show an inverse correlation between size and age of onset. In the DAB1-oriented strand, (ATTTC) n is located in 5 0 UTR introns of cerebellar-specific transcripts arising mostly during human fetal brain development from the usage of alternative promoters, but it is maintained in the adult cerebellum. Overexpression of the transfected (ATTTC) 58 insertion, but not (ATTTT) n , leads to abnormal nuclear RNA accumulation. Zebrafish embryos injected with RNA of the (AUUUC) 58 insertion, but not (AUUUU) n , showed lethal developmental malformations. Together, these results establish an unstable repeat insertion in DAB1 as a cause of cerebellar degeneration; on the basis of the genetic and phenotypic evidence, we propose this mutation as the molecular basis for SCA37.

Familial amyloidotic polyneuropathy (FAP-type I) was first described in Portugal by Andrade in 1952, a time when 54 among 64 patients (belonging to 25 families) originated from Póvoa do Varzim or its surrounding districts. Since then, a total of 1,233 patients, belonging to 489 pedigrees (so far unrelated), have been diagnosed at Centro de Estudos de Paramiloidose, Porto, Portugal. Although age-of-onset showed a wide range (17 to 78 years), 87% of these 1,233 patients developed symptoms before 40 years of age (mean 33.5, SD 9.4 years). Among all patients, 432 belong to 140 families originating from the area of Póvoa do Varzim/Vila do Conde, 330 of whom lived in that area at the time of diagnosis; age-of-onset was, on average, lower than in the overall group of patients (mean 31.1, SD 6.7 years), and no patient had onset after 57 years (versus 3.3% in the global sample). As in previous studies, women were found to have a later onset (33.7) than men (29.0) years. In 1991, the crude prevalence rate was 90.3 x 10(-5) (one in every 1,108 inhabitants), and the frequency of gene carriers was estimated to be 186 x 10(-5) (one in every 538); about 48.4% of these carriers had manifested symptoms by 1991. Female patients had a significantly higher number of children (mean 3.7, SD 2.6) than male patients (mean 2.7, SD 2.1) and the length of their reproductive period (mean 8.4, SD 5.8 yr) was also greater than for men (mean 5.6, SD 4.4 yr). Altogether, the 122 patients who ever reproduced contributed 457 children to the next generation, a mean fertility of 3.7. Further studies using a control groups may answer the question of whether this is the result of a specific high fertility of these patients or just their belonging to a population in natural expansion.

Hereditary autosomal-recessive cerebellar ataxias are a genetically and clinically heterogeneous group of disorders. We used homozygosity mapping and exome sequencing to study a cohort of nine Portuguese families who were identified during a nationwide, population-based, systematic survey as displaying a consistent phenotype of recessive ataxia with oculomotor apraxia (AOA). The integration of data from these analyses led to the identification of the same homozygous PNKP (polynucleotide kinase 3'-phosphatase) mutation, c.1123G>T (p.Gly375Trp), in three of the studied families. When analyzing this particular gene in the exome sequencing data from the remaining cohort, we identified homozygous or compound-heterozygous mutations in five other families. PNKP is a dual-function enzyme with a key role in different pathways of DNA-damage repair. Mutations in this gene have previously been associated with an autosomal-recessive syndrome characterized by microcephaly; early-onset, intractable seizures; and developmental delay (MCSZ). The finding of PNKP mutations associated with recessive AOA extends the phenotype associated with this gene and identifies a fourth locus that causes AOA. These data confirm that MCSZ and some forms of ataxia share etiological features, most likely reflecting the role of PNKP in DNA-repair mechanisms.