Galactosemia
Classification and external resources
Galactose
ICD-10	E74.2
ICD-9	271.1
eMedicine	ped/818
MeSH	D005693

Galactosemia is a rare genetic metabolic disorder that affects an individual's ability to metabolize the sugar galactose properly. Galactosemia should not be confused nor related to Lactose-Intolerance. Galactosemia follows an autosomal recessive mode of inheritance that confers a deficiency in an enzyme responsible for adequate galactose degradation.

Goppert 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.^[2]

Its incidence is about 1 per 60,000 births (classic type). It is much rarer in Japan and much more common in Italy, specifically the traveler region. Galactosemia is also very common within the Irish Traveller population. This is attributed to consanguinity within a relatively small gene pool.^{[citation needed]}

Contents 1 Cause 2 Types 3 Diagnosis 4 Treatment 5 References 6 External links

[edit] Cause

Lactose

Glucose

Galactose

Lactose in food (such as dairy products) is broken down by the enzyme lactase into glucose and galactose. In individuals with galactosemia, the enzymes needed for further metabolism of galactose are severely diminished or missing entirely, leading to toxic levels of galactose in the blood, resulting in hepatomegaly (an enlarged liver), cirrhosis, renal failure, cataracts, brain damage, and ovarian failure. Without treatment, mortality in infants with galactosemia is about 75%.

[edit] Types

Galactose is converted into glucose by the action of three enzymes, known as the Leloir pathway. Accordingly, there are 3 known types of Galactosemia; type 1, 2 and 3:

Type	Diseases Database	OMIM	Gene	Locus	Enzyme	Name
Type 1	5056	230400	GALT	9p13	galactose-1-phosphate uridyl transferase	classic galactosemia
Type 2	29829	230200	GALK1	17q24	galactokinase	galactokinase deficiency
Type 3	29842	230350	GALE	1p36-p35	UDP galactose epimerase	galactose epimerase deficiency, UDP-Galactose-4-epimerase deficiency

The order of these three types is not the same as the order that the enzymes are encountered by galactose on its metabolic path (which is closer to GALK, GALT, and then GALE, though many variations can occur.)

[edit] Diagnosis

Infants are now routinely screened for galactosemia in the United States, and the diagnosis is made while the person is still an infant. Infants affected by galactosemia typically present with symptoms of lethargy, vomiting, diarrhea, failure to thrive, and jaundice. None of these symptoms are specific to galactosemia, often leading to diagnostic delays. Luckily, most infants are diagnosed on newborn screening. A galactosemia test is a blood test (from the heel of the infant) or urine test that checks for three enzymes that are needed to change galactose-a sugar that is found in milk and milk products-into glucose, a sugar that your body uses for energy. A person with galactosemia doesn't have one of these enzymes. This causes high levels of galactose in the blood or urine.

Galactosemia is normally first detected through newborn screening, or NBS. Affected children can have serious, irreversible effects or even die within days from birth. It is important that newborns be screened for metabolic disorders without delay. Galactosemia can even be detected through NBS before any ingestion of galactose-containing formula or breast milk.

Detection of the disorder through newborn screening (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. A specimen should be taken prior to transfusion. The enzyme is prone to damage if the sample is delayed in the mail or exposed to high temperatures. The routine NBS is accurate for detection of galactosemia. Two screening tests are used to screen infants affected with galactosemia - the Beutler's test and the Hill test. In fact a third test, called the "Florida test", is also normally performed on all galactosemia positives. The Beutler's test screens for galactosemia by detecting the level of enzyme of the infant. Therefore, the ingestion of formula or breast milk does not effect the outcome of this part of the NBS, and the NBS is accurate for detecting galactosemia prior to any ingestion of galactose.

[edit] Treatment

The only treatment for classic galactosemia is eliminating lactose and galactose from the diet. Even with an early diagnosis and a restricted diet, however, some individuals with galactosemia experience long-term complications such as speech difficulties, learning disabilities, neurological impairment (e.g. tremors, etc), and in girls, ovarian failure. These complications are treated if they appear in a manner similar to the way they would be treated in a non-galactosemic. Such complications have not been associated with Duarte galactosemia, and many individuals with Duarte galactosemia do not need to restrict their diet at all. Infants with classic galactosemia cannot be breast-fed due to lactose in human breast milk and are usually fed a soy-based formula.^[3]

Galactosemia is sometimes confused with lactose intolerance, but galactosemia is a more serious condition. 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. In contrast, a galactosemic individual who consumes galactose can cause permanent damage to their bodies.

Long term complication of galactosemia includes:

• Speech deficits
• Ataxia
• Dysmetria
• Diminished bone density
• Premature ovarian failure
• Cataract

[edit] References

[edit] External links

• Galactosemia Resources and Information
• Parents of Galactosemic Children, Inc. website
• What is Galactosemia?
• Galactosemic Families of Minnesota
• Galactosemia Handbook - A Guide for Families
• galactosemia.org
• GeneReview/NIH/UW entry on Galactosemia

v • d • e Inborn error of carbohydrate metabolism: monosaccharide metabolism disorders (including glycogen storage diseases) (E73-74, 271) Sucrose, transport (extracellular) Disaccharide catabolism Lactose intolerance · Sucrose intolerance Monosaccharide transport Glucose-galactose malabsorption · Inborn errors of renal tubular transport (Renal glycosuria) · Fructose malabsorption Hexose → glucose Monosaccharide catabolism fructose: Essential fructosuria · Fructose intolerance galactose/galactosemia : GALK deficiency · GALT deficiency/GALE deficiency Glucose ⇄ glycogen Glycogenesis GSD type 0, glycogen synthase · GSD type IV, Andersen's, branching Glycogenolysis extralysosomal: GSD type V, McArdle, muscle glycogen phosphorylase/GSD type VI, Hers', liver glycogen phosphorylase · GSD type III, Cori's, debranching lysosomal/LSD: GSD type II, Pompe's, glucosidase Glucose ⇄ CAC Glycolysis MODY 2 · GSD type VII, Tarui's, phosphofructokinase · Triosephosphate isomerase deficiency · Pyruvate kinase deficiency Pyruvate catabolism PDHA · Fumarase deficiency Gluconeogenesis PCD · Fructose bisphosphatase deficiency · GSD type I, von Gierke, glucose 6-phosphatase Pentose phosphate pathway Glucose-6-phosphate dehydrogenase deficiency · Pentosuria Other Hyperoxaluria (Primary hyperoxaluria) see also fructose and galactose metabolism enzymes, intermediates; see also glycolysis enzymes, intermediates see also glycogenesis and glycogenolysis enzymes, intermediates; see also pentose phosphate pathway enzymes, intermediates