Galactose-1-phosphate uridylyltransferase galactosemia
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Galactose-1-phosphate uridylyltransferase galactosemia Classification and external resources
Galactose
ICD-10	E74.2
ICD-9	271.1
OMIM	230400
DiseasesDB	5056
eMedicine	ped/818
MeSH	D005693

Galactose-1-phosphate uridylyltransferase galactosemia (or Galactosemia type 1) is the most common type of galactosemia. It is caused by a deficiency in galactose-1-phosphate uridylyltransferase.

Cause

During the preparatory phase of glycolysis, galactose 1-phosphate uridylyltransferase is needed to convert galactose 1-phosphate(G-1-P) to UDP galactose, with UDP-glucose as a UDP donor. If Galactose 1-phosphate uridylyltransferase is absent, galactose and G-1-P would accumulate in blood and tissues as they could not be metabolized. The accumulation of G-1-P is toxic and the biochemical mechanism is still an enigma. There is a strong believe that G-1-P would modulate IMPase function in vivo. G-1-P is suggested as a substrate for IMPase as well as galactose 1-phosphate uridylyltransferase, as the brain depends on IMPase for the supply of free inositol in order to sustain the Phosphatidylinositol bisphosphate signalling, the accumulation would inhibit the production of the second messenger in the signalling system and hence causing a mental retardation.

Symptoms

Galactose 1-phosphate uridylyltransferase galactosemia is characterized by poor growth in children, mental retardation, speech abnormality, vision impairment (due to formation of cataract) and liver enlargement (which may be fatal). Strict removal of galactose from diet is required.

Genetics

Galactose-1-phosphate uridylyltransferase galactosemia has an autosomal recessive pattern of inheritance.

There are two variants of the GALT gene responsible for galactosemia type-1.

• One variant causes so-called classic galactosemia, in which there is an extreme deficiency in galactose-1 phosphate uridyltransferase. The gene for GALT was mapped at 9p13. Most serious conditions are prominent.
• The variant gene, responsible for Duarte galactosemia, leads to about half the normal levels of GALT. Individuals with Duarte galactosemia may experience few or none of the serious symptoms of classic galactosemia.

The severity of the symptoms is dependent on a number of factors, most importantly the amount of lactose in the individual's diet. It is also possible to have one each of the classic and Duarte genes, in which case GALT activity is intermediate.

Reference

Bhat PJ (2003). "Galactose-1-phosphate is a regulator of inositol monophosphatase: a fact or a fiction?". Med. Hypotheses 60 (1): 123–8. PMID 12450779. 

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