Galactosemia follows an autosomal recessive mode of inheritance that confers a deficiency in an enzyme responsible for adequate galactose degradation.

Friedrich Goppert (1870–1927), a German physician, first described the disease in 1917,[1] with its cause as a defect in galactose metabolism being identified by a group led by Herman Kalckar in 1956.

[7][8] Infants may appear asymptomatic at birth; however, upon ingestion of galactose a few days later (via breast and/or formula feeding), children start to experience life-threatening symptoms, which include:[9] Progression of this acute neonatal toxicity syndrome may include the development of sepsis, cataracts, and even pseudotumor cerebri (which may cause a bulging of fontanelle).

While a child is being treated for galactosemia, they may continue to experience speech delays, learning disabilities, behavioral issues, ataxia, tremors, and hormone deficiencies.

[13] In galactosemic patients, the accumulation of galactose becomes the substrate for enzymes that catalyze the polyol pathway of carbohydrate metabolism.

[citation needed] In many states throughout the world, infants routinely undergo newborn screening (NBS) for galactosemia.

Infants affected by galactosemia typically present with symptoms of lethargy, vomiting, diarrhea, failure to thrive, and jaundice.

Detection of the disorder through NBS does not depend on protein or lactose ingestion, and, therefore, it should be identified on the first specimen unless the infant has been transfused.

[20] Some individuals may experience long-term complications such as speech difficulties, learning disabilities, neurological impairment (e.g. tremors, etc.

However, research corroborates a previously overlooked theory that Duarte galactosemia may lead to language developmental issues in children with no clinical symptoms.

Infants with classic galactosemia cannot be breast-fed due to lactose in human breast milk which consists of both galactose and glucose and are usually fed a soy-based formula.

Lactose intolerant individuals have an acquired or inherited shortage of the enzyme lactase, and experience abdominal pains after ingesting dairy products, but no long-term effects.