Classic Galactosemia is a rare genetic metabolic disorder. The child with classic galactosemia inherits a gene for galactosemia from both parents, who are carriers. Patients who inherit the classic galactosemia gene from each parent are sometimes described as having the genetic makeup "G/G". Normally when a person consumes a product that contains lactose (e.g., dairy products such as milk, cheese, butter), the body breaks the lactose down into galactose and glucose. Glucose is the sugar used by the body for energy. Galactosemia means too much galactose in the blood caused by the individual "missing" the enzyme (known as GALT) to convert galactose into glucose. This accumulation of galactose is a poison to the body and can cause serious complications such as the following and if untreated, as high as 75% of infants will die:

an enlarged liver
kidney failure
cataract
brain damage

Diagnosis is made usually within the first week of life by blood test from a heel prick as part of a standard newborn screening. Treatment requires the strict exclusion of lactose/galactose from the diet. Although galactosemic children are started on diet restriction at birth, there continues to be a high incidence of long-term complications involving speech and language, fine and gross motor skill delays and specific learning disabilities. Ovarian failure may occur in girls. Prenatal diagnosis by amniocentresis is also available.