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523 PKU GENE - POSSIBLE CAUSE OF NON-SPECIFIC MENTAL RE-5H TARDATION

The Justification Hypothesis (J. Ped. 81:834, 1972) proposes that deficiencies in non-essential amino acids might cause mental retardation. The mother heterozygous for synthesis of any one of the non-essential amino acids would deprive her fetus partially and the heterozygous or homozygous fetus would be more or less unable to make up for the deficiency. Berman and Ford (Lancet i: 767, 1977) showed that such concatenation of heterozygous mother and heterozygous fetus is associated with significantly lower IQ. Our own work has verified this finding. The possibility that heterozygosity for PKU in mother and fetus might be a cause of a large amount of “non-specific” mental retardation was tested by looking for associated heterozygosity for PKU in mother and child among 12 families in a genetic clinic. Although there is no evidence of PKU in any of these families three showed such association. This is more than 10 times chance and suggests that a major factor in non-specific mental retardation is indeed heterozygosity in mother and fetus, depriving the developing fetus of a normal supply of tyrosine.