Is hemifacial microsomia linked to multiple maternities?

Hemifacial microsomia describes a congenital orofacial malformation in which there is insufficient or disrupted development of the mandible affecting one side of the face. The aetiology of this condition remains unclear, but it has been postulated that twins (predominantly monozygotic) are more liable to be affected than singletons. This study investigates the incidence of multiple births amongst a large number of affected individuals and their families. Data were collected on 145 individuals with hemifacial microsomia and microtia, using postal questionnaires and interviews in a hospital setting. These data were compared with the mean age-standardised twin maternity prevalence for England and Wales between 1975 and 1995 of 1.06% and the triplet maternity prevalence for England and Wales for 1995 of 0.034% (a multiple maternity being where more than one baby is born, either alive or stillborn). The prevalence of twin maternities amongst the affected individuals was 3.96% (P>0.05) and amongst their siblings it was 4.02% (P<0.02). There was also an excess of twins in the rest of the family groups, predominantly due to a stronger history of twinning on the maternal side. As there were more twins amongst the affected individuals than in the general population, it seems likely that whatever the aetiology of hemifacial microsomia and microtia, the presence of a co-twin (or co-triplets) may make the causal event, or series of causal events, more likely to occur. This study supports the hypothesis that hemifacial microsomia and microtia are in some way linked to multiple births. Analysis of this link may provide new directions for research into the aetiology of a variety of congenital defects.