Galactose is present in dairy products, fruits, and vegetables. Autosomal recessive Autosomal Recessive Genetic disorders determined by a single gene (Mendelian disorders) are easiest to analyze and the most well understood. If expression of a trait requires only one copy of a gene (one allele)... read more enzyme deficiencies cause 3 clinical syndromes.
See also Approach to the Patient With a Suspected Inherited Disorder of Metabolism Approach to the Patient With a Suspected Inherited Disorder of Metabolism Most inherited disorders of metabolism (inborn errors of metabolism) are rare, and therefore their diagnosis requires a high index of suspicion. Timely diagnosis leads to early treatment and... read more .
Galactose-1-phosphate uridyl transferase deficiency
This deficiency causes classic galactosemia. Incidence is 1/62,000 births; carrier frequency is 1/125. Infants become anorectic and jaundiced within a few days or weeks of consuming breast milk or lactose-containing formula. Vomiting, hepatomegaly, poor growth, lethargy, diarrhea, and septicemia (usually Escherichia coli) develop, as does renal dysfunction (eg, proteinuria, aminoaciduria, Fanconi syndrome), leading to metabolic acidosis Metabolic Acidosis Metabolic acidosis is primary reduction in bicarbonate (HCO3−), typically with compensatory reduction in carbon dioxide partial pressure (Pco2); pH may be markedly low or slightly... read more and edema. Hemolytic anemia Overview of Hemolytic Anemia At the end of their normal life span (about 120 days), red blood cells (RBCs) are removed from the circulation. Hemolysis is defined as premature destruction and hence a shortened RBC life span... read more may also occur.
Without treatment, children remain short and develop cognitive, speech, gait, and balance deficits in adolescence; many also have cataracts, osteomalacia (caused by hypercalciuria), and premature ovarian failure. Patients with the Duarte variant have a much milder phenotype.
Patients develop cataracts from production of galactitol, which osmotically damages lens fibers; idiopathic intracranial hypertension (pseudotumor cerebri) is rare. Incidence is 1/40,000 births.
Uridine diphosphate galactose 4-epimerase deficiency
There are benign and severe phenotypes. Incidence of the benign form is 1/23,000 births in Japan; no incidence data are available for the more severe form. The benign form is restricted to red and white blood cells and causes no clinical abnormalities. The severe form causes a syndrome indistinguishable from classic galactosemia, although sometimes with hearing loss.
Diagnosis of Galactosemia
Diagnosis of galactosemia is suggested clinically and supported by elevated galactose levels and the presence of reducing substances other than glucose (eg, galactose, galactose 1-phosphate) in the urine; it is confirmed by DNA analysis or enzyme analysis of red blood cells, hepatic tissue, or both. All states require routine neonatal screening Screening Tests for Newborns Screening recommendations for newborns vary by clinical context and state requirements. Blood typing is indicated when the mother has type O or Rh-negative blood or when minor blood antigens... read more for galactose-1-phosphate uridyl transferase deficiency. (Also see testing for suspected inherited disorders of metabolism Initial testing Most inherited disorders of metabolism (inborn errors of metabolism) are rare, and therefore their diagnosis requires a high index of suspicion. Timely diagnosis leads to early treatment and... read more .)
Treatment of Galactosemia
Dietary galactose restriction
Treatment of galactosemia is elimination of all sources of galactose in the diet, most notably lactose (a source of galactose), which is present in breast milk, all dairy products, including milk-based infant formulas, and is a sweetener used in many foods. A lactose-free diet prevents acute toxicity and reverses some manifestations (eg, cataracts) but may not prevent neurocognitive deficits. Many patients require supplemental calcium and vitamins. For patients with epimerase deficiency, some galactose intake is critical to ensure a supply of uridine-5′-diphosphate-galactose (UDP-galactose) for various metabolic processes.
The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
Online Mendelian Inheritance in Man® (OMIM®) database: Complete gene, molecular, and chromosomal location information