Isabel Alonso

A survey of spinocerebellar ataxia in South Brazil : 66 new cases with Machado-Joseph disease, SCA7, SCA8, or unidentified disease-causing mutations

Background The autosomal dominant spinocerebellar ataxias (SCAs) are a clinical and genetically heterogeneous group of debilitating, neurodegenerative diseases, related to fourteen different loci– SCAs 1, 2, 4, 5, 6, 7, 8, 10, 11, 12, 13 and 14, Machado-Joseph disease (MJD/SCA 3), and DRPLA. Objectives (1) to verify the frequency of SCA1, SCA2, MJD, DRPLA, SCA6, SCA7 and SCA8 in a series of new SCA patients from South Brazil and (2) to compare their molecular and clinical characteristics with other patients previously described. Methods sixty-six cases were included in the present study: 52 were familial and 14 sporadic. Molecular analysis of the trinucleotide repeat loci were performed according to methods in the literature. Results 92 % of families with autosomal dominant inheritance segregated the MJD1 mutation, 2 % of families segregated the SCA7 mutation and 6 % remained undiagnosed. Among 14 isolated cases, one showed the SCA8 mutation. Clinical and molecular findings were similar to those already described in the literature, but revealed (1) one SCA7 patient with eyelid retraction, a sign usually related to MJD; and (2) one sporadic case of SCA8. Conclusions The proportion of MJD cases was very high, probably reflecting an Azorean founder effect. The estimated frequency of affected individuals with MJD, in our region, was 1.8 / 100,000, and of SCAs other than MJD, 0.2/100,000.

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.

Mutations in PNKP Cause Recessive Ataxia with Oculomotor Apraxia Type 4

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.

Hereditary ataxia and spastic paraplegia in Portugal: a population-based prevalence study.

IMPORTANCE Epidemiological data on hereditary cerebellar ataxia (HCA) and hereditary spastic paraplegia (HSP) are scarce. OBJECTIVE To present the prevalence and distribution of HCA and HSP in Portugal. DESIGN AND SETTING Population-based, nationwide, systematic survey, from January 1, 1994, through April 15, 2004, in Portugal. PARTICIPANTS Multiple sources of information were used (review of clinical files, active collaboration of neurologists and geneticists, and investigation of affected families), but the main source was active collaboration of general practitioners. Patients were examined by the same team of neurologists, using homogeneous inclusion criteria. The clinical data were registered, and all families were genetically tested. RESULTS Overall, 1336 patients from a population of 10,322 million were diagnosed as having HCA or HSP, a prevalence of 12.9 per 100,000 population. Hereditary cerebellar ataxia was more prevalent (prevalence, 8.9 per 100,000 population; 5.6 for dominant and 3.3 for recessive ataxias) than HSP (prevalence, 4.1 per 100,000 population; 2.4 for dominant and 1.6 for recessive). Machado-Joseph disease (spinocerebellar ataxia type 3) (prevalence, 3.1 per 100,000 population), Friedreich ataxia (prevalence, 1.0 per 100,000 population), and ataxia with oculomotor apraxia (prevalence, 0.4 per 100,000 population) were the most frequent HCAs. Spastic paraplegia types 4 (prevalence, 0.91 per 100,000 population), 3 (prevalence, 0.14 per 100,000 population), and 11 (prevalence, 0.26 per 100,000 population) were the most prevalent HSPs. CONCLUSIONS AND RELEVANCE This population-based survey covered all the Portuguese territory and mobilized most general practitioners and health centers. To our best knowledge, this survey was the largest ever performed for HCA and HSP. Prevalence of autosomal dominant ataxias was high, particularly for Machado-Joseph disease (spinocerebellar ataxia type 3). The genetic cause has not been identified in 39.7% of the patients studied.

Large normal and reduced penetrance alleles in Huntington disease: instability in families and frequency at the laboratory, at the clinic and in the population

Sequeiros J, Ramos EM, Cerqueira J, Costa MC, Sousa A, Pinto‐Basto J, Alonso I. Large normal and reduced penetrance alleles in Huntington disease: instability in families and frequency at the laboratory, at the clinic and in the population.

