Clinical manifestations of homozygote allele carriers in Huntington disease
- 30 April 2019
- journal article
- research article
- Published by Ovid Technologies (Wolters Kluwer Health) in Neurology
- Vol. 92 (18), E2101-E2108
- https://doi.org/10.1212/wnl.0000000000007147
Abstract
Objective Because patients homozygous for Huntington disease (HD) receive the gain-of-function mutation in a double dose, one would expect a more toxic effect in homozygotes than in heterozygotes. Our aim was to investigate the phenotypic differences between homozygotes with both alleles ≥36 CAG repeats and heterozygotes with 1 allele ≥36 CAG repeats. Methods This was an international, longitudinal, case-control study (European Huntington's Disease Network Registry database). Baseline and longitudinal total functional capacity, motor, cognitive, and behavioral scores of the Unified Huntington's Disease Rating Scale (UHDRS) were compared between homozygotes and heterozygotes. Four-year follow-up data were analyzed using longitudinal mixed-effects models. To estimate the association of age at onset with the length of the shorter and larger allele in homozygotes and heterozygotes, regression analysis was applied. Results Of 10,921 participants with HD (5,777 female [52.9%] and 5,138 male [47.0%]) with a mean age of 55.1 ± 14.1 years, 28 homozygotes (0.3%) and 10,893 (99.7%) heterozygotes were identified. After correcting for multiple comparisons, homozygotes and heterozygotes had similar age at onset and UHDRS scores and disease progression. In the multivariate linear regression analysis, the longer allele was the most contributing factor to decreased age at HD onset in the homozygotes (p < 0.0001) and heterozygotes (p < 0.0001). Conclusions CAG repeat expansion on both alleles of the HTT gene is infrequent. Age at onset, HD phenotype, and disease progression do not significantly differ between homozygotes and heterozygotes, indicating similar effect on the mutant protein. Classification of evidence This study provides Class II evidence that age at onset, the motor phenotype and rate of motor decline, and symptoms and signs progression is similar in homozygotes compared to heterozygotes.This publication has 27 references indexed in Scilit:
- CAG repeat expansion in Huntington disease determines age at onset in a fully dominant fashionNeurology, 2012
- Observing Huntington’s Disease: the European Huntington’s Disease Network’s REGISTRYPLoS Currents, 2011
- Hypothalamic–endocrine aspects in Huntington's diseaseEuropean Journal of Neuroscience, 2006
- Levels of mutant huntingtin influence the phenotypic severity of Huntington disease in YAC128 mouse modelsNeurobiology of Disease, 2006
- Severe ultrastructural mitochondrial changes in lymphoblasts homozygous for Huntington disease mutationMechanisms of Ageing and Development, 2006
- No post-genetics era in human disease researchNature Reviews Genetics, 2002
- Self-assembly of polyglutamine-containing huntingtin fragments into amyloid-like fibrils: Implications for Huntington’s disease pathologyProceedings of the National Academy of Sciences of the United States of America, 1999
- Unified Huntington's disease rating scale: Reliability and consistencyMovement Disorders, 1996
- A Worldwide Study of the Huntington's Disease Mutation: The Sensitivity and Specificity of Measuring CAG RepeatsThe New England Journal of Medicine, 1994
- Homozygotes for Huntington's diseaseNature, 1987