MOLECULAR-BASIS OF PHENYLKETONURIA AND A CORRELATION BETWEEN GENOTYPEAND PHENOTYPE IN A HETEROGENEOUS SOUTHEASTERN US POPULATION

Objective. To determine the molecular basis of phenylketonuria (PKU) a nd related hyperphenylalaninemia (HPA) and to establish correlations b etween phenylalanine hydroxylase (PAH) genotypes and biochemical and c linical phenotypes in an ethnically diverse US population, PAH genotyp es were determined in 35 patients with PKU or HPA and 1 carrier from t he Medical Genetics Clinic of the Emory University School of Medicine. Methodology. Patients were identified through Georgia's population-ba sed newborn screening program. PAH genotypes in these individuals were determined from dried blood spots or whole-blood samples using a comb ination of polymerase chain reaction-mediated amplification, denaturin g gradient gel electrophoresis, and direct-sequence analysis. The phen otypic severity of patients with PKU and HPA was based on pretreatment serum phenylalanine (PHE) levels during the neonatal period and on di etary tolerance of PHE later in life. Results. Sixty-eight (96%) of 71 mutant alleles were identified. Major mutations in this population in cluded R408W (11 of 71), I65T (11 of 71), Y414C (6 of 71), L348V (4 of 71), and IVS10 ( 1 of 71). Five new nucleotide substitutions, E76A (1 of 71), R241L (1 of 71), Q304R (2 of 71), C334S (1 of 71), and R400R (2 of 71) were also detected. Thirty-two of the thirty-five nonrelated patients examined in this study were completely genotyped. Strong cor relations were observed between the level of PAH activity predicted fr om the genotype, when known from previous in vitro expression studies of the mutant proteins, and pretreatment serum PHE levels (r = .841) o r clinical severity (Kendall rank-order correlation coefficient, .936) . Conclusions. These results demonstrate strong correlations between P AH gene type and biochemical and clinical phenotypes in this heterogen eous American sample population, extending our previous findings from relatively homogeneous European populations. These correlations furthe r demonstrate the clinical utility of genotype analysis in the treatme nt of patients with PKU and HPA.