A novel R1347Q mutation in the predicted voltage sensor segment of the P/Q-type calcium-channel α1A-subunit in a family with progressive cerebellar ataxia and hemiplegic migraine

To the Editor: The CACNA1A gene encodes the highly conserved brain-specific P/Q-type voltage-gated calcium-channel a1A-subunit, expressed mainly in the cerebellum. This channel mediates the entry of calcium ions into cells. This gene is involved in spinocerebellar ataxia type 6 (SCA6), episodic ataxia type 2 (EA2) and familial hemiplegic migraine type 1 (FHM1), which have been considered as distinct clinical entities (1, 2). Recent studies have shown extensive clinical and genetic overlaps between these diseases (3–6). Here, we report a novel missense mutation, located in a region considered to be the voltage sensor of the P/Q-type calcium channel, responsible for both progressive cerebellar ataxia and hemiplegic migraine in all patients from one affected family. We ascertained a Portuguese family with both progressive cerebellar ataxia and hemiplegic migraine, during a population-based survey on hereditary ataxias (7). This family had three patients, two of whom were clinically examined, in two consecutive generations. The proband was a 32-year-old woman presenting with slowly progressive ataxia since her childhood. She experienced a 24-h coma, at the age of 18, after a car accident without head trauma. Magnetic resonance imaging study in this patient showed atrophy of the cerebellum. Nine years later, she had the first episode of hemiplegic migraine that occurred again at a later time. Her brother had the first symptoms at 11 years of age with hemiparesis and aphasia, triggered by physical effort. Hemiparesis and aphasia have recovered after 1week, whereas the signs of gait ataxia have persisted and slowly progressed. No headache was present. Their mother, already deceased, has never been clinically evaluated. We were told by her family members that she had attacks of hemiparesis and aphasia precipitated by physical effort, mainly during the summer season, since she was 11 years of age. By the age of 13, she began to exhibit signs of a slowly progressive ataxia. Mutation analysis of the CACNA1A gene in this family revealed a mobility variant at exon 25 in the two affected sibs but not in their healthy relatives. By direct sequencing, a G-to-A substitution at position 4315 was identified, which produces an arginine-to-glutamine change, at codon 1347, in the CACNA1A gene; this was not present in 100 control chromosomes from the Portuguese general population. This Arg1347 is evolutionarily conserved among a1A-subunits from other species such as Rattus norvegicus, Mus musculus, Drosophila melanogaster and Caenorhabditis elegans, as well as in other a1-subunits. Other mobility variants were detected in this family, indicative of several polymorphisms (Table 1). In the present study, we report a new mutation in the P/Q-type calcium-channel a1A-subunit gene, in a Portuguese family with both slowly progressive cerebellar ataxia and hemiplegic migraine. This mutation replaces a polar positively charged highly conserved arginine by a neutral glutamine, at codon 1347. The two previously described mutations R192Q (1) and R583Q (6, 8) are located in the S4-transmembrane segments of protein domains I and II, respectively (Fig. 1), which are considered to be the voltage sensor segments, both replacing highly conserved positively charged arginines by neutral glutamines. The missense mutation in this family is similar and is also located in the S4-transmembrane segment but of protein domain III. Functional studies performed in channels with the two previously Clin Genet 2004: 65: 70–72 Copyright # Blackwell Munksgaard 2004 Printed inDenmark. All rights reserved CLINICALGENETICS

BDNF and CGRP interaction: implications in migraine susceptibility.

Objectives: Migraine pathophysiology involves several pathways. Our aims were to explore a possible role of the brain-derived neurotrophic factor gene (BDNF) in migraine susceptibility; to study, for the first time, the calcitonin gene-related peptide gene (CGRP); and a possible interaction between the two. Methods: Using a case-control approach, four tagging single nucleotide polymorphisms (SNPs) (rs7124442, rs6265, rs11030107, and rs2049046) of BDNF and one tagging SNP—rs1553005—of CGRP were analyzed in 188 cases and 287 controls. A multivariable logistic regression was performed, adjusting for gender. Allelic and haplotypic frequencies were estimated. Interaction was assessed by a stepwise multivariable-logistic regression and confirmed by a multifactor dimensionality reduction analysis. Results: No significant main effects were found; however, a significant interaction was found between BDNF and CGRP, showing an increased risk for the AT-genotype of rs2049046 and the GC-genotype of rs1553005 (odds ratio = 1.88, 95% confidence interval: 1.20–2.93) for migraineurs. Conclusion: Our data support the hypothesis of an interaction between BDNF and CGRP in migraine susceptibility that should be further explored.

