title: Caution regarding the interpretation of homoallelism in polyglutamine multiplex assays: a recommendation for confirmatory testing of homozygous alleles.
abstract: Spinocerebellar ataxia type 7 (SCA7) is an inherited dominant neurodegenerative disease caused by the expansion of a CAG repeat within the ATXN7 gene. Standard molecular diagnostic testing for SCA7 involves amplification of the region surrounding the CAG repeat via end-labeled PCR and subsequent capillary electrophoresis. In addition, multiplex methods exist that may be used to test for multiple polyglutamine spinocerebellar ataxias in a single assay. Herein, we used a SCA7 singleplex method to screen 111 individuals for whom the multiplex method detected a single normal allele. A total of six retested individuals (5.4%) were shown to have a pathogenic expansion at the ATXN7 locus. An additional triplet-primed PCR method was used to test the same cohort, and revealed no further disease-causing alleles. This study demonstrates the importance of using complementary methods to rule out apparent homoallelism during molecular testing for polyglutamine diseases.
authors.affiliation: Division of Human Genetics, the Department of Clinical Laboratory Sciences, Institute of Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa.
authors.forename: Danielle C
authors.initials: DC
authors.lastname: Smith
authors.forename: Alina
authors.initials: A
authors.lastname: Esterhuizen
authors.forename: Jacquie
authors.initials: J
authors.lastname: Greenberg
mesh_terms: D000293:Adolescent; D000483:Alleles; D000067719:Ataxin-7; D006720:Homozygote; D006801:Humans; D008297:Male; D058889:Molecular Typing / Q000379:methods; D009419:Nerve Tissue Proteins / Q000235:genetics; D010455:Peptides / Q000235:genetics*; D016133:Polymerase Chain Reaction / Q000379:methods; D017422:Sequence Analysis, DNA; D020754:Spinocerebellar Ataxias / Q000175:diagnosis* / Q000235:genetics*; D019680:Trinucleotide Repeat Expansion
chemical_list: C000593829:ATXN7 protein, human; D000067719:Ataxin-7; D009419:Nerve Tissue Proteins; D010455:Peptides; C097188:polyglutamine