Mesoaxial synostotic syndactyly with phalangeal reduction (MSSD): syndactyly type IX

Genetic determinants of syndactyly: perspectives on pathogenesis and diagnosis

The formation of the digits is a tightly regulated process. During embryogenesis, disturbance of genetic pathways in limb development could result in syndactyly; a common congenital malformation consisting of webbing in adjacent digits. Currently, there is a paucity of knowledge regarding the exact developmental mechanism leading to this condition. The best studied canonical interactions of Wingless‐type–Bone Morphogenic Protein–Fibroblast Growth Factor (WNT–BMP–FGF8), plays a role in the interdigital cell death (ICD) which is thought to be repressed in human syndactyly. Animal studies have displayed other pathways such as the Notch signaling, metalloprotease and non-canonical WNT-Planar cell polarity (PCP), to also contribute to failure of ICD, although less prominence has been given. The current diagnosis is based on a clinical evaluation followed by radiography when indicated, and surgical release of digits at 6 months of age is recommended. This review discusses the interactions repressing ICD in syndactyly, and characterizes genes associated with non-syndromic and selected syndromes involving syndactyly, according to the best studied canonical WNT-BMP-FGF interactions in humans. Additionally, the controversies regarding the current syndactyly classification and the effect of non-coding elements are evaluated, which to our knowledge has not been previously highlighted. The aim of the review is to better understand the developmental process leading to this condition.

An unusual association of ulnar hemimelia with mesoaxial synostotic syndactyly

Ulnar hemimelia, also referred to as post-axial longitudinal deficiency of the upper limb, is a very rare skeletal anomaly characterized by the partial or complete absence of the ulna. The majority of the reported cases are sporadic and more common in males. The disorder is mostly unilateral, right-sided and incomplete. A slight shortening of the forearm, radial bowing and ulnar-sided hand drift are the anomalies which often accompany ulnar hemimelia. Ulnar hemimelia may also be seen in association with complex wrist and hand anomalies. The absence of post-axial metacarpal and digital bones are frequent findings in patients with this rare disorder. Cases with additional digital abnormalities such as post-axial syndactyly and camptodactyly are also present in the literature. However, a case of ulnar hemimelia in association with mesoaxial synostotic syndactyly has never been reported to date.