A novel H101Q mutation causes PKCγ loss in spinocerebellar ataxia type 14

AbstractSpinocerebellar ataxia type 14 (SCA14) is an autosomal dominant neurodegenerative disorder, first described in a Japanese family, showing linkage to chromosome 19q13.4-qter. Recently, mutations have been identified in the PRKCG gene in families with SCA14. The PRKCG gene encodes the protein kinase Cγ (PKCγ), a member of a serine/threonine kinase family involved in signal transduction important for several cellular processes, including cell proliferation and synaptic transmission. To identify the disease-causing mutation in a large group of ataxia patients, we searched for mutations in the PRKCG gene. We ascertained 366 unrelated patients with spinocerebellar ataxia, either pure or with associated features such as epilepsy, mental retardation, seizures, paraplegia, and tremor. A C-to-G transversion in exon 4, resulting in a histidine-to-glutamine change at codon 101 of the PKCγ protein, was identified in patients from a family with slowly progressive pure cerebellar ataxia. Functional studies performed in HEK293 cells transfected with normal or mutant construct showed that this mutation affects PKCγ stability or solubility, verified by time-dependent decreased protein levels in cell culture. In conclusion, the H101Q mutation causes slowly progressive uncomplicated ataxia by interfering with PKCγ stability or solubility, which consequently may cause in either case a decrease in the overall PKCγ-dependent phosphorylation.

Ancestral origin of the ATTCT repeat expansion in spinocerebellar ataxia type 10 (SCA10)

Spinocerebellar ataxia type 10 (SCA10) is an autosomal dominant neurodegenerative disease characterized by cerebellar ataxia and seizures. The disease is caused by a large ATTCT repeat expansion in the ATXN10 gene. The first families reported with SCA10 were of Mexican origin, but the disease was soon after described in Brazilian families of mixed Portuguese and Amerindian ancestry. The origin of the SCA10 expansion and a possible founder effect that would account for its geographical distribution have been the source of speculation over the last years. To unravel the mutational origin and spread of the SCA10 expansion, we performed an extensive haplotype study, using closely linked STR markers and intragenic SNPs, in families from Brazil and Mexico. Our results showed (1) a shared disease haplotype for all Brazilian and one of the Mexican families, and (2) closely-related haplotypes for the additional SCA10 Mexican families; (3) little or null genetic distance in small normal alleles of different repeat sizes, from the same SNP lineage, indicating that they are being originated by a single step mechanism; and (4) a shared haplotype for pure and interrupted expanded alleles, pointing to a gene conversion model for its generation. In conclusion, we show evidence for an ancestral common origin for SCA10 in Latin America, which might have arisen in an ancestral Amerindian population and later have been spread into the mixed populations of Mexico and Brazil.

Reduced penetrance of intermediate size alleles in spinocerebellar ataxia type 10

Triplet repeat expansions are the disease-causing mutations in nine dominantly inherited spinocerebellar ataxias (SCAs).1 In 2000, a new type of dynamic mutation was reported in Mexican patients with SCA and seizures, consisting of a (ATTCT)n expansion found in intron 9 of the SCA10 gene2; normal alleles have 10 to 29 and pathologic 800 to 4,500 repeats. We studied 329 unrelated SCA patients. Ataxia was sometimes associated with other features, such as epilepsy, mental retardation, seizures, paraplegia, or tremor; 290 were Portuguese, 39 were from Brazil. Peripheral blood was collected from patients and their relatives, after written informed consent. The (ATTCT)n was amplified by PCR with flanking primers and Southern blot was performed as described elsewhere.2,3 The modified PCR analysis for (ATTCT)n expansion showed that three patients (figure, A and B), from two unrelated Brazilian families, with an admixture of Portuguese and Amerindian ancestry, had a continuous ladder exceeding the product range observed for normal alleles at the SCA10 locus. These patients had first shown a single band after PCR for normal allele sizing (figure, C). Expansion size assessment (figure, D) identified one allele with 400 repeats in Patient II-2 …