R. Rodney Howell

Neurotransmitter defects and treatment of disorders of hyperphenylalaninemia

The disordered biosynthesis of dopamine, norepinephrine, and serotonin in brain in untreated PKU is corrected by dietary restriction of phenylalanine. Low levels of biogenic amine metabolites were measured in cerebrospinal fluid from three patients with classical PKU; metabolite concentrations increased after dietary treatment. In a variant of hyperphenylalaninemia caused by deficiency of dihydropteridine reductase, there is defective metabolism of biogenic amines despite dietary restriction of phenylalanine. Two siblings with DHPR deficiency had low amine metabolite values in CSF; in one patient the metabolic defect was corrected by administration of hydroxylated amino acid precursors. Defective biosynthesis of biogenic amines in brain in disorders associated with hyperphenylalaninemia and evaluation of specific dietary treatments can be determined by analysis of neurotransmitter metabolites in CSF.

Genetic evidence for the common identity of glucose-6-phosphatase, pyrophosphate-glucose phosphotransferase, carbamyl phosphate-glucose phosphotransferase and inorganic pyrophosphatase.

We demonstrate that glucose-6-phosphatase, pyrophosphate-glucose phosphotransferase, carbamyl phosphate-glucose phosphotransferase and inorganic pyrophosphatase activities are deficient in livers of patients with type I glycogen storage disease. This provides strong genetic evidence that these enzymatic activities reside in a single protein or share a common polypeptide chain.

Development of gluconeogenic enzymes in fetal sheep liver and kidney.

In the sheep, the system of enzymes necessary for conversion of nonhexose substrates to glucose becomes active during late fetal life. Glucose-6-phosphatase and fructose-1,6-diphosphatase, two of the four key gluconeogenic enzymes, appear in significant amounts between 100 and 120 days gestation. Phosphoenolpyruvate carboxykinase activity is comparable to mature animals as early as 45 days gestation. Two aminotransferases, necessary to allow amino acid access to the gluconeogenic pathway, likewise have substantial activity as early as 45 days gestation. Hence, the surge of glucose-6-phosphatase and fructose-1,6-diphosphatase at 100-120 days gestation makes possible the endogenous production of new glucose by fetal sheep at a time when the amount of glucose transferred from the maternal circulation is less than the total aerobic substrate utilized by the fetus. Both renal cortex and liver have similar developmental patterns for the gluconeogenic enzymes, although renal cortex generally shows greater activity than liver. This observation holds true for tissue from both fetal and mature animals.