Letter: Congenital absence of vasa.

Although it is generally true that most male patients with cystic fibrosis 
are infertile due to congenital atresia or absence of the vasal 
structures, this finding is not invariable. Taussig et al. reported 2 
well-studied patients with cystic fibrosis who had normal semen analysis, and 
at this writing both have fathered children. A third patient with 
normal semen analysis also is known to us. In addition there 
are many instances of presumed but undocumented paternity in these patients. 
Cystic fibrosis centers estimate male fertility at 2 to 3 per 
cent; although low, this figure warrants semen analysis before assuming sterility. 
In view of this, we feel that the diagnosis of cystic 
fibrosis should be considered when the vasa are absent, but it 
is incorrect to exclude the diagnosis on the basis of palpable 
vasa. 