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Polydactyly in British Columbia, 1964-1967 Jones, Daryl Christine


The British Columbia [B.C.] Polydactyly study was designed to investigate the occurrence of Polydactyly in the B.C. population. Polydactylous infants born in the province in the years 1964 - 1967 were ascertained principally through the Registry for Handicapped Children and Adults; additional cases were found-through disease indexes of B.C. hospitals and through referrals from medical personnel. Data on the probands were obtained by family interviews and review of various medical records. Information compiled for a case included: sex of proband, racial background, parental age, parity of mother, notes on the pregnancy, description of accessory digits, genetic family history, and nature of additional congenital anomalies when rpresent. Incidence of Polydactyly in B.C. for 1964 - 1967 was 1.02 per 1,000 live births. This figure includes patients with multiple congenital anomalies. Of the four years covered by the study, 1966 had the highest incidence (1.35), a year in which a seemingly disproportionate number of ulnar cases occurred. Ninety-five males and 43 females, a sex ratio of approximately 2:1, presented the following types of duplication: radial (31), tibial (6), ulnar (54), fibular (24) and ulnar and fibular (16). It is proposed that cases with both ulnar and fibular accessory digits and cases with ulnar or fibular accessory digits in whose family both ulnar and fibular duplication occur present ulnar-fibular type Polydactyly. Based on cases unassociated with multiple congenital anomalies, specific types of Polydactyly had the following incidences: radial 0.20; tibial, 0.04; polysyndactyly, 0.01; ulnar, 0.32; fibular, 0.16; and ulnar-fibular, 0.09. Genetic histories indicate in 32 families out of 138 there is another individual with Polydactyly. For specific types of Polydactyly the following proportion of cases without multiple congenital anomalies had a positive family history: radial, 5 - 19 %; tibial, 0 %; ulnar, 29 %• fibular, 25 and ulnar-fibular, 73 f°~ Polygenic inheritance of ulnar and of fibular types of Polydactyly is suggested by the finding that the percentage of affected sibs is greater when there is a history of Polydactyly in previous generations (approximately 6.6 %) than for probands with a negative history (1.2 %). The number of affected sibs of the probands (3/107) is in agreement with the number which would be expected for a polygenic trait. Data for ulnar-fibular Polydactyly is more compatible with dominant inheritance with reduced penetrance among females. Fifty percent of the offspring of polydactylous males were affected; a smaller percentage of the children of affected mothers were polydactylous (27.7 %). Nonpenetrance of the Polydactyly gene(s) would seem to be fairly common among females since unaffected mothers are known to pass the trait to their children whereas such an occurrence is unknown for males. . Among ulnar-fibular cases with no history of accessory digits in previous generations, 17.4 % of the sibs were polydactylous. Major congenital anomaly was noted in 33 probands and occurs approximately 3½ times more frequently among the polydactylous infants than the general population. Multiple major anomalies are approximately 25 times more frequent. A polydactylous child found to have one major malformation is twice as likely to have additional major anomalies than a child with one major anomaly who has the normal number of digits. Multiple congenital anomalies were most commonly seen with ulnar-fibular Polydactyly. This may reflect the fact that ulnar-fibular duplication is the type most commonly seen as a feature of various syndromes. In addition to the B.C. findings, literature on Polydactyly has been reviewed. Included are: data on the incidence of Polydactyly in other populations, description of different types of duplication, hypotheses regarding the inheritance of accessory digits, tabulation of the types of Polydactyly seen in various syndromes, and discussion of the morphogenesis of accessory digits in relation to limb embryogenesis.

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