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Maharashtra State BoardSSC (Marathi Semi-English) 9th Standard [इयत्ता ९ वी]
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Syllabus

Diseases Occuring Due to Mutation in Single Gene (Monogenic Disorders)

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Topics

  • Introduction
  • Albinism
  • Types of Albinism
  • Sickle-Cell Anaemia
  • Overview of Sickle-Cell Anaemia

Introduction:

Monogenic disorders are diseases caused by a mutation in a single gene. These mutations result in the production of defective or insufficient gene products, disrupting normal body functions. This can lead to abnormal metabolism and, in severe cases, result in early death. Currently, over 4,000 such disorders are identified. These conditions are inherited and can significantly impact an individual’s health and quality of life.

Examples of Monogenic Disorders:

  • Hutchinson’s Disease
  • Tay-Sachs Disease
  • Galactosemia
  • Phenylketonuria
  • Sickle-Cell Anaemia
  • Cystic Fibrosis
  • Albinism
  • Haemophilia
  • Night Blindness

Albinism:

Albinism is a genetic condition characterised by a lack of melanin, the pigment responsible for providing colour to the skin, hair, and eyes. It is caused by mutations in genes that are responsible for melanin production. These mutations lead to either a reduced production of melanin or a complete inability to produce it.

Causes of Albinism:

Albinism occurs due to mutations in genes involved in melanin synthesis. These mutations are inherited in an autosomal recessive pattern, meaning an individual must inherit a defective copy of the gene from both parents to exhibit the condition. The most common gene mutations associated with albinism include:

  • OCA1 (tyrosinase gene mutation): This affects the enzyme responsible for converting tyrosine into melanin.
  • OCA2, OCA3, and OCA4 (other gene mutations): These involve proteins essential for melanin production and transport.

Symptoms and characteristics:

  • Skin: pale or light skin due to little or no melanin. Increased sensitivity to sunlight (photosensitivity), leading to a higher risk of sunburn and skin cancer.
  • Hair: white or very light-coloured hair, which may vary slightly depending on the type of albinism.
  • Eyes: light-coloured or pinkish eyes, as the lack of melanin allows blood vessels in the eye to become visible.

 Hair and