Amino Acids, Proteins and Porphyrins
Arthritis occur in:
|C||Maple syrup diseases|
a. Alkaptonuria: Defective catabolism of tyrosine due to deficiency of Homogentisic oxidase. C/f →
i. Urine darkening (blackening) on exposure to air due to oxidation
ii. Ochronosis (generalized pigmentation of connective tissue): due to deposition of Benzoquinone acetate
iii. Arthritis — Mainly involves large joints but spare small joints.
b. Cystinosis: - (cystine storage disease): - Rare lysosomal disorder Characterized by defective carrier mediated transport of cystine, cystine crystals are deposited in RES, and pts die due to acute episodes.
c. Please do not confuse with cystinuria→ Defective renal absorptive mechanism for 4-amino acid —
Cysteine, Lysine, Arginine and Ornithine (= COLA) their excretion ↑ed is urine.
d. Homocystinuria: Defective catabolism of methionine up to 300 mg Homocystine with S-Adenosylmethionine is excreted in urine per day. Type 1-homocystinuria is due to deficiency of cystathionineβ-synthase, and C/F →thrombosis, osteoporosis, lens dislocation and mental retardation
*Both vitamin B6 responsive and vit. B6 — unresponsive forms are known.
e. Maple syrup urine disease →Defective metabolism of branched chain α-keto amino acid (Leucine,
Isoleucine and valine = LIV), due to deficiency or reduced activity of α-keto acid decarboxylase: Maple
syrup or Burnt sugar odour of urine.