Analysis of Repeat Expansion in HTT Gene in Families with Huntington’s Disease

Abstract

Huntington’s disease (HD) is a late-onset neurodegenerative disorder characterized by motor, cognitive and psychiatric abnormalities. HD is caused by repeat expansion in the huntingtin (HTT) gene located on chromosome 4p16.3. HD is frequently reported in Western populations, but there is a scarcity of studies from Pakistan. The present study aimed to analyze the clinical and genetic characteristics of HD in Pakistani families. For this study, three families with HD phenotype and healthy controls were recruited from different regions of Pakistan. The age of onset of HD in 8 patients of three families ranges from 20 to 49 years, except the single patient who presented juvenile-onset HD. Clinical features observed in these patients included chorea, tremors, bradykinesia, dystonia, facial dysmorphism, progressive dementia and low learning abilities. Brain magnetic resonance imaging (MRI) of 2 patients (H2-2, H3-1) presented severe striatum atrophy. Blood smear analysis was used to study acanthocytes in family H1 and H2 by light microscopy. The erythrocyte sedimentation rate (ESR) results of family H1 and H2 demonstrated a reduced sedimentation rate in the affected individuals as compared with healthy individuals. The average number of CAG repeats in the HTT gene of affected individuals was found to be between 40 to 70 CAGs and lies in the pathogenic range. The expanded and normal alleles of selected families were also confirmed by Sanger sequencing. One patient from family H2 with juvenile HD has 67 CAG repeats. Two members of family H1 have 44 CAG repeats in both alleles and their current ages were 13 and 24 years. Whereas the analysis of CAG repeats in normal controls by 2.5% agarose gel showed a range from 18 to 22. An inverse correlation between the age of onset of HD and CAG repeats was observed in our study. This study represents the first molecular characterization of HD in stani families and provides an initial estimation of repeat size in HD patients and healthy controls.