Galactosemia. An autosomal recessive disorder of galactose metabolism that is caused by deficiencies in one of 3 enzymes involved in the metabolism of galactose: galactose-1-phosphate uridyltransferase (GALT), galactokinase (GALK), and uridine diphosphate galactose-4-epimerase (GALE).
Classic galactosemia is the most common and most severe and is caused by deficiency of the galactose-1-phosphate uridyltransferase (GALT) enzyme. It affects ∼1 in 10,000 to 1 in 30,000 live births. Deficiency of the GALT enzyme results in accumulation of galactose-1-phosphate and other metabolites that are thought to be toxic to the liver and other organ systems. The gold standard of diagnosis is measurement of GALT activity in the erythrocytes. Clinical presentation is variable and nonspecific in the neonatal period (occurs after ingestion of galactose-containing formula) and includes vomiting, loose stools, prolonged jaundice, irritability, and poor weight gain. Continued ingestion of galactose results in multiorgan toxicity with hepatomegaly, worsening liver dysfunction, splenomegaly, renal dysfunction, and CNS involvement. These infants, while on lactose-containing formula, have galactose in the urine, resulting in a positive reducing substance in the urine (Clinitest reagent tablets) but negative urine dipstick test for glucose (glucose oxidase). A cataract may be detected on examination. “Oil-drop” cataracts are highly typical of galactosemia and may resolve with treatment if diagnosed early. Neonatal sepsis due to Escherichia coli and other gram-negative organisms is more frequent in galactosemic infants. The reason for this unique predisposition remains unclear. Treatment for galactosemia consists of immediate removal of galactose in the diet as soon as diagnosis is suspected. Liver disease usually improves, but long-term neurodevelopmental complications may develop later despite good dietary control.
Galactokinase deficiency (GALK) results in accumulation of galactose, galactitol, and galactonate and leads to early onset of juvenile bilateral cataract. Although uncommon, pseudotumor cerebri, mental retardation, hepatosplenomegaly, hypoglycemia, and seizures have been described in GALK-deficient patients.
The rarest and most poorly understood among the 3 types is epimerase deficiency (GALE). Natural history of epimerase-deficiency galactosemia is limited due to the small number of patients reported to date. When a diet containing lactose is not removed immediately, infants typically present with generalized hypotonia, poor feeding, vomiting, weight loss, progressive cholestatic jaundice, hepatomegaly, liver dysfunction, aminoaciduria, and cataracts. Prompt removal of galactose from their diet resolves or prevents acute symptoms.
α1-Antitrypsin deficiency. The most common inherited cause of neonatal hepatitis syndrome, with an incidence of 1 in 1600 to 1 in 2000 live births in North American and European populations, α1-antitrypsin is the most abundant proteinase inhibitor, and it acts by inhibiting destructive proteases. Clinical diagnosis is made by documenting low serum concentration of α1-antitrypsin and identifying the phenotypic variant based on differences in isoelectric point (Pi), with M being normal and Z being most deficient. There are several phenotypes; however, the homozygous Pi (protease inhibitor) ZZ is the most likely associated with neonatal liver disease and adult emphysema. Despite carrying the same mutation, only 10–15% of newborns present clinically. Treatment is mostly supportive or liver transplantation if cirrhosis is progressive. Outcome is related to severity of neonatal liver disease; 50% of children are clinically normal by 10 years of age, 5–10% require liver transplantation, and in 20–30% of patients, cholestasis resolves with residual evidence of cirrhosis that may eventually require liver transplantation.