Pruritis (Itching) is caused by deficiency of -
Ans. is 'd' i.e., Uroporphyrinogen - III synthase Porphyriaso Porphyrias are heterogenous group of disorders characterized by defective metabolism of porphyrins. Porphyrins are important intermediates in biosynthesis of heme from glycine and succinyl CoA. Each step is controlled by specific enzyme. So, prophyrias are due to inherited or acquired deficiency of enzymes in heme bio-synthetic pathways (also called porphyrin pathway). They manifest with either neurological complications or skin problems (or rarely both). Based on the site of overproduction and accumulation of porphyrins, porphyrias are broadly classified as:-A) Acute (hepatic prophyria)i) Acute intermettant porphyriaii) 5-ALA dehydratase deficiencyiii) Hereditary Coproporphyriaiv) Variegate porphyriav) Porphyria cutanea tardaB) Cutaneous (erythropoeitic) porphyriai) Erythropeitic protoporphyriaii) Congenital erythropoeitic porphyriaiii) X-linked sideroblastic Anemiao The acute (hepatic) porphyrias primarily affect nervous system resulting in abdominal pain, vomiting, acute neuropathy, seizures, muscle weakenss, psychiatric/mental symptoms (i.e., Hallucination, depression, anxiety, paronoia); and autonomic nervous disturbances like hypertension, tachycardia, constipation, arrhythmias, sweatingo The cutaneous (erythropoietic) porphyrias primarily affect skin causing photosensitivity (photodermatitis) blisters, itching, maculopapular rash. There is no abdominal paino There are some variation in above presentation.1) Following two types of hepatic (acute) porphyrias also affect skin: - Hereditary coproporphyria and varigatedporphyria. Therefore these two have both neuropsychiatric as well as skin manifestations.2) Porphyria cutanea tarda (a hepatic porphyria) does not have neuropsychiatric symptom, rather it has only skin manifestation.3) X-linked sideroblastic anemia (an erythropoietic porphyria) has neither neuropsychiatric nor skin symptoms.TypeEnzyme involvedAcute intermittent PorphyriaUroporphyrinogen-I synthase, (also called PBG deaminase or HMB synthase)Congenital erythropoieticUroporphyrinogen III SynthasePorphyria cutanea tardaUroporphyrinogen decarboxylaseHereditary coproporphyriaCoproporphyrinogen oxidaseVariegate porphyriaProtoporphyrinogen oxidaseProtoporphyriaFerrochelatase (Heme synthase).
HMB synthase
5-ALA dehydratase
Uroporphyrinogen - I synthase
Uroporphyrinogen - III synthase
Metabolism of Purines and Pyrimidines