Galactosemia TGAL

The enzymatic reaction of the NEONATAL Total-Galactose Screening Assay is carried out in two stages. In the first stage, two enzymes—alkaline phosphatase and galactose dehydrogenase—convert total galactose (Galactose-1-phosphate and free galactose) in the newborn sample into products, such as NADH. In the second stage, the presence of NADH is quantified using colorimetry with tetrazolium salt. The absorbance intensity measured is directly proportional to the total galactose concentration in the sample.

Galactosemia is defined by an alteration in the metabolism of galactose, caused by a deficient activity of one of the three enzymes involved in its metabolism. Conventional galactosemia, due to complete galactose-1-phosphate uridyl transferase (GALT) deficiency, is the most common and produces the most severe galactosemia symptoms in infants. Two other much rarer forms of galactosemia exist, galactokinase (GALK) and UDP-galactose epimerase (GALE) deficiencies. The genes involved are GALT, GALK1 and GALE, respectively.

Conventional galactosemia is a severe disease that begins when a person swallows milk through eating disorders, lethargy, growth failure, and severe liver and kidney damage. Neonatal sepsis may also occur. A cataract appears within days or weeks. In the longer term, learning difficulties and ovarian failure in girls may occur. Partial deficits, due to a relatively common GALT mutation, called “Duarte”, have a much less severe clinical presentation, which may even remain asymptomatic.

GALK deficiency is responsible for isolated cataracts. GALE deficiency manifests itself as a variable clinical presentation resembling classical galactosemia.

The neonatal screening programs for galactosemia are traditionally based on a total galactose assay and/or GALT activity.

The main objective of long-term treatment of classical galactosemia is to minimize the dietary intake of galactose. This dietary management protects against liver and renal complications, as well as cataracts. However, it does not prevent learning difficulties and hormone disorders from appearing. A follow-up is required and focuses on psychomotor development and gonadal function.