There are at least nine well-characterized syndactylous entities with subdivisions, the majority of which have non-syndromic nature. Syndactyly may segregate as an isolated clinical phenotype. On the minimal extreme, a milder phenotype may only be recognized by the alterations in interphalangeal creases and peculiarities in dermatoglyphics.
Syndactyly can be identified as partial or complete, cutaneous or bony, and involving only the phalanges or further extending up to metacarpal/metatarsal or carpal/tarsal levels, sometimes even proximating the distal end of forearm/foreleg.
The condition is so variable that the same individual may exhibit asymmetrical phenotypes in the upper and lower, and right and left limbs. Furthermore, inter- and intra-familial phenotypic variability is quite common. It may be unilateral or bilateral, and symmetrical or asymmetrical. A number of combinations are possible in which the adjacent fingers and/or toes remain connected by a web. 1, 2Ĭlinically syndactyly is one of the most heterogeneous developmental deformities known in the medical literature. It is one of the most common hereditary limb malformations depicting a prevalence of 3–10 in 10 000 births, though higher estimates ranging from 10–40/10 000 have been reported. Syndactyly (Greek Syn=together Dactylos=digit) is a digital malformation in which adjacent fingers and/or toes are webbed because they fail to separate during limb development. Despite considerable progress in the understanding of syndactyly at clinical and molecular levels, fundamental questions regarding the disturbed developmental mechanisms leading to fused digits, remain to be answered. In this communication, based on an overview of well-characterized isolated syndactylies, their cardinal phenotypes, inheritance patterns, and clinical and genetic heterogeneities, a ‘current classification scheme’ is presented. Whereas the underlying genes/mutations for types II-1, III, IV, V, and VII have been worked out, the etiology and molecular basis of the other syndactyly types remain unknown. Most of the syndactyly types are inherited as autosomal dominant but two autosomal recessive and an X-linked recessive entity have also been described. At least nine non-syndromic syndactylies with additional sub-types have been characterized. Even within a subject, phenotype can be unilateral or bilateral and symmetrical or asymmetrical. Syndactylies exhibit great inter- and intra-familial clinical variability. It may occur as an isolated entity or a component of more than 300 syndromic anomalies. Syndactyly is one of the most common hereditary limb malformations depicting the fusion of certain fingers and/or toes.
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