Y. Edward Hsia

Heritable urea cycle enzyme deficiency-liver disease in 16 patients.

The liver mitochondrial enzymes ornithine transcarbamylase and carbamyl phosphate synthetase I catalyze the first two steps in the Krebs-Henseleit pathway from ammonia to of either of these enzymes has been associated with severe and sometimes fatal hyperammonemia in infancy and childhood, but liver histology has usually been described as normal. The Reye syndrome also causes severe hyperammonemia and produces characteristic light microscopic changes in the liver. In addition, OTC and CPS activities have been shown to be depressed and it has been suggested that some cases of the Reye syndrome may reflect an inborn defect in OTC which predisposes the patient to the Reye syndrome. Review of the histopathology of 15 liver specimens from 13 patients with OTC deficiency and three liver specimens from three patients with CPS deficiency has disclosed the following: (1) hemizygous male infants with X-linked OTC deficiency had essentially normal liver histology, although fatally affected with extreme hyperammonemia; (2) in contrast, almost all heterozygous female children and adults had some histologic abnormalities, including nine with minor degrees of steatosis and eight with focal cell necrosis and inflammation, two of whom had piecemeal necrosis and stellate portal scarring; (3) livers from heterozygotes had discrete clusters of larger, pale-staining hepatocytes; (4) female heterozygotes had abnormal liver function, even after the hyperammonemia was controlled; (5) CPS deficient patients had essentially normal liver histology; and (6) neither OTC nor CPS deficiency was associated with a histologic picture which resembled that seen in the Reye syndrome.

Human Propionyl CoA Carboxylase: Some Properties of the Partially Purified Enzyme in Fibroblasts from Controls and Patients with Propionic Acidemia

Summary: We report some properties of propionyl CoA carboxylase (PCC) partially purified from cultured human fibroblasts obtained from controls and several patients with propionic acidemia. A series of steps (Triton X-100 treatment, high speed centrifugation, ammonium sulfate precipitation, and density gradient centrifugation) led to 100− to 300− fold purification of control enzyme. Control PCC had a molecular weight of nearly 700,000, contained biotin, demonstrated a pH optimum at 8.0–8.5, was activated by potassium, and followed Michaelis-Menten kinetics for each of its substrates. It was distinguished from acetyl CoA carboxylase immunologically as well as by differential purification.Each of seven lines from patients with propionic acidemia had clearly detectable PCC activity which was less than 5% of that in control lines. Although yields were poor and purification less extensive than in control lines, mutant PCC was enriched 2− to 40-fold by the same procedures employed for the control enzyme. Mutant enzyme had a pH optimum, ionic requirements, and substrate Kms similar to those of control PCC, but was distinctly more labile to both cold and heat. These findings suggest that the markedly reduced activity of PCC in these patients results from a mutation in the PCC structural gene locus or loci which leads to the synthesis of altered enzyme protein molecules.Speculation: Our results suggest that human propionyl CoA carboxylase has properties very similar to those of other mammalian propionyl CoA carboxylases. Further chemical studies with control enzyme and that from patients with propionic acidemia may help define the basis for the two major genetic complementation groups reported among propionyl CoA carboxylase deficient patients.

Propionic acidemia: Diagnosis by enzyme assay in frozen leukocytes

Summary A simplified and miniaturized assay is described for propionyl-CoA carboxylase activity. Leukocytes have measurable amounts of this enzyme, which is markedly reduced in patients with propionic acidemia. The stability of this enzyme permits shipment of whole blood or frozen leukocyte pellets for diagnostic assay. It has been possible to establish or refute the diagnosis of propionic acidemia in specimens of blood transported from other medical centers.

Genetic counseling for congenital heart disease

The genetic knowledge of parents of children with congenital heart disease, who had received genetic counseling, was compared with that of a control noncounseled group attending the same cardiac clinic. A follow-up questionnaire showed that both groups had excellent knowledge of the nature of their childrens heart lesions. The counseled group had significantly more accurate knowledge of their recurrence risks. Inasmuch as the reproductive attitudes of some of these parents were found to be influenced by genetic information, parents of children with CHD should be given a better understanding of recurrence risks for CHD than many of them possess.

Hepatolenticular degeneration: The comparative effectiveness of D-penicillamine, potassium sulfide, and diethyldithiocarbamate as decoppering agents

Copper balance studies were performed on three patients with hepatolenticular degeneration to assess the relative values of D-penicillamine, of potassium sulfide, and of diethyldithiocarbamate therapy. The first produced a pronounced negative balance, whereas the latter two were essentially ineffective.

A Study of Inheritance in Progressive Intrahepatic Cholestasis: Hepatic excretory Function in Unaffected Family Members

Summary: In an attempt to identify the heterozygotes state for progressive intrahepatic cholestasis (PIC), hepatic excretory function (131I rose bengal half-life (t½) and bromosulpthalein-transport maximum (BSP-Tm) was studied in controls and in eight members of a family, two of whom are affected with PIC. Values for 131I rose bengal t½ varied over a wide range in normal controls and were normal in patients with the syndrome of cholestasis and peripheral pulmonic stenosis in whom BSP-Tm and 45 min % retention were abnormal. 131I rose bengal t½ was abnormal in seven of eight family members. Despite this, BSP studies, including Tm, percent retention at 45 min, clearance were normal in all unaffected family members with the exception of the mother who has a reduced BSP-Tm. Fasting serum bile acid studies were normal in all unaffected family members. These studies do not clearly define the inheritance in this syndrome and suggest that any of the following three possibilities exist: 1) that the methods employed were not sensitive enough to detect heterozygotes, 2) that the inheritance in this syndrome is heterogenous; for instance, compound heterozygotes or autosomal dominant, or 3) that the family studies here represents a syndrome different from PIC.Speculation: It has been suggested that the mode of inheritance of progressive intrahepatic cholestasis is autosomal recessive. The use of sensitive tests of hepatic excretory function (such as the t½ 131I rose bengal and the BSP-Tm may identify heterozygotes and confirm the type of inheritance.

Propionyl-CoA carboxylase deficiency (propionicacidemia): A cause of non-ketotic hyperglycinemia

Propionyl-CoA carboxylase deficiency is now thought to be the primary enzyme defect in the disease previously called “ketotic hyperglycinemia”. In a 10 month old girl with mental retardation and seizures, who never showed clinical attacks of ketoacidosis while eating a usual infant diet, we found hyperglyinuria, modest hyperglycinemia (2.4–2.9 mg%; normal 1.6 ± 0.3 mg%), and an impaired plasma clearance of glycine after an oral load. Studies of glycine catabolism by leukocytes in vitro were normal but a sever defect in propionate oxidation was present. In addition, propionyl-CoA carboxylase activity in extracts of cultured fibroblasts was less than 1% of normal. To investigate propionate metabolism in vivo, oral amino acid loads were given. Isoleucine, a propionyl-CoA precursor, led to vomiting, lethargy, ketonuria, hyperlactatemia, and hyperammonemia within 1 day. Valine, which is metabolized to methylmalonyl-CoA, the product of the deficient enzyme, caused hyperammonemia within 1 day. VAline, which is metabolized to methylmalonyl-CoA, the product of the deficient enzyme, caused hyperammonemia but no symptoms, no ketonuria, and no increase in lactate over a five day period. Plasma glycine remained between 3.1 and 5.1 mg% during the oral isoleucine and valine loads. Thus, propionyl-CoA carboxylase deficiency need not cause clinical attacks of ketoacidosis and must be considered in any infant with even slightly evelvated plasma and urine glycine concentrations.