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Biochemistry

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Carbohydrates

Question
60 out of 78
 

Galactosemia commonly is due to deficiency of:



A Galactose- 1-phosphate uridyltransferase

B Galactose- 1 -Phosphatase

C Glucose- 1-Phosphatase

D Glucose-6-phosphatase

Ans. A Galactose-1-phosphate-uridyl transferase

a. Galactosemia may be caused by inherited deficiency (defects) in Galactokinase, Galactose- 1- phosphate Uridyl transferase or uridine-Diphosphogalactose 4-Epimerase, though a deficiency in

Galactose-1 -phosphate uridyl transferase is the Best known.

b. In this, polyol (galactitol) which accumulates causing cataract

GALACTOSEMIA:

a. Classic galactosemia is due to deficiency of galactose — 1-phosphate uridyl transferase (GALT) and

is typically associated with cataract formation, mental retardation and cirrhosis.

- 2nd one is due to galactokinase deficiency, leads primarily to cataract formation.

- 3rd one is due to UDP-galactose-4-epimerase deficiency — rarest type

b. In galactokinase deficiency galactose accumulate in the blood and tissues in the lens, galactose is

converted into galactitol by Aldose reductase ed galactitol in lens Hydration cataract.

c. Both galactokinase and GALT deficiencies are transmitted as AR trait. GALT is a polymorphic enzyme and the

most common variant, called the DUARTE VARIANT has reduced activity. The M.C. mutation of the GALT gene

that causes classic galactosemia is the 0188R substitution (G).

d. C/F of classic galactosemia - of gal-1-PO4in kid, liver and brain damage the organs]

i. Symptoms begin with in days to weeks after birth; the infant usually is resistant to ingest breast

ii. milk or, milk formulas, develops vomiting, shows poor nutrition and, fails to thrive.

iii. Jaundice, hepatomegaly, and evidence of liver disease may develop.

iv. Cataracts are usually not present at birth but develops gradually over weeks to months

v. MR becomes evident after 6 to 12 months and usually not reversible.

vi. Infants are subject to bacterial sepsis (especially Escherichia coli) and this may be the leading cause

of death.

e. Cirrhosis and MR are related to increased amounts of galactose- 1-phosphate in these tissues

f. Note that, the only consistent feature of galactokinase deficiency is cataract formation.

5. Treatment -

a. Removal of galactose from diet, especially milk

b. Milk substitutes such as Nutramigen are often used

c. galactose —free diet usually leads to a dramatic improvement in all C/F except for MR.

d. Pt should be kept on galactose free diet indefinitely or at least until they have attained adequate physical and neurological development.

[Note that ed Hb A1ab level in blood of galactosemic pt due to non-enzymatic glycosylation

of Hb. In DM, there is ed 4Hb A1c]

Carbohydrates Flashcard List

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