Spinocerebellar ataxia type 1 and type 3 (SCA1, SCA3) are autosomal dominant 
neurodegenerative disorders caused by expanded CAG trinucleotide repeats in 
novel genes. In our collective of SCA1 and SCA3 families, we observed distortion 
of the Mendelian 1:1 segregation of the disease. The mutated alleles were 
preferentially transmitted by female carriers in SCA3, whereas a gender effect 
on clinical features such as age of onset was not obvious. The mechanism 
underlying segregation distortion remains to be established.