Split hand/foot malformation (SHFM) is a congenital limb disorder resulting in the absence of some fingers or toes, a deep cleft in the center of the hand or foot giving a ‘lobster claw’ like appearance, and the fusion of the remaining digits, also known as syndactyly. The condition is highly variable, even between affected members of the same family. The overall prevalence of SHFM is about 1 in 18,000 live births, however SHFM6 is a rare subset with only a handful of cases reported thus far. SHFM does not have a gender bias; it affects males and females equally.
Diagnosis is made based on clinical features at birth and X-ray imaging studies. Identification of the underlying gene mutation is beneficial in providing families with genetic counselling. While there is no cure for the disorder, symptomatic and supportive therapies help improve quality of life. Reconstructive surgeries and prosthetics are viable treatment options.
The disorder follows an autosomal recessive pattern of inheritance and is caused by homozygous mutations in the WNT10B gene. This gene encodes a secreted signaling protein that mediates the canonical Wnt signaling pathway and thereby plays a role in several developmental processes. These include the regulation of adipocyte, chondrocyte and epithelial cell differentiation, hematopoietic stem cell proliferation, cell cycle arrest and cell fate commitment, apoptosis, skeletal muscle fiber development and bone trabecula formation. So far only a handful of mutations in the WNT10B gene, namely duplications and missense variants, have been linked to the disorder.
Monies et al. (2017) illustrated the genomic landscape of Saudi Arabia based on the findings of 1000 diagnostic panels and exomes. One patient, an 8-year-old female from a consanguineous family, presented with feet ectrodactyly, thumb polydactyly, left index camptodactyly and 2 missing digits in both feet. She also exhibited facial dysmorphic features such as hypertelorism and a broad nasal bridge. However, she had normal development. Using a multigene panel for dysmorphology/skeletal dysplasia, a homozygous mutation (c.338-1G>C) was identified in exon 4 of the patient’s WNT10B gene. Given the atypical presentation of the patient, this case helped in the phenotypic expansion of the disorder.
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