Triphalangeal thumb-polysyndactyly syndrome

Triphalangeal thumb-polysyndactyly syndrome (TPTPS), also known as preaxial polydactyly type II or polysyndactyly with triphalangeal thumb, is a rare congenital limb malformation characterized by the presence of a triphalangeal thumb (a thumb with three phalanges instead of the normal two, giving it a finger-like appearance) combined with preaxial polydactyly (extra digits on the thumb side of the hand) and variable syndactyly (fusion of digits). The condition primarily affects the skeletal and musculoskeletal systems, specifically the hands and sometimes the feet. The thumbs may appear long and finger-like due to the extra phalanx, and in some cases, affected individuals may have duplicated thumbs or additional preaxial digits. Foot involvement can include preaxial polydactyly of the toes and syndactyly. The severity and specific features can vary considerably, even among members of the same family. This syndrome is caused by mutations in a regulatory region (the ZRS, or zone of polarizing activity regulatory sequence) located within intron 5 of the LMBR1 gene on chromosome 7q36. This regulatory element controls the expression of the SHH (Sonic Hedgehog) gene, which plays a critical role in limb patterning during embryonic development. Point mutations or duplications in this region lead to ectopic expression of SHH in the anterior limb bud, resulting in the characteristic preaxial limb anomalies. Treatment is primarily surgical and is tailored to the specific anatomical abnormalities present in each individual. Surgical correction may include removal of extra digits (polydactyly reduction), separation of fused digits (syndactyly release), and reconstruction of the thumb to improve function and appearance. Occupational therapy may be recommended following surgery to optimize hand function. Genetic counseling is advised for affected families given the autosomal dominant inheritance pattern. The prognosis is generally good, as the condition does not typically affect other organ systems or life expectancy, and surgical outcomes are usually favorable for improving hand function.

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