Complex segregation analysis was conducted in a sample of 171 pedigrees collected through
probands affected by non-syndromic dysplasia of the hip (CDH) treated in Ferrara's CDH Centre in
the period 1991–6. The analysis favoured a two-locus model, in which the accepted segregation model
at the major locus was compatible with recessive transmission, with a gene frequency of the
deleterious allele of around 0.20. For the other locus, among the Mendelian hypotheses tested, the
recessive model turned out to be the most parsimonious. When ultrasonographic level was examined
as an indication of severity, a significant improvement in the fit of the model was observed, giving
clear evidence that information on the severity of CDH is important for a better definition of the
hereditary transmission model.