Pahhph-5: a mouse mutant deficient in phenylalanine hydroxylase.

Abstract

Mutant mice exhibiting heritable hyperphenylalaninemia have been isolated after ethylnitrosourea mutagenesis of the germ line. We describe one mutant pedigree in which phenylalanine hydroxylase activity is severely deficient in homozygotes and reduced in heterozygotes while other biochemical components of phenylalanine catabolism are normal. In homozygotes, injection of phenylalanine causes severe hyperphenylalaninemia and urinary excretion of phenylketones but not hypertyrosinemia. Severe chronic hyperphenylalaninemia can be produced when mutant homozygotes are given phenylalanine in their drinking water. Genetic mapping has localized the mutation to murine chromosome 10 at-or near the Pah locus, the structural gene for phenylalanine hydroxylase. This mutant provides a useful genetic animal model affected in the same enzyme as in human phenylketonuria.Disorders ofphenylalanine catabolism, resulting in phenylketonuria (PKU) and hyperphenylalaninemia (HPH), were among the first heritable errors of metabolism discovered in the human (1). The rate-limiting step in mammalian phenylalanine catabolism is hydroxylation to produce tyrosine. This reaction, catalyzed by phenylalanine hydroxylase (PAH) (2), requires the reduced pteridine cofactor tetrahydrobiopterin (3), which is synthesized from GTP (4) through a number of intermediates and is maintained in its reduced form by quinonoid dihydropteridine reductase (q-DHPR) (5). Mutations reducing the activity of PAH, q-DHPR, or the enzymes involved in tetrahydrobiopterin synthesis result in HPH because of a block in phenylalanine hydroxylation (6). In humans, PKU is defined as a condition resulting from mutations that abolish or severely reduce PAH activity (7). Other defects in phenylalanine catabolism are termed HPH. Extensive research has been undertaken to characterize these disorders (early work is reviewed in refs. 8 and 9 with recent summations in refs. 10 and 11). Laboratory mice with defined PKU and HPH mutations would be helpful in evaluating features of these diseases by permitting investigations not acceptable with human subjects. To produce such mutants we have used the alkylating agent N-ethyl-N-nitrosourea, which induces mutations in the mouse germ line at a frequency near 10-3 per locus (12). We refer to all mutants with deficiencies in phenylalanine catabolism by their common phenotype, HPH. We have screened the progeny of 347 gametes and have isolated four mutant pedigrees exhibiting the HPH phenotype. One of these, HPH-1, was detected by its neonatal HPH phenotype and is deficient in GTP cyclohydrolase activity (13)(14)(15). The others were detected by their impaired ability to clear a phenylalanine challenge (described in ref. 13). One of these, HPH-5, we now report to be deficient in PAH. MATERIALS AND METHODSBiochemical Determinations. Liver homogenates were prepared for PAH assay as described in ref. 16 methyltetrahydropterin, and the enzyme extract. The background rates of NADH oxidation were determined in the absence ofphenylalanine and ind...

An animal model of early-treated PKU

“…Shortly after birth (P4), the pups chosen from the remaining a-methylphenylalanine + Phe litters (group 1) weighed roughly 20% less than pups chosen from the other litters [mean weights = 8.3 f 0.8 gm (group l), 10.0 f 1.3 gm (group 2), 10.2 + 1.6 gm (controls); F(1,32) = 17.05, p < 0.0003, regression analysis of P4 weights in group 1 vs the other two groups]. This difference in infant mortality and weight is similar to that reported by others (e.g., Kerr et al, 1968;Brass et al, 1982;McDonald et al, 1990), and occurred despite the yoking of food intake. By P 12 the difference in weight among the groups of rat pups had disappeared.…”

PAHdb 2003: What a locus-specific knowledgebase can do

“…Three mouse Pah mutations have been artificially created: Pah enu1 [McDonald et al, 1990]; Pah enu2 ; and Pah enu3 [Shedlovsky et al, 1993]. The Pah enu3 allele is now historic.…”

Pathologic and Immunohistochemical Findings in Hypothalamic and Mesencephalic Regions in the Pahenu2 Mouse Model for Phenylketonuria

“…The Pah enu2 mouse is a suitable model to study PKU as it exhibits similar clinical characteristics as human patients that include hyperphenylalanemia, hypopigmentation (5,6), and cognitive defects. Cabib et al (7) found these mice to have cognitive deficits that involve spatial and nonspatial recognition that is separate from motor impairment and not related to emotional reactivity to novel situations.…”