Split hand is an inherited developmental abnormality resulting in malformed or absent fingers and/or toes; it may affect only one hand or foot or all four limbs. The condition, formerly called lobster claw syndrome, is also known as split hand/foot malformation (SHFM) or ectrodactyly [Wikipedia]. In some families it is an autosomal dominant condition, but in others it can skip several generations before another child is affected.
In the past, amputation of the affected digits was considered appropriate when an infant was born with one split hand, but the digits are useful if left in place. Current treatment may include surgery to fuse or separate digits, particularly of the feet (to enable the person to fit into regular shoes and/or walk normally), or a prosthesis to minimize the unusual appearance of an affected hand. A microsurgeon may be able to transfer a child's toes to a hand that has only one digit.
People with ectrodactyly, such as the actress and former television anchor Bree Walker, may be normal in every other way. [] [] In some cases there are additional limb defects, such as absent tibias. Some forms of SFHM are syndromic, meaning that other abnormalities are also present (for example, sensorineural hearing loss, eye defects, or microcephaly).
Ultrasound can diagnose the presence of ectrodactyly, but because split hand can be caused by many different mutations, it is not possible to predict whether a particular fetus will have other developmental problems that appear later. A research program on families affected by SHFM is in progress at the [Greenwood Genetic Center of South Carolina].
Several chromosomal regions have been implicated in split hand. SNPs and genes known to be involved include:
- rs1124110, a SNP in the GALNT2 gene
- When caused by rs1124110, split hand is considered an autosomal dominant disorder with low penetrance. Most carriers of the risk allele are normal, and homozygotes (who carry two copies of the risk allele) may be normal as well. An affected person may have one split hand or foot and three normal limbs; this person is likely to be normal in every other way.
- Another gene in addition to GALNT2 may be involved in causing split hand in families with skipped generations between affected people.
- rs1124110 is related to split hand/foot malformation with long bone deficiency type 1 (SHFLD1). OMIM
- TP63 or p63 (the tumor protein p63 gene)
- The p63 gene is involved in apoptosis, a process required in the development of the hands and feet. OMIM
- Several mutations in the p63 gene appear to cause ectrodactyly, ectodermal, dysplasia, and cleft lip/palate syndrome 3 (EEC3), a dominant disorder. [OMIM]