Tryptophan hydroxylase gene polymorphism (A218C) and idiopathic recurrent miscarriage. 
To investigate the frequency of a polymorphism in intron 7 of the tryptophan hydroxylase gene among women with idiopathic recurrent miscarriage and healthy controls.  In a case control study, we studied 125 women with a history of three or more consecutive pregnancy losses before 20 weeks' gestation and 137 healthy controls with at least two live births and no history of pregnancy loss.  Peripheral venous puncture, DNA extraction, and polymerase chain reaction followed by restriction fragment length polymorphism analysis were used to genotype women for the presence of the A218C polymorphism in intron 7 of the tryptophan hydroxylase gene.  Allele frequencies among women with idiopathic recurrent miscarriage and controls were 32.4% and 38.7%, respectively, for allele A (wild type) and 67.6% and 61.3%, respectively, for allele C (mutant).  No association between the presence of allele C and idiopathic recurrent miscarriage was found (P = .3; odds ratio 1.31; 95% confidence interval 0.93, 1.87).  Genotype frequencies also were not significantly different between the study group (C/C: 44.8%; A/C: 45.6%; A/A: 9.6%) and the control group (C/C: 37.2%; A/C: 48.2%; A/A: 14.6%; P = .2).  Between women with primary and women with secondary idiopathic recurrent miscarriage, no statistically significant differences with respect to allele frequencies were observed (63% vs 62% for allele C and 31% vs 38% for allele A; P = .3).  The A218C polymorphism in intron 7 of the tryptophan hydroxylase gene is not associated with idiopathic recurrent miscarriage.