title: Repeat instability in the 27-39 CAG range of the HD gene in the Venezuelan kindreds: Counseling implications.
abstract: The instability of the CAG repeat size of the HD gene when transmitted intergenerationally has critical implications for genetic counseling practices. In particular, CAG repeats between 27 and 35 have been the subject of debate based on small samples. To address this issue, we analyzed allelic instability in the Venezuelan HD kindreds, the largest and most informative families ascertained for HD. We identified 647 transmissions. Our results indicate that repeats in the 27-35 CAG range are highly stable. Out of 69 transmitted alleles in this range, none expand into any penetrant ranges. Contrastingly, 14% of alleles transmitted from the incompletely penetrant range (36-39 CAGs) expand into the completely penetrant range, characterized by alleles with 40 or more CAG repeats. At least 12 of the 534 transmissions from the completely penetrant range contract into the incompletely penetrant range of 36-39 CAG repeats. In these kindreds, none of the individuals with 27-39 CAGs were symptomatic, even though they ranged in age from 11 to 82 years. We expect these findings to be helpful in updating genetic counseling practices.
authors: Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK. deniseb@well.ox.ac.uk
authors: D
authors: D
authors: Brocklebank
authors: J
authors: J
authors: Gayán
authors: J M
authors: JM
authors: Andresen
authors: S A
authors: SA
authors: Roberts
authors: A B
authors: AB
authors: Young
authors: S R
authors: SR
authors: Snodgrass
authors: J B
authors: JB
authors: Penney
authors: M A
authors: MA
authors: Ramos-Arroyo
authors: J J
authors: JJ
authors: Cha
authors: H D
authors: HD
authors: Rosas
authors: S M
authors: SM
authors: Hersch
authors: A
authors: A
authors: Feigin
authors: S S
authors: SS
authors: Cherny
authors: N S
authors: NS
authors: Wexler
authors: D E
authors: DE
authors: Housman
authors: L R
authors: LR
authors: Cardon
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000368:Aged; D000369:Aged, 80 and over; D000483:Alleles; D002648:Child; D005190:Family; D005260:Female; D005817:Genetic Counseling; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D009419:Nerve Tissue Proteins / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics; D019683:Penetrance; D019680:Trinucleotide Repeat Expansion; D014687:Venezuela; D055815:Young Adult
chemical_list: C086055:HTT protein, human; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins