Frequency of phenylketonuria in Norway

By January 1973, a total of 146 homozygotes (born between 1875 and 1972) for phenylketonuria (PKU) had been identified in Norway. This is an incomplete total, particularly in respect of PKU cases born before 1950, because of the PKU mortality rate. Between 1951 and 1972, the observed incidence of PKU was unchanged at 0.07 plus and minus 0.01 per 1000 live births. Haematological screening of about one-third of all births in Norway between 1966 and 1972 indicated an incidence of 0.07 plus and minus 0.02 per 1000 liveborn screened. As expected, this was well below the observed incidence of 0.11 plus and minus 0.01 per 1000 from screening data from Denmark, and considerably higher than the observed value of 0.03 plus and minus 0.01 per 1000 screened in Sweden. In comparison, indirect estimates, using the inbreeding coefficent of parents of PKUs and that of the general population in Norway in the corresponding years (1874-1972), suggested a fall in incidence of PKU in Norway from 0.14 plus and minus 0.15 per 1000 live births in 1918, to 0.08 plus and minus 0.08 per 1000 in 1941, and to 0.06 plus and minus 0.06 per 1000 live births in 1972. The present level of inbreeding in Norway (obtained from the Medical Registration of Bith) is discussed and compared with information in the 1891 census, with the parish registers between 1889and 1902, and with the parochial lists for the years 1903-1941.