Galactosemia refers to a group of genetic metabolic disorders that have a disturbed galactose metabolism. This results in three different clinical pictures:
I : The classic galactosemia (life-threatening): the infants have feeding problems, a slowed growth, lethargy, diarrhea, hypoglycemia, poor weight gain and jaundice. The metabolite galactose-1-phosphate accumulates in the brain, kidneys, liver and erythrocytes, where it causes toxic damage.
II : Galactokinase deficiency (rarer, milder form): primarily with cataract, other symptoms of galactosemia are absent. Already in the first step of the conversion of galactose into glucose is disturbed, which is why galactose accumulates in the blood and is excreted in the urine. Due to the oversupply of galactose, it is converted in the eye lens to its alcohol galactitol, where it leads to the formation of cataracts.
III : Galactose-epimerase deficiency (very rare with varying degrees of severity): symptoms vary according to severity, with the most common symptoms being feeding problems, jaundice, hypotonia, vomiting and weight loss. In addition, there is often a disrupted growth, cognitive deficits and cataracts.
The cause of the different galactosemias are mutations in the genes GALT (9p13), GALK1 (17q24) and GALE (1p36). All three genes encode essential enzymes for galactose metabolism. Inheritance is autosomal recessive in all cases.
The disease manifests itself usually already in the neonatal period or in childhood. The severe mental disorders and mental retardation come from the deposition of galactose-1-phosphate in the brain. Affected girls suffer from hypogonadism with ovarian dysfunction.