Esther Cubo1, Saul-Indra Martinez-Horta2, Frederic Sampedro Santalo2, Asunción Martínez Descalls2, Sara Calvo2, Cecilia Gil-Polo2, Ignacio Muñoz2, Katia Llano2, Natividad Mariscal2, Dolores Diaz2, Aranzazu Gutierrez2, Laura Aguado2, María A Ramos-Arroyo2. 1. From the Neurology Department (E.C., C.G.-P., I.M., K.L., N.M., D.D., A.G., L.A.) and Research Unit (S.C.), Hospital Universitario Burgos; Movement Disorders Unit, Neurology Department (S.-I.M.-H., F.S.S.), Hospital de La Santa Creu I Sant Pau, Barcelona; Centro de Investigación en Red-Enfermedades Neurodegenerativas (CIBERNED) (S.-I.M.-H., F.S.S.), Madrid; Neurology Department (A.M.D.), Fundación Jiménez Diez, Madrid; and Genetic Department (M.A.R.-A.), Complejo Hospitalario de Navarra, Pamplona, Spain. mcubo@saludcastillayleon.es. 2. From the Neurology Department (E.C., C.G.-P., I.M., K.L., N.M., D.D., A.G., L.A.) and Research Unit (S.C.), Hospital Universitario Burgos; Movement Disorders Unit, Neurology Department (S.-I.M.-H., F.S.S.), Hospital de La Santa Creu I Sant Pau, Barcelona; Centro de Investigación en Red-Enfermedades Neurodegenerativas (CIBERNED) (S.-I.M.-H., F.S.S.), Madrid; Neurology Department (A.M.D.), Fundación Jiménez Diez, Madrid; and Genetic Department (M.A.R.-A.), Complejo Hospitalario de Navarra, Pamplona, Spain.
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.
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.
Authors: Roy Jung; Yejin Lee; Douglas Barker; Kevin Correia; Baehyun Shin; Jacob Loupe; Ryan L Collins; Diane Lucente; Jayla Ruliera; Tammy Gillis; Jayalakshmi S Mysore; Lance Rodan; Jonathan Picker; Jong-Min Lee; David Howland; Ramee Lee; Seung Kwak; Marcy E MacDonald; James F Gusella; Ihn Sik Seong Journal: Hum Mol Genet Date: 2021-04-26 Impact factor: 6.150