Studies on herediatary spherocytosis in Iceland.

Thirty members with typical hereditary spherocytosis (HS) and over 90 apparently unaffected members belonging to 12 families have been studied. Splenectomy has been performed on 22 HS patients. Of nine HS individuals, who had not undergone surgical treatment in 1957, four suffered from temporary severe anaemia, presumably due to aplastic crisis associated with influenza. One of them died, a male 18 years of age. Pedigree studies on one of the families indicate that the HS gene or genes have been transmitted through six generations over the past 200 years. Marked deficiency in the number of affected compared with the apparently unaffected members in the HS families is present. The most striking example of uneven genetic ratio is a sibship of 15 members investigated haematologically, with one suffering from typical HS. Much reduced penetration of the HS gene or the presence of the socalled "mild form" is upheld as the main explanation for the unevenness in the genetic ratio. However, families are also present in which abortions and death at an early age indicated that selection against the affected could also disturb the genetic ratio in HS families.