Abstract
BackgroundMost twins after assisted reproductive technology (ART) are dizygotic. Analysis of dizygotic twin pairs is useful in assessing familial aggregation in the development of birth defects.MethodsUsing nationwide post-ART data from the Japan Society of Obstetrics and Gynecology, recurrence risk ratios (RRRs)—defined as probandwise concordance rates of birth defects in twins divided by the prevalence of birth defects in the general population—were calculated as indicators of familial aggregation. Birth defects were then reclassified according to the ICD-10 categories corresponding to codes Q00–Q99. From 2004 to 2009, there were 17 258 twin pregnancies.ResultsAt least 1 birth defect was noted in 236 twin pairs: 11 concordant and 225 discordant pairs. Regarding major organ systems, high probandwise concordance rates were observed for congenital malformations of eye, ear, face, and neck (11.8%), cleft lip and cleft palate (10.5%), congenital malformations of the nervous system (9.8%), and other congenital malformations of the digestive system (9.5%). High RRRs were observed for congenital malformations of eye, ear, face, and neck (RRR = 233), specifically other congenital malformations of the ear (RRR = 449); congenital malformations of the great arteries (RRR = 235), specifically those of the patent ductus arteriosus (RRR = 530); and for cleft lip and cleft palate (RRR = 208), specifically cleft palate with cleft lip (RRR = 609). The probandwise concordance rate of any birth defect (8.9%) was nearly identical to the approximated recurrence risk of sib-pairs (8.8%), which assumed multifactorial inheritance.ConclusionsThe present findings suggest that familial aggregation is a factor in some birth defects.
Highlights
According to data on assisted reproductive technology (ART) and vital statistics in Japan, the percentage of ART live births was 2.49% (26 680/1 070 035) in 2009, which indicates that ART is becoming widespread in Japan.[1]
Almost all medical institutions that perform ART are registered with the Japan Society of Obstetrics and Gynecology (JSOG)
Regarding classification by major organ system, relatively high probandwise concordance rates were observed for congenital malformations of eye, ear, face, and neck (11.8%), cleft lip and cleft palate (10.5%), congenital malformations of the nervous system (9.8%), and other congenital malformations of the digestive system (9.5%)
Summary
According to data on assisted reproductive technology (ART) and vital statistics in Japan, the percentage of ART live births was 2.49% (26 680/1 070 035) in 2009, which indicates that ART is becoming widespread in Japan.[1]. Zygosity determination of same-sex twin pairs is rarely performed at birth, and same-sex pairs are often regarded as monozygotic (MZ) twin pairs This assumption necessarily underestimates the resemblance of MZ pairs according to the proportion of dizygotic (DZ) pairs. It is important to compare the concordance rate of birth defects in DZ twin pairs (ie, siblings that develop together in the same womb)[2,3] with the prevalence of birth defects in the general population. The present study used nationwide data on ART to calculate the concordance rate of twin pairs and examine familial aggregation of birth defects. Methods: Using nationwide post-ART data from the Japan Society of Obstetrics and Gynecology, recurrence risk ratios (RRRs)—defined as probandwise concordance rates of birth defects in twins divided by the prevalence of birth defects in the general population—were calculated as indicators of familial aggregation. Conclusions: The present findings suggest that familial aggregation is a factor in some birth defects
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