Clinical genetics / edited by Arnold Sorsby.

Date:
1953
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Clinical genetics / edited by Arnold Sorsby. Source: Wellcome Collection.

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    THE UPPER EXTREMITIES or parts of a limb, to bifurcation of a distal phalanx, or a mere fleshy protrusion (pedunculated post-minimus). In hexadactyly, the most common form, the accessory finger may be radial or ulnar in position. All possible inter-gradations may exist. Syndactyly and other congenital anomalies may be associated findings, but on the whole, the affected individuals are generally normal in every other respect. Syndactyly .—-iÜQxt a fusion of the digits can exist in any degree from a cutaneous webbing to synostosis of the phalanges. The webbing usually involves the second and third digits. Polydactyly, brachydactyly, and other congenital anomalies of development are frequently associated. The term zygodactyly has been suggested for the cutaneous webbing between the second and third toes with no change in the bone structure. The term syndactyly is employed for actual bony fusion. There is a greater incidence for the male sex. Any race may be affected. Hyperphalangy of the thumb.—Extra phalanges may occur and are especially common in the thumb. Hyperphalangism of the fingers appeared associated with brachydactyly in Unterrichter's family (1934). The hand Split hand {lobster hand).—Birch-Jensen (1949) describes two types: (1) complete or partial absence of one or more of the three central rays and the two radial rays; and (2) is considered as a particularly pronounced degree of type 1, the radial rays being cut off proximally so that there is no cleft formation. He further subdivided type 1 into subgroup (a) characterized by a more or less pronounced cone-shaped cleft formation tapering proximally. The hand is divided into two parts which are moved toward each other—lobster-claws. Syndactylism of the fingers of each side of the cleft is a frequent association. Polydactylism may also be associated with syndactylism. A marked range of variability may exist both interfamilially and intrafamilially (Fig. 148). Atypical split hand.—According to Birch-Jensen this shows characterized by absence of some of the central rays, but differs from the typical spht hand in that there is a reduction of the remaining rays. The trait is usually unilateral. The Danish incidence at birth was estimated to be 1 in 150,000. Syndactyhsm is a frequently associated congenital anomaly. Ectrodactylism.—Birch-Jensen uses this term for cases involving total or partial absence of rays where there is no reduction of the remaining bony parts. The variability of ectrodactylism can include partial absence of fingers, or total absence of fingers, hypophalangy, and polydactyhsm. Radial defects Defects of the radius and radial rays are often present in the same individual. Birch-Jensen stressed the frequency of unilateral involvement, and the frequent association with other widespread congenital anomalies. He gives the incidence at 1 : 30,000 births. 269