Abstract
A Japanese family, in which three members (propositus and his two sibs) are of phenotype P2k, and the frequency of Pk in Japanese population are described.
The family (Fig. 1). The propositus (II-6) is a 38-year-old healthy donor who comes from Iwate Prefecture in the northern part of Japan. His parents (I-1 and I-2) are first cousins. Two (II-5 and II-9) of five sibs of the propositus were also P2k and the other members of the family were P2. Anti-P in the serum from the three P2k members was mainly IgG and partly IgM, though they had no history of blood transfusion.
The P2k members were tested for the 20 immunogenetic and biochemical systems (Table 1) and it was found that a gene responsible for Pk is independent of the loci for ABO, MNSs, Rh, Kidd, Hp, Gc, ACP, PGM1 and GPT.
Frequency of Pk. The frepuency of the phenotype Pk was studied by two different ways.
1) During the last ten years, we have found three examples of Pk for the accompanying anti-P in testing over 270, 000 Japanese donors and pregnant women and their husbands, a frequency of 0.00001 (0.001%) with a upper limit (95% certainty) of 0.00002 (0.002%).
2) A total of 7 Pk propositi, including one reported in this paper, have so far been found in Japan (Hayashida, 1968; Yamaguchi et al., 1974; Furukawa et al., 1974; Furukawa and Kishi, 1976; Nakajima and Yokota, 1977). Four of the 7 propositi are the offspring of first cousin marriage: rate of the first cousin marriages is 57% and it raises to 71% if second cousins are included. According to Imaizumi et al. (1975), the mean rate of first cousin marriages in Japan until 1957 is about 5% (inbreeding coefficient=0.004).
By putting these values into the Dahlberg's formula, the frequency of gene responsible for Pk was estimated at 0.0026-0.0013 and that of phenotype Pk at 0.00017-0.000007 or 1 in 60 to 140 thousand. These figures are almost in agreement with those estimated in the population studies mentioned above. The rate of first cousin marriages in Japan has, however, shown a rapid decrease in recent two decades, showing about 1% or less (Imaizumi et al., 1975). Thus, the frequency of phenotype Pk in young people might be much lower than the above-estimated values.
