Articles :: Diseases and Gene :: Genetic diseases

Xeroderma Pigmentosum

Xeroderma pigmentosum is a rare autosomal disease caused by the failure of the repair system. XP patients cannot repair dimers induced by UV light. They are 1000 times more easy to catch skin cancer. They catch skin cancer once exposed to sunlight.

They are also more likely to catch other kinds of internal cancers since they cannot repair other errors.

Sickle-cell Anaemia

a sickle cell     Sickle Cell Information Center

People with sickle-cell anaemia have normal-looking erythrocytes when blood oxygen level is high. When the oxygen level falls, the erythrocytes will change from the normal biconcave shape to a sickle, crescent shape. The sickle-cell cannot pass through tiny capillaries, thus blocking them. Other tissue cells are starved from oxygen and food. The patient may feel breathless, tired and may cough.

The consequence of this is fatal. Sickle cells are fragile. They are more liable to break. The number of erythrocytes decreases and the person suffers from anaemia. This is why this disease is called sickle-cell anaemia.

Why do erythrocytes, this faithful and helpful cell become the killer? The problem is in the haemoglobin. Haemoglobin consists of 4 polypeptide chains with a haem for each chain. A pair is named a-polypeptide and the other B-polypeptide. Sickle-cell anaemia is caused by a point mutation. The gene responsible for the coding of the B-polypeptide has a codon GAG converted to GTG. When DNA is copied as RNA, GTG becomes GUG. As a result, valine instead of glutamine is inserted into the polypeptide. When oxygen level is low, the abnormal haemoglobin becomes a long fibre which turns the cell sickle shaped.

Haemoglobin     Sickle Cell Information Center

	Blood of SC patient
	Sickle Cell Information Center

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