The study relates to congenital limb reduction defects (CLRDs) in twins from a 10-year-period (1975-1984) and is based on cases from the Hungarian Congenital Abnormality Registry. In order to clarify the respective contributions of genetic and environmental factors to CLRDs and the role of causal factors in common with twinning, the occurrence of CLRDs in twins was studied. In eight multiple CLRD twin cases (i.e. those with additional non-limb malformations), one monozygous concordant and one semi-concordant twin pair was found, indicating that genetic factors play a limited role in pathogenesis. There is no correlation between twinning and isolated CLRDs. Frequency of CLRDs in general was no higher in twins than in all births, although there was a non-significantly higher twinning rate in multiple CLRD cases. Twins with CLRDs were more often male, especially in multiple cases.
Conclusion: There may be a relationship between twinning and congenital abnormalities, but twinning is not a major factor contributing to CLRD cases.