PINK1 mutations and parkinsonism.

BACKGROUND: PINK1 loss-of-function causes recessive, early-onset parkinsonism. In Tunisia there is a high rate of consanguineous marriage but PINK1 carrier frequency and disease prevalence have yet to be assessed. OBJECTIVES: The frequency of PINK1 mutations in familial parkinsonism, community-based patients with idiopathic Parkinson disease (PD) (non-familial PD), and control subjects was determined. Demographic and clinical characteristics of individuals with PINK1 homozygous or heterozygous variants, or without PINK1 mutations, were compared. METHODS: A total of 92 kindreds (with 208 affected and 340 unaffected subjects), 240 nonfamilial PD, and 368 control participants were recruited from the Institut National de Neurologie, Tunis. Clinical examinations included Hoehn &Yahr, UPDRS, and Epworth scales. PINK1 sequencing and dosage analysis was performed in familial index patients, the variants identified screened in all subjects. Parkin and LRRK2 genes were also examined. RESULTS: Four PINK1 homozygous mutations, three novel (Q129X, Q129fsX157, G440E, and one previously reported; Q456X), segregate with parkinsonism in 46 individuals in 14 of 92 families (15%). Six of 240 patients with nonfamilial PD were found with either homozygous Q456X or Q129X (2.5%) substitutions. In patients with familial disease, PINK1 homozygotes were younger at disease onset (36 +/- 12 years) than noncarriers (57 +/- 15 years) and more often had an akinetic-rigid presentation at examination and slow progression. CONCLUSIONS: Segregation of PINK1 mutations with parkinsonism within families, and frequency estimates within population controls, suggested only four PINK1 mutations were pathogenic. Several PINK1 sequence variants are potentially benign and there was no evidence that PINK1 heterozygosity increases susceptibility to idiopathic Parkinson disease.

Distinct phenotypes within autosomal recessive ataxias not linked to already known loci.

Autosomal recessive ataxias represent a large group of neurodegenerative disorders characterized by progressive degeneration of central and peripheral nervous systems and a genetic heterogeneity. To analyse clinical, neurophysiological and nerve biopsy findings in 14 Tunisian unrelated families showing linkage exclusion to the known autosomal recessive ataxia loci, 20 Tunisian families with a total of 73 affected subjects were selected on the presence of a clinical phenotype associating a cerebellar ataxia with retained tendon reflexes on at least the index patient. A genetic linkage study was performed with markers spanning the Friedreich ataxia, Spastic ataxia of the Charlevoix-Saguenay, Autosomal recessive ataxia associated with isolated vitamin E deficiency, Ataxia with oculomotor apraxia, Infantile onset spinocerebellar ataxia, Ataxia with Hearing Loss and Optic Atrophy, AT, ATLD, Spinocerebellar ataxia with axonal neuropathy, Cayman ataxia, Cerebellar ataxia with mental retardation optic atrophy and skin abnormalities, Salla syndrome, Marinesco-Sjögren and the Childhood Spinocerebellar Ataxia loci. Out of the 20 families, 4 showed linkage to the spastic ataxia of the Charlevoix-Saguenay locus, one to the Friedreich ataxia locus and one to the Ataxia with oculomotor apraxia locus. Linkage to all tested loci has been excluded in the 14 remaining families. These families were divided into 3 groups according to tendon reflex status in lower limbs which appear as the most obvious distinguishing clinical sign between patients and families: Group A was characterized by brisk tendon reflexes in lower limbs, group B by a homogeneous feature of tendon reflexes with the absence of ankle reflexes and brisk knee reflexes and group C by variable features of tendon reflexes in lower limbs within the same family. Haplotype analysis and Lod score calculation did not show any evidence of linkage to the 16 known loci of cerebellar ataxias. Aim of this study was to reveal the vast clinical phenotypic variability in patients with autosomal recessive ataxia not linked to known loci. Data obtained indicate that detailed clinical and neurophysiological nerve investigations will be essential in order to pool patients within homogeneous subgroups for gene mapping.