Novel premature termination codon in the FOXP3 gene as the cause of familial hydrops fetalis in males.

A 19-year-old, G1P0, pregnant person was referred at 20w2d gestation for evaluation due to non-immune hydrops fetalis (NIHF), which was confirmed at the time of evaluation. Amniocentesis was performed at 20 w4d, and FISH, karyotype, chromosomal microarray, and exome sequencing (ES) were ordered. Trio ES identified a novel hemizygous c.142 C > T (p.Arg48*; maternally inherited) variant in the FOXP3 gene, resulting in a premature termination codon and establishing the diagnosis of immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome. Intrauterine fetal demise (IUFD) was diagnosed at 21w3d. CVS was performed at 12w1d in a subsequent pregnancy (male fetus) and the known familial variant was identified. NIHF was identified at 18w1d. Ultrasound at 19w2d revealed IUFD. This is the first report of this variant in a diagnosis of IPEX syndrome, presenting with NIHF and male fetal demise. Genotype-phenotype correlations are not available in many cases of IPEX syndrome, as the same genotype can be present with variable severity in different individuals. Given the near identical presentations in this family, we anticipate a more severe phenotype with this variant. We propose a novel variant resulting in an early premature termination codon as an explanation for the severe presentation of IPEX syndrome in two successive fetuses in this family.