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Trinucleotide repeat analysis of Huntington's disease gene in Singapore
1DNA Diagnostic and Research Laboratory, Genetics Service, Department of Paediatric Medicine, KK Women's and Children's Hospital, 100 Bukit Timah Road, Singapore 229899. hylaw@kkh.com.sg
Introduction:
Huntington's disease (HD) is an inherited neurodegenerative disorder characterised by chorea and progressive dementia. The mutation causing the disease has been identified as an unstable expansion of a trinucleotide (CAG)n. We have assessed the (CAG)n repeats in the patients and controls in our population.
Materials And Methods:
Polymerase chain reactions (PCRs) for the repeat region were carried out for 116 individuals: 10 were asymptomatic at-risk members from 5 families; 53 symptomatic patients from various hospitals; and 53 normal unrelated Singaporeans. Estimation of the number of repeats was based on Metaphor gel electrophoresis, sizing using the GeneScan on ABI 310 Genetic Analyzer, and sequencing using the same equipment.
Results:
Metaphor gel sizing generally gives an over-estimation, and GeneScan gives an under-estimation of repeat numbers compared with sequencing which is the gold standard. Of the 63 patients and family members tested, 25 had one expanded allele of 40 to 54 CAG repeats and the other allele in the normal range of 15 to 30 repeats. One patient had an allele in the intermediate range (38).
Conclusion:
The range of CAG repeats in the normal and HD alleles in our population is similar to those reported elsewhere. An accurate sizing can only be obtained with sequencing. For allele sizes in the intermediate range (37-40), sequencing should be carried out to confirm the carrier status of a patient.