Tibia, Hypoplasia or Aplasia of, with Polydactyly

Alternative Names

  • THYP
  • Tibial Hemimelia-Polydactyly-Triphalangeal-Thumbs with Fibular Dimelia
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WHO-ICD-10 version:2010

Congenital malformations, deformations and chromosomal abnormalities

Congenital malformations and deformations of the musculoskeletal system

OMIM Number

188740

Mode of Inheritance

Autosomal dominant

Gene Map Locus

7q36.3

Description

Hypoplasia or aplasia of the tibia with polydactyly (THYP) is an extremely rare disorder, characterized by under-development of both the shank bones (tibial hypoplasia) and the presence of extra fingers and/or toes (polydactyly). Patients may also show some additional features, including thickened and/or duplicated fibula, hand syndactyly, and triphalangeal thumb. Only very few cases of this congenital malformation syndrome are known worldwide, and very little information is available.

Mutations in the SHH (sonic hedgehog signaling molecule) regulatory element of the LMBR1 gene is known cause THYP. The few families in which the disease has been described, it appears to follow an autosomal dominant mode of inheritance.

Epidemiology in the Arab World

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Other Reports

Kuwait

Al-Awadi et al. (1987) described an Arab family with 16 members in four generations with either bilateral syndactyly or postaxial polydactyly, or both. The proband was a 5-year old boy born to consanguineous parents. He was born with bilateral postaxial polydactyly of both hands, with some fingers showing clinodactyly and continuous syndactyly. Some of the toes showed postaxial polysyndactyly, and partial cutaneous syndactyly. Both legs were short and bowed, and radiographic analysis revealed hypoplastic tibia with mild involvement of the fibula. There were no craniofacial abnormalities or other organ involvement. The 15 other affected members included the boy's elder sister and father. A sister had polysyndactyly. The mother had only cutaneous syndactyly, but her grandfather had polysyndactyly and another relative of hers had either syndactyly or polysyndactyly. Pedigree analysis suggested that the great-grandfather of the proband transmitted the polysyndactyly down through this inbred family in an autosomal dominant manner. Interestingly, none of the other affected members had tibial hypoplasia. Al-Awadi et al. (1987) opined that this was a new syndrome of bilateral tibial hypoplasia with postaxial poysyndactyly.

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