The study relates to congenital limb reduction defects (CLRDs) in twin
s from a 10-year-period (1975-1984) and is based on cases from the Hun
garian Congenital Abnormality Registry. In order to clarify the respec
tive contributions of genetic and environmental factors to CLRDs and t
he role of causal factors in common with twinning, the occurrence of C
LRDs in twins was studied. In eight multiple CLRD twin cases (i.e. tho
se with additional non-limb malformations), one monozygous concordant
and one semi-concordant twin pair was found, indicating that genetic f
actors play a limited role in pathogenesis. There is no correlation be
tween twinning and isolated CLRDs. Frequency of CLRDs in general was n
o higher in twins than in all births, although there was a non-signifi
cantly higher twinning rate in multiple CLRD cases. Twins with CLRDs w
ere more often male? especially in multiple cases. Conclusion There ma
y be a relationship between twinning and congenital abnormalities, but
twinning is not a major factor contributing to CLRD cases.