Machado-Joseph disease enhances genetic fitness: a comparison between affected and unaffected women and between MJD and the general population.
BACKGROUND
Machado-Joseph disease (MJD SCA3), a spinocerebellar ataxia related to expansion of a CAG tract, has already been related to anticipation and meiotic drift. However, fitness of MJD carriers has been little studied.


OBJECTIVE
To analyze genetic fitness of MJD patients, comparing them to their unaffected relatives and to the general population (GP) of origin.


METHODS
182 informants, belonging to 82 MJD families, agreed to participate in the study. Informants supplied data about 828 MJD patients. Number of children (NC), gender, age, school attainment, menarche and menopause were compared between general and emeritus (older than 45 years of age or deceased) groups.


RESULTS
Mean NC of the GP and of MJD patients were respectively 1.90 and 2.93+/-2.3 (p = 0.0037). Comparisons within families also showed differences: the mean NC of unaffected and affected emeritus MJD women were, respectively, 2.68 and 3.89 (p = 0.0037). Affected MJD women had earlier mean ages at the delivery of their first child and menopause (p < 0.011 and 0.07, respectively). Among affected women those who did not have children had larger CAG tracts than those who had children (p < 0.05).


CONCLUSIONS
MJD enhances the fitness of its carriers, and this phenomenon seems to have a biological basis.
Department of Genetics and Molecular Biology, Universidade Federal do Rio Grande do Sul, Brazil.
P R
PR
Prestes
M L
ML
Saraiva-Pereira
I
I
Silveira
J
J
Sequeiros
L B
LB
Jardim
D017668:Age of Onset; D001938:Brazil / Q000453:epidemiology; D016022:Case-Control Studies; D002648:Child; D015331:Cohort Studies; D005260:Female; D006579:Heterozygote; D006801:Humans; D017827:Machado-Joseph Disease / Q000453:epidemiology / Q000235:genetics* / Q000473:pathology; D044382:Population Groups; D015995:Prevalence