Mutations in the parkin gene occur among individuals with PD with an older age at onset (> or =60 years) who have a positive family history of the disease. In addition, the clinical findings of parkin-positive individuals are remarkably similar to those without mutations.

Parkinson disease (PD) is a common neurodegenerative disorder characterized by bradykinesia, resting tremor, muscular rigidity, and postural instability, as well as by a clinically significant response to treatment with levodopa. Mutations in the alpha-synuclein gene have been found to result in autosomal dominant PD, and mutations in the parkin gene produce autosomal recessive juvenile-onset PD. We have studied 203 sibling pairs with PD who were evaluated by a rigorous neurological assessment based on (a) inclusion criteria consisting of clinical features highly associated with autopsy-confirmed PD and (b) exclusion criteria highly associated with other, non-PD pathological diagnoses. Families with positive LOD scores for a marker in an intron of the parkin gene were prioritized for parkin-gene testing, and mutations in the parkin gene were identified in 22 families. To reduce genetic heterogeneity, these families were not included in subsequent genome-screen analysis. Thus, a total of 160 multiplex families without evidence of a parkin mutation were used in multipoint nonparametric linkage analysis to identify PD-susceptibility genes. Two models of PD affection status were considered: model I included only those individuals with a more stringent diagnosis of verified PD (96 sibling pairs from 90 families), whereas model II included all examined individuals as affected, regardless of their final diagnostic classification (170 sibling pairs from 160 families). Under model I, the highest LOD scores were observed on chromosome X (LOD score 2.1) and on chromosome 2 (LOD score 1.9). Analyses performed with all available sibling pairs (model II) found even greater evidence of linkage to chromosome X (LOD score 2.7) and to chromosome 2 (LOD score 2.5). Evidence of linkage was also found to chromosomes 4, 5, and 13 (LOD scores >1.5). Our findings are consistent with those of other linkage studies that have reported linkage to chromosomes 5 and X.

Parkinson disease (PD) is the second most common neurodegenerative disorder, surpassed in frequency only by Alzheimer disease. Elsewhere we have reported linkage to chromosome 2q in a sample of sibling pairs with PD. We have now expanded our sample to include 150 families meeting our strictest diagnostic definition of verified PD. To further delineate the chromosome 2q linkage, we have performed analyses using only those pedigrees with the strongest family history of PD. Linkage analyses in this subset of 65 pedigrees generated a LOD score of 5.1, which was obtained using an autosomal dominant model of disease transmission. This result strongly suggests that variation in a gene on chromosome 2q36-37 contributes to PD susceptibility.

No abstract

Living to a late age without suffering any major health problems is a genetically influenced trait. To identify the genes contributing to this important phenotype, a 10 cM genome screen was performed in 95 pairs of male fraternal twins concordant for healthy aging. Individuals meeting these criteria were defined as those attaining the age of 70 free of cardiovascular disease (coronary surgery, diabetes, heart attack, and stroke) and prostate cancer. Six chromosomal regions were identified with logarithm of odds (LOD) scores greater than 1.2 (p<.01). A region on chromosome 4 at marker D4S1564 produced a LOD score of 1.67; this was the same marker previously linked to extreme longevity segregating as an autosomal dominant trait in centenarian families. Our results provide independent evidence that a locus on the long arm of chromosome 4 is associated with better physical aging and/or longevity.