Free online Biochemistry lectures especially for medical students by Biochemistry Club
Deficiency of Niacin
Deficiency of Niacin leads to a disease called Pellagra meaning “rough skin”.
- Niacin is synthesized from tryptophan. Quinolinate phosphoribosyl transferase is the rate limiting enzyme.
- Apart from the deficiency of Niacin, Pellagra can also be caused by the deficiency of Tryptophan.
- Pellagra is seen more in women; this may be because tryptophan metabolism is inhibited by estrogen metabolites.
- The symptoms of pellagra are:
- In early stages, bright red erythema occurs, especially in the feet, ankles and face.
- Increased pigmentation around the neck is known as Casal’s necklace.
- The dermatitis is precipitated by exposure to sunlight
- The diarrhea may be mild or severe with blood and mucus.
- This may lead to weight loss.
- Nausea and vomiting may also be present.
- It is frequently seen in chronic cases.
- Delerium is common in acute pellagra.
- Irritability, inability to concentrate and poor memory are more common in mild cases.
- Ataxia, and spasticity are also seen.
Causes of Niacin Deficiency
1. Dietary deficiency of tryptophan
- Pellagra is seen among people whose staple diet is maize (South and Central America).
- In maize, niacin is present; but it is in a bound form, and is unavailable.
- Pellagra is also seen when staple diet is sorghum (jowar or guinea corn) as in Central and Western India.
- Sorghum, contains leucine in high quantities.
- Leucine inhibits the QPRT enzyme …
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