Which of the following porphyrias is not inherited as an Autosomal Dominant disorder -

Porphyrins are normal pigment present in haemoglobin, myoglobin and cytochrome. Porphyria refers to an uncommon disorder of inborn abnormality of porphyrin metabolism. It results from a genetic deficiency of one of the enzymes required for the synthesis of haem, resulting in excessive production of porphyrins. Often, the genetic deficiency is precipitated by the intake of some drugs. Porphyrias are associated with excretion of intermediate products in the urine--delta-aminolaevulinic acid, porphobilinogen, uroporphyrin, coproporphyrin, and protoporphyrin. Porphyrias are broadly of 2 types--erythropoietic and hepatic. (a) Erythropoietic porphyrias: These have a defective synthesis of haem in the red cell precursors in the bone marrow. These may be fuher of 2 subtypes: Congenital erythropoietic porphyria, in which the urine is red due to the presence of uroporphyrin and coproporphyrin. The skin of these infants is highly photosensitive. Bones and skin show red-brown discolouration. Erythropoietic protoporphyria, in which there is an excess of protoporphyrin but no excess of porphyrin in the urine. (b) Hepatic porphyrias. These are more common and have a normal erythroid precursor but have a defect in the synthesis of haem in the liver. Its fuher subtypes include the following: Acute intermittent porphyria is characterised by acute episodes of 3 patterns: abdominal, neurological, and psychotic. These patients do not have photosensitivity. There is excessive delta-aminolaevulinic acid and porphobilinogen in the urine. Porphyria cutanea tarda is the most common of all porphyrias. Porphyrins collect in the liver and a small quantity is excreted in the urine. Skin lesions are similar to those of invariegate porphyria. Most of the patients have associated haemosiderosis with cirrhosis which may eventually develop into hepatocellular carcinoma. Mixed (Variegate) porphyrias. It is rare and combines skin photosensitivity with acute abdominal and neurological manifestations. Ref: TEXTBOOK OF PATHOLOGY 6th EDITION - HARSH MOHAN PAGE NO:42-43