A family with an atypical presentation of TBX3-related disorder.

Background: Ulnar mammary syndrome (UMS) is an autosomal dominant disorder caused by heterozygous pathogenic variants in the T-box transcription factor 3 (TBX3) gene. The phenotype is classically characterized by upper limb defects and apocrine/mammary gland hypoplasia. Endocrine abnormalities include hypogonadotropic hypogonadism (HH), partial growth hormone deficiency and dysmorphic features, while ectopic pituitary gland and various congenital anomalies have also been described. Here, we report a family with a unique clinical presentation.

Methods: Exome sequencing was performed for twin siblings with micropenis, neonatal hypogonadism, and congenital giant bladder diverticula.

Results: We identified a novel likely pathogenic heterozygous TBX3 variant c.844G>T; p.(Gly282Cys) inherited from the apparently unaffected mother. Reverse phenotyping confirmed that the mother and the twins had features suggestive of UMS spectrum. The mother had been diagnosed as having HH, with an hypoplastic pituitary gland. The physical examination revealed a bifid nasal tip and a bi-lobulated tongue tip typical for UMS with no apparent limb or mammary defects.

Discussion: This report extends the phenotype of the TBX3-related disorder to include HH and bladder anomalies without significant limb or mammary manifestations.