Phenylketonuria (PKU) is the most frequent inherited metabolic disorder and results in progressive mental retardation. The incidence of PKU varies widely in neonates: it is high in Turkey (1:2600) and Ireland (1:4500) and low in Japan (1:125 000).1

The incidence of the disease is unknown in Tunisia and North Africa. In the absence of a newborn screening program for PKU and considering the high rate of consanguineous marriages in Tunisia, this study aimed to assess the incidence of PKU among institutionalised patients with a mental handicap.

A total of 833 patients from 17 different centres for the mentally handicapped in Tunisia were included. Patients with a known genetic syndrome (eg, Down syndrome) were excluded. The included patients were 6–46 years of age, and the sex ratio was 2.19 male(s)/females. Blood spots were collecting using Guthrie cards and phenylalanine was analysed using the fluorimetric method. The patient was considered to have PKU when the level of phenylalanine was higher than 4 mg/100 ml.1

Eleven (1.32%) of 805 included patients were diagnosed as having PKU. These patients were divided into two groups according to the French classification2: eight patients (0.96% of the total sample) had the classical form of PKU and three patients (0.36% of the total sample) had the moderate form of PKU. Patients were fairly evenly distributed across the country with three from the north, three from the middle and five from the south of Tunisia.

This frequency of 1.32% is close to the frequency of 1.6% observed in the two largest Kuwaiti institutions for the mentally handicapped and to the frequency of 1.9% reported in 1934 by Asbjörn Fölling in Norwegian institutions for the mentally handicapped before neonatal screening for PKU was routinely carried out.1 3 In an Iranian study, approximately 2.2% of 1541 patients in eight different institutions for the mentally handicapped in the province of Isfahan had PKU.4 In contrast, biochemical screening for inherited metabolic disease in mentally handicapped patients in the Alexandra institute in Cape Town revealed only three patients with PKU, giving a frequency of 0.2% which is considerably lower than those reported in similar studies elsewhere.5

The screening data clearly indicate the relatively high frequency of the disease among patients in Tunisian centres for the mentally handicapped, and highlight the need for neonatal screening in the Tunisian population in light of the high incidence of PKU.