Image B is consistent for postaxial polydactyly, which is more prevalent in patients of African-American ancestry.
The cohort study by Woolf found the incidence of postaxial polydactyly in African americans is 12.42 per 1,000 (1.2%) compared to the Caucasian incidence of 0.91 per 1,000 (0.09%). If postaxial polydactyly is found in a patient of Caucasian ancestry then further workup for underlying syndromes (chondroectodermal dysplasia or Ellis-van Creveld syndrome) is needed.
The article by Orioli is a case-control study that hypothesizes that a sex-linked recessive modifier gene occurs more frequently in African americans and this gene then promotes the autosomal dominant polydactyly gene.
Incorrect Answers: Constriction band syndrome or amniotic band syndrome is a type of pseudosyndactyly (Figure A) and is not the result of failure of differentiation during embryogenesis, but a result of injury by bands after the fingers are formed. Preaxial polydactyly (Figure C) is more common in caucasians and is usually sporadic except for triphalangism which is associated with Holt-Oram and Fanconi's Anemia. Syndactyly (Figure D) is defined as an abnormal interconnection between adjacent digits and syndactyly variations are associated with Apert syndrome and Poland syndrome. Macrodactyly (Figure E) represents overgrowth of all structures of the involved digit and is associated with neurofibromatosis and Klippel-Trenaunay-Weber syndrome.
Ezaki M, Kay SPJ, Light TR, Tonkin MA, Wood VE, Dobyns JH. Congenital hand deformities, In: Green DP, Hotchkiss RN, Pederson WC, eds. Green's Operative Hand Surgery, 4th ed. New York, NY: Churchill Livingstone; 1999:325-551
Orioli IM. Segregation distortion in the offspring of Afro-American fathers with postaxial polydactyly. Am J Hum Genet. 1995 May;56(5):1207-11.
PMID:7726178 (Link to Abstract)
Woolf CM, Myrianthopoulos NC. Polydactyly in American Negroes and Whites. Am J Hum Genet. 1973 Jul;25(4):397-404.
PMID:4351996 (Link to Abstract)