Analysis of segregation patterns in Machado-Joseph disease pedigrees.
Machado-Joseph disease (MJD), also known as spinocerebellar ataxia type 3 (SCA3), is an autosomal dominant neurodegenerative disorder of late onset, which is considered the most common form of SCA worldwide. The main goal of this study was to investigate the presence of segregation ratio distortion (SRD) during transmissions of ATXN3 alleles by MJD patients, evaluating the putative role of SRD in the epidemiological representation of the disease. Sixty-two complete sibships, each with one clinically affected parent, totalling 330 transmissions were selected according to defined criteria and used for segregation analysis. Onset data from MJD patients with Azorean origin was used for residual risk estimates according to different ages. Residual risk values were applied to unaffected offspring to calculate the probability of inheriting the expanded allele. The proportion of offspring that received the expanded or the normal allele from the affected parent was calculated to determine the presence of SRD during transmissions of ATXN3 alleles by MJD patients. Segregation of ATXN3 alleles was in accordance with the expected Mendelian proportions (chi (2) = 0.982, P = 0.322). However, there was a tendency favouring the transmission of the normal alleles. Thus, SRD is not a potential mechanism on the basis of MJD epidemiological representation.
Bettencourt
Conceição
C
Center of Research in Natural Resources (CIRN) and Department of Biology, University of the Azores, Rua Mãe de Deus, Apartado 1422, 9501-801, Ponta Delgada, Azores, Portugal. mcbettencourt@uac.pt.
Santos
Cristina
C
Center of Research in Natural Resources (CIRN) and Department of Biology, University of the Azores, Rua Mãe de Deus, Apartado 1422, 9501-801, Ponta Delgada, Azores, Portugal.|Biological Anthropology Unit, Department BABVE, Faculty of Biosciences, Autonomous University of Barcelona, Bellaterra, Barcelona, Spain.
Kay
Teresa
T
Department of Clinical Genetics, Hospital of D. Estefania, Lisbon, Portugal.
Vasconcelos
João
J
Department of Neurology, Hospital of Divino Espirito Santo, Ponta Delgada, Portugal.
Lima
Manuela
M
Center of Research in Natural Resources (CIRN) and Department of Biology, University of the Azores, Rua Mãe de Deus, Apartado 1422, 9501-801, Ponta Delgada, Azores, Portugal.
D000293:Adolescent; D000328:Adult; D000368:Aged; D000483:Alleles; D000067699:Ataxin-3; D002648:Child; D002675:Child, Preschool; D020090:Chromosome Segregation / Q000235:genetics*; D005260:Female; D006801:Humans; D017827:Machado-Joseph Disease / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D009419:Nerve Tissue Proteins / Q000235:genetics*; D009687:Nuclear Proteins / Q000235:genetics*; D010375:Pedigree; D012097:Repressor Proteins / Q000235:genetics*
D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D012097:Repressor Proteins; C092341:ATXN3 protein, human; D000067699:Ataxin-3