ABSTRACT
AIMS: Most patients (98%) with Friedreich's ataxia (FRDA) are homozygous for the GAA repeat expansion in FXN. Only a few compound heterozygous patients with an expanded repeat on one allele and a point mutation or an intragenic FXN deletion on the other allele are described. In a minority of the patients only a heterozygous pattern of the repeat expansion can be detected. Using array analysis after GAA repeat expansion testing, we identified a FRDA patient who is compound heterozygous for an expanded GAA repeat and a complete FXN deletion. Since not only repeat expansions and point mutations, but also large rearrangements can be the underlying cause of FRDA, a quantitative test should also be performed in case a patient shows only one allele with an expanded GAA repeat in FXN.
Subject(s)
Friedreich Ataxia/genetics , Gene Deletion , Heterozygote , Iron-Binding Proteins/genetics , Trinucleotide Repeat Expansion/genetics , Adult , Female , Humans , Male , Pedigree , FrataxinABSTRACT
PURPOSE: Univerricht-Lundborg disease (ULD), with its major symptom of action myoclonus, is supposed to be very rare in the Netherlands and western Europe. We hypothesized that the syndrome may be underdiagnosed in patients with myoclonus epilepsy. METHODS: Mutation analysis of the cystatin B gene was performed in 21 cases with uncontrolled myoclonus. RESULTS: Seven of the 21 evaluated cases carried mutations in the cystatin B gene. Diagnosis of ULD was made with a mean delay of 20 years from symptom onset. CONCLUSIONS: This study from a country without previous reports of ULD suggests that underdiagnosis of the syndrome is likely. These findings also indicate that persons with juvenile-onset myoclonus epilepsy with action myoclonus should be analyzed for ULD.
