Galactosemia consists of four types of disorders resulting from abnormal activity of the enzymes involved in galactose metabolism. Type I/ Classical is the most serious form of the disease.

Galactosemia refers to a group of autosomal recessive disorders of galactose metabolism. They are classified into the following types based on the enzymatic activity ^[1]

• Defects in both copies of the gene that codes for the enzyme galactose-1-phosphate uridyl transferase or GALT.^[2].
• Most common and severe form.
  • Duarte galactosemia
    • Variant of classic galactosemia.
    • Galactose metabolised to some extent as GALT not completely absent
    • Less severe symptoms than other forms

• Defect in both copies of the gene that codes for the enzyme galactokinase or GALK.^[3]
• Less common and harmful than classic galactosemia.
• Does not generally lead to hepatomegaly or brain damage.

• Alterations in the gene coding for epimerase enzyme.^[4] This is the mildest type.

• This type has only been discovered recently.
• Abnormal changes in the galactose mutatrose enzyme, encoded by the GALM gene, have been proven to cause the disorder. ^[5]