Type VI: Liver phosphorylase Liver Mild hypoglycemia with Usually none Probably good Hers hepatomegaly, ketonuria
Type VII: Muscle Muscle Clinical findings similar to None Similar to that of type V Tarui phosphofructokinase
Type VIII Phosphorylase kinase Liver Clinical findings similar to type None Good III, without myopathy
GI, Gastrointestinal. *Except for one form of hepatic phosphorylase kinase, which is X-linked, these disorders are autosomal recessive.
Figure 52-1 Glycogen synthesis and degradation. (1) Glycogen synthetase, (2) brancher enzyme, (3) debrancher enzyme, (4) phosphoglucomutase, (5) glucose-6-phosphatase.
blood glucose levels or supplying alternative energy sourcesto muscle. In glucose-6-phosphatase deficiency (type I), thetreatment usually requires nocturnal intragastric feedings ofglucose during the first 1 or 2 years of life. Thereafter, snacksor nocturnal intragastric feedings of uncooked cornstarchmay be satisfactory; hepatic tumors (sometimes malignant)are a threat in adolescence and adult life. No specific treatment exists for the diseases of muscle that impair skeletalmuscle ischemic exercise. Enzyme replacement early in lifeis effective in Pompe disease (type II), which involves cardiacand skeletal muscle.
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Galactosemia is an autosomal recessive disease caused by deficiency of galactose-1-phosphate uridyltransferase (Fig. 52-2).Clinical manifestations are most striking in a neonate who, when fed milk, generally exhibits evidence of liver failure (hyperbilirubinemia, disorders of coagulation, hypoglycemia), disordered renal tubular function (acidosis, glycosuria, aminoaciduria), and cataracts. The neonatal screening test must have a rapid turnaround time because affected infants may die in the first week of life. Affected infants are at increased risk for severe neonatal Escherichia coli sepsis. Major effects on liver and kidney function and the development of cataracts are limited to the first few years of life; older children may have learning disorders despite dietary compliance. Girls usually develop premature ovarian failure despite treatment.
Laboratory manifestations of galactosemia depend on dietary galactose intake. When galactose is ingested (as lactose), levels of plasma galactose and erythrocyte galactose
Figure 52-2 Pathway of galactose metabolism. (1) Lactase (intestinal), (2) galactokinase, (3) galactose-1-phosphate uridyltransferase, (4) uridine diphosphoglucose 4-epimerase.
1-phosphate are elevated. Hypoglycemia is frequent, and albuminuria is present. Galactose frequently is present in the urine and can be detected by a positive reaction for reducing substances without a reaction with glucose oxidase on urine strip tests. The absence of urinary reducing substances cannot be relied on to exclude the diagnosis. The diagnosis is made by showing extreme reduction in erythrocyte galactose-1-phosphate uridyltransferase activity. DNA testing for the mutations in galactose-1-phosphate uridyltransferase confirms the diagnosis and may be useful in predicting prognosis. Renal tubular dysfunction may be evidenced by a normal–anion-gap hyperchloremic metabolic acidosis. Treatment by the elimination of dietary galactose results in rapid correction of abnormalities, but infants who are extremely ill before treatment may die before therapy is effective.