The lack of galactose-1-phosphate uridine nucleotide conversion enzyme in the patient’s body does not allow the intermediate production of galactose 1-phosphate galactose to be transformed into glucose 1-phosphate, which causes the accumulation of galactose and galactose 1-phosphate in the body and affects the organism, especially the damage to the brain is predominant. The infant was born normal and developed symptoms only after being breastfed or cow’s milk fed. The severity and time of appearance of symptoms are related to the amount and duration of galactose ingested. Clinical manifestations are drowsiness, vomiting, diarrhea, aggression, edema, hepatomegaly, jaundice, skin and mucosal hemorrhage, cataracts and hypoglycemic convulsions. Intellectual development is delayed. Due to renal involvement, protein, tubular and galactose may be present in the urine. Galactose (CH2OH(CHOH)4CHO) is a type of monosaccharide that can be found in milk products or sugar beets. Galactose is a monosaccharide consisting of six carbons and an aldehyde, classified as an aldose and a hexose. Galactose is a component of lactose in the milk of mammals and polysaccharides composed of D-galactose have been found from snails, frog eggs and bovine lungs. It is often found in brain and nerve tissue as D-galactoside and is also an important component of certain glycoproteins. Galactose is often found in the plant kingdom as a polysaccharide in a variety of plant gums, for example, K-carrageenan in red algae is a polysaccharide composed of D-galactose and 3,6-endoether-D-galactose. Free galactose is found in the berries of ivy. Galactose is a white crystal. both D-galactose and L-galactose occur naturally. d-galactose is generally found in milk as a structural part of lactose, which is broken down by the body into glucose and galactose for absorption and utilization. Because it contains calories, it is also used as a nutritional sweetener. Galactose is part of the lactose molecule and the other half is glucose. Galactose can be obtained from the hydrolysis of lactose, catalyzed by beta-lactase. Bifidobacterium bifidum ferments lactose to produce galactose, which is a component of cerebroside lipids that make up the brain nervous system and is closely related to the rapid growth of the brain after birth. A few weeks after birth, liver disease including cholestasis, extensive steatosis, non-inflammatory cell infiltration, later pseudobiliary duct formation, pseudoglandular hyperplasia, hepatocyte destruction, and pseudoglandular hyperplasia are characteristic of galactosemia, but not specific. Fine fibrous tissue hyperplasia appears with disease progression. Fibrous tissue hyperplasia begins in the periportal area and later extends toward the portal area to form bridging connections and later forms regenerative nodules. The changes during cirrhosis are similar to those of alcoholic cirrhosis, and there is always no significant inflammatory cell infiltration throughout the course of the lesion. In addition to liver lesions, renal tubular dilatation at the renal cortical and medullary junctions, splenomegaly may result from portal hypertension, and mild brain lesions. The severity of disease varies widely, with some children presenting with acute, fulminant disease after the first breastfeeding, while more often presenting with a subacute course. Gastrointestinal symptoms, including jaundice, loss of appetite, abdominal distention, diarrhea, vomiting, and hypoglycemia. Ascites appears at about 2 to 5 weeks, cataracts can appear within a few days after birth, and if the mother eats too much milk during pregnancy, the infant can be born with jaundice. Under normal conditions, after breastfeeding, the lactose contained in milk is broken down by digestive enzymes into galactose and glucose, and galactose is formed into galactose-1-phosphate by the action of kinase, which is then converted in the liver by galactose-1-phosthate uridyltransrerase Gal-1-PUT. Glucose-1-phosphate, which enters the enzymatic pathway. If Gal-1-PUT loses its function due to structural changes caused by genetic mutations, galactose metabolism is blocked and galactose accumulates in the blood and tissues and is excreted in the urine. The intermediate product galactose-1-phosphate (Gal-1-P ) is harmful to cells and mainly invades the liver, kidneys, brain and lens, so the affected child develops vomiting, diarrhea and dehydration a few days after breastfeeding. After a week, the liver is enlarged and jaundice, ascites and cataracts appear. A few months later, intellectual developmental disorders appear and often die prematurely. This is galactosemia. If not fed milk and dairy products after birth, the infant can develop completely normally. Treatment involves removing all sources of galactose from the diet, most importantly lactose, which is found in all dairy products and in many food sweeteners. Although a galactose-removal diet often prevents acute toxicity, long-term complications (such as poor growth, speech and neurological abnormalities, and mental retardation) are still common. Many patients require calcium and vitamin supplements. If dairy foods are stopped midway through the course of the disease, symptoms may improve, but intelligence does not return. What is the difference between galactosemia and lactose intolerance? 1. Lactose intolerance: There is lactase in the human intestine, which breaks down lactose into glucose and galactose for absorption. Generally speaking, the lactase activity in the intestines of newborn infants is very high, and after 2 to 5 years of age, the enzyme activity gradually decreases and drops to very low in adulthood. Adults of European ethnicity have high lactase activity. Lactase deficiency in the adult intestine is called lactase deficiency, while in infants it is called lactose intolerance. Patients are unable to digest and absorb lactose from milk and exhibit varying degrees of diarrhea. If lactose is removed from the food the symptoms can disappear. 2. Galactosemia: The large amount of galactose produced after digestion and absorption of lactose needs to be enzymatically converted into glucose derivatives in the human body before it can be further metabolized and utilized. Very few infants are born without the relevant enzymes, resulting in a large accumulation of galactose derivatives that cannot be converted into glucose in the body, which is called galactosemia, showing symptoms such as growth arrest and mental retardation. Infants with galactosemia can grow to adulthood normally if they are fed a de-lactose diet.