Screening for the presence of FMR1 premutation alleles in women with parkinsonism

Abstract

Background: Fragile X-associated tremor/ataxia syndrome (FXTAS) is a progressive, late-onset neurodegenerative disease that affects older carriers of premutation (CGG) repeat expansions of the fragile X mental retardation 1 (FMR1) gene. Clinical features include intention tremor, gait ataxia, memory loss, peripheral neuropathy, autonomic dysfunction, and parkinsonism. The presence of parkinsonism in FXTAS raises the possibility that some individuals who have Parkinson disease are actually carriers of a premutation FMR1 allele.

Objective: To screen DNA samples from a large cohort of females with Parkinson disease for an excess of expanded alleles of the FMR1 gene.

Design and patients: We screened a cohort of 595 women with parkinsonism, the largest screening of a parkinsonism-associated group to date, for the presence of an FMR1 premutation allele (55-200 CGG repeats). The screening protocol uses an enhanced polymerase chain reaction method capable of flagging any FMR1 expanded CGG repeat in women as well as in men.

Setting: Diagnostic assessments were performed at an outpatient tertiary clinic (Parkinson Institute, Milan). Genotyping was conducted at the University of California, Davis.

Main outcome measures: CGG repeat number and clinical/neuroimaging assessments of patients with Parkinson disease were conducted. Two premutation carriers were identified.

Results: Two individuals possessed an FMR1 allele in the premutation range (CGG repeats: 30 and 75; 30 and 115). This carrier frequency (2 of 595 [0.34%]) is not significantly different from estimates of the allele frequency among women in the general population (0.4%-0.8%). Clinical and radiologic features of these 2 patients were similar to those of the general Parkinson disease population; however, 1 patient (115 CGG repeats) had a family history of 2 sons with the fragile X syndrome.

Conclusion: Screening of women within the parkinsonism clinical spectrum is unlikely to be productive in the absence of additional medical or family history suggestive of involvement of the FMR1 gene.