HLA or HLA-linked genes reduce birthweight in families affected by idiopathic recurrent abortion

HLA typing was performed in 49 families, each containing at least one woman with a history of unexplained recurrent spontaneous abortion (RSA), and reproductive histories were recorded for the siblings. Abortion rate in sisters sharing two HLA haplotypes with the proband was significantly (p less than 0.01) increased, whereas abortion rates of brothers' wives seemed independent of the brothers' degree of HLA sharing with the proband. Birthweights of offspring of both the sisters and the brothers decreased with increasing HLA haplotype identity between the sibling and the proband (p = 0.05). The mean birthweight of infants of siblings sharing both parental haplotypes with the proband was 3158 g which was significantly (p less than 0.02) less than the average birthweight in Denmark (3417 g). Significantly (p less than 0.05) decreased mean birthweight in infants of brothers who were HLA-identical with the proband suggested that the disposition to growth retardation could be inherited with HLA also through the male gametes. It has been shown that, in their few successful pregnancies, women with RSA bear infants with a birthweight which is approximately 300 g less than normal. The present study demonstrated that the two obstetrical conditions, RSA and retarded fetal growth, share common genetic markers: HLA. It is suggested that HLA or HLA-linked genes causing growth retardation in fetuses are part of the putative complex of genes involved in the pathogenesis of recurrent abortion.