LRRK2 Gly2019Ser penetrance in Arab-Berber patients from Tunisia: a case-control genetic study.

BACKGROUND: Several genes have been implicated in the pathogenesis of Parkinson's disease (PD). The aim of this study was to define the clinical symptoms and age-associated cumulative incidence of the most frequent mutation associated with PD, LRRK2 Gly2019Ser. METHODS: 238 patients with sporadic PD and 371 unrelated control participants from the Arab-Berber population were screened at the Institut National de Neurologie, Tunis. Symptoms of PD were assessed using the Hoehn and Yahr scale, the unified Parkinson's disease rating scale, and the Epworth scale. Genotyping for LRRK2 6055G-->A, which causes the Gly2019Ser mutation, was done in all participants, and the age-specific cumulative incidence of PD was calculated by Kaplan-Meier analysis. FINDINGS: 30% of patients with PD in this case-control sample were carriers of LRRK2 Gly2019Ser. The age of onset of symptoms and the clinical presentation of patients with LRRK2 Gly2019Ser were similar to those of patients with idiopathic PD. Carriers of LRRK2 Gly2019Ser were 22.6 times (95% CI 10.2-50.1) more likely to be affected by PD than non-carriers. Tremor was the predominant symptom in LRRK2 Gly2019Ser carriers (92% [homozygotes] vs 75% [heterozygotes] vs 69% [non-carriers]; Cochran-Armitage trend test p=0.0587). Disease severity, response to treatment, and disease duration were similar among LRRK2 Gly2019Ser homozygotes, heterozygotes, and non-carriers (p=0.85). Disease penetrance in LRRK2 Gly2019Ser carriers ranged from less than 20% in those younger than 50 years to greater than 80% at 70 years. INTERPRETATION: The LRRK2 Gly2019Ser mutation in patients with PD is a useful aid to diagnosis. LRRK2 Gly2019Ser penetrance can vary but in most carriers PD seems an inevitable consequence of ageing. LRRK2 Gly2019Ser considerably increases susceptibility to neuronal degeneration, although the process might be mediated by many triggers. By contrast, idiopathic PD is rare before 50 years and the prevalence only increases to 4% in the oldest members of the population. FUNDING: GlaxoSmithKline; National Institutes of Health; and Mayo Foundation.

Autosomal recessive spastic ataxia of Charlevoix-Saguenay: an overview.

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is a distinct form of hereditary early-onset spastic ataxia related to progressive degeneration of the cerebellum and spinal cord. Following the description of the first patients in 1978, the gene responsible has been mapped and identified. It was also shown that the disease occurred worldwide with more than 70 mutations and diverse phenotypes. Because of the random partition of these mutations in the SACS gene particularly on the largest exon nine, and due to the significant clinical variability between patients described in different countries, it has been difficult to establish a genotype-phenotype correlation for the disease. This paper reviews the broad clinical features and the various molecular aspects of ARSACS, reported over the last 30 years highlighting the difficulty of finding correlations.

A novel SACS gene mutation in a Tunisian family.

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is a distinct form of hereditary early-onset spastic ataxia. In 2000, the causative gene, SACS, encoding the protein sacsin, was identified in Quebec patients. The open reading frame (ORF) of SACS was initially reported to contain 11,487 bp and to be encoded by a single gigantic exon. Recently, eight additional exons upstream of the original ORF were found (ENST00000382298). We report four Tunisian ARSACS patients homozygous for a novel mutation in SACS exon 9 gene, c.12846_12850delAGAG. This mutation is localized upstream from the DnaJ domain leading to the loss of this domain, suggesting that the disease is associated with loss of critical chaperone function of sacsin.

Screening for Lrrk2 G2019S and clinical comparison of Tunisian and North American Caucasian Parkinson's disease families.

Mutations in the leucine-rich repeat kinase-2 gene (LRRK2) are responsible for some forms of familial as well as sporadic Parkinson's disease (PD). The purpose of this study was to examine the frequency of a single pathogenic mutation (6055G > A) in the kinase domain of this gene in United States and Tunisian familial PD and to compare clinical characteristics between patients with and without the mutation. Standardized case report forms were used for clinical and demographic data collection. We investigated the frequency of the most common substitution of LRRK2 (G2019S, 6055G>A) and its impact on epidemiological and phenotypic features. The frequency of mutations in Tunisian families was 42% (38/91) and in U.S. families 2.6% (1/39), with the unique opportunity to compare homozygous (n = 23) and heterozygous (n = 109) Tunisian carriers of G2019S substitutions. Individuals with G2019S substitutions had an older age at onset but few other differences compared with families negative for the substitution. Patients with LRRK2 mutations had typical clinical features of PD. Comparisons between individuals with heterozygous and homozygous LRRK2 mutations suggested that gene dosage was not correlated with phenotypic differences; however, the estimated penetrance was greater in homozygotes across all age groups.