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

A. Acute Intermittent Porphyria (AIP)
B. Hepatic Porphyria
C. Erythropoietic Porphyria (EPP)
D. Porphyria Cutanea Tarda (PCT)

**Core Concept:** Porphyrias are a group of rare disorders characterized by the buildup of porphyrins, a type of organic molecule, in the body. They are classified into two main types: Hemolytic Porphyrias and Atypical Porphyrias. Porphyrias are inherited in various modes, including Autosomal Dominant (AIP, EPP), Autosomal Recessive (Hepatic Porphyria, Erythropoietic Porphyria, Porphyria Cutanea Tarda), Mitochondrial (Acute Intermittent Porphyria), and X-Linked (Porphyria Cutanea Tarda).

**Why the Correct Answer is Right:** Porphyria Cutanea Tarda (PCT) is not inherited as an Autosomal Dominant disorder. Instead, it is inherited as an X-linked disorder in males or arises due to alcohol consumption and/or exposure to certain drugs or hepatitis C virus in females. PCT is characterized by skin lesions, liver disease, and increased susceptibility to infection.

**Why Each Wrong Option is Incorrect:**

A. Acute Intermittent Porphyria (AIP) is an Autosomal Dominant disorder caused by a deficiency in the enzyme delta-aminolevulinic acid synthase. It affects the nervous system, causing severe neurological symptoms and can lead to life-threatening complications if not diagnosed and treated promptly.

B. Hepatic Porphyria is an Autosomal Dominant disorder caused by a deficiency in the enzyme delta-aminolevulinic acid dehydratase. It affects the liver, leading to liver dysfunction and hepatic manifestations.

C. Erythropoietic Porphyria is an Autosomal Recessive disorder caused by a deficiency in the enzyme delta-aminolevulinic acid dehydratase. It affects erythropoiesis, leading to anemia and bone marrow dysfunction.

D. Porphyria Cutanea Tarda (PCT) is an X-linked disorder caused by a deficiency in the enzyme delta-aminolevulinic acid synthase. It is characterized by skin lesions, liver disease, and increased susceptibility to infection.

**Core Concept:** Autosomal Dominant disorders are inherited in such a way that the affected gene is present on autosomes, and a person must inherit only one mutated gene to develop the condition. In contrast, X-linked disorders are inherited from a parent with the mutated gene on the X chromosome. A person must inherit two mutated genes to develop the condition.

**Clinical Pearls:**

- Identifying the type of porphyria (e.g., Autosomal Dominant or X-linked) can aid in determining inheritance patterns and