Inbreeding in recessive diseases.

The consanguinity of parents (born in France) of individuals who have a 
recessive disease has been studied. The frequency of first cousin marriages 
is less than 0.2% in the general French population. Among the 
parents of affected individuals the following frequencies of first cousin matings 
were observed: cystic fibrosis: 1.4% cystinosis: 7.1% nephronophtisis: 5.6% spinal muscular 
atrophy: 4.5% albinism: 5.0% achromatopsia: 12.5% (Albinism and spinal muscular atrophy 
are heterogeneous conditions). The increase in the frequency of first cousin 
marriage relative to that of the general population is much greater, 
as expected, in cystinosis, which is a rare disease, than in 
cystic fibrosis, which is the most frequent recessive disorder in France. 
Inbreeding in cystinosis and cystic fibrosis was also studied by computing 
the distance between parental birth places. This distance is smaller in 
cystinosis than in cystic fibrosis. 