A de novo TBX3 mutation presenting as dorsalization of the little fingers: A forme fruste phenotype of ulnar-mammary syndrome.

Ulnar-mammary syndrome (UMS) is a rare syndromic limb malformation caused by heterozygous mutations in TBX3. The name highlights the two commonly involved body parts i.e. mammary gland and ulnar ray of the upper limbs, although a more extensive systemic involvement is also known to occur. Here, we report the surprising finding of a patient with a de novo mutation in TBX3 whose clinical presentation is limited to dorsalization of both little fingers and slightly deep 4th web spaces. We review the literature to confirm that this should be considered as a forme fruste phenotype of UMS.