Prevalence of classical phenylketonuria in mentally retarded individuals in Iran.

Using Guthrie Biological Inhibition Assay, 4963 mentally retarded individuals housed in 31 cities and towns across the country were screened for PKU. The average prevalence of classical PKU in the study population was 2.1%, which is higher than that reported for most mentally retarded populations in other countries prior to the implementation of a nationwide newborn screening programme for PKU. The prevalence of PKU in 1814 mentally retarded inmates housed in shelters in Tehran was 2.81%, and the prevalence of the disease in 3149 inmates sheltered in other cities and towns was 1.68%. It appears that most of the difference between the prevalence of PKU in these two populations is due to a unique PKU referral pattern in Iran. The high prevalence of PKU in the mentally retarded population in Iran could be indicative of a high incidence of the disease among Iranian neonates. This in turn appears to be positively influenced by both a high frequency of the PKU allele and a high rate of consanguinity in the country. Our finding suggests that instead of limited local screening programmes in the country, a nationwide screening programme for PKU, especially if coupled with screening for congenital hypothyroidism, would be highly cost-effective and warranted.