RESUMO
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.
Assuntos
Família , Aconselhamento Genético , Doença de Huntington/genética , Expansão das Repetições de Trinucleotídeos , Adolescente , Adulto , Idade de Início , Idoso , Idoso de 80 Anos ou mais , Alelos , Criança , Feminino , Humanos , Proteína Huntingtina , Masculino , Pessoa de Meia-Idade , Proteínas do Tecido Nervoso/genética , Proteínas Nucleares/genética , Penetrância , Venezuela , Adulto JovemRESUMO
We studied 65 Huntington's disease patients and 225 at-risk individuals over the past 4 years. The rate of decline of these untreated patients from Venezuela was similar to that seen in US patients who had received neuroleptic drugs. Chorea, oculomotor dysfunction, and dysdiadochokinesis were early symptoms; parkinsonian features and dystonia came later. Juvenile patients declined nearly twice as fast as adult-onset patients. No distinctive neurologic phenotypes were seen in children of two affected parents.