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Although the clinical heterogeneity of phenylketonuria (PKU) is well established, some questions about this condition remain. Subjects from the same family who share the same mutations in the phenylalanine hydroxylase ( PAH ) gene are expected to display similar disease courses, and therefore, when blood phenylalanine (Phe) levels, genotype and dietary treatment are all similar, differences in patient outcomes require additional explanations. The present authors describe two entirely different courses of late-detected PKU in two brothers with the same R  W/R  X genotype in the PAH gene. The older sibling was diagnosed with PKU at the age of  years and given treatment. His IQ was  at  years of age and moderate involvement of periventricular white matter was detected. The younger brother was diagnosed with PKU at the age of  months and given treatment. His IQ was <  at  years of age and severe dysmyelination changes were found by magnetic resonance imaging. The differences in the courses of the disease between these two brothers appear to be related to variations in their blood-brain barriers.

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(J Med Screen 2001;8:132-136)

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The linked alpha-amylase loci Amy 1 and Amy 2 were evaluated for their linkage relationship to the PKU locus using data collected from two (one Czech and one Polish) groups of families. The five sibships informative for Amy 1:PKU give a z score of 1.505 at theta = 0.00 and the eight sibships informative for Amy 2:PKU give a z score of 2.709 at theta = 0.00. Due to the tandem position of Amy 1 and Amy 2 loci, these data could be combined, and linkage between Amy and PKU loci established with a z score 4,214 at theta = 0.00. The practical significance of the linkage, especially for identifying PKU allele carriers, is emphasized.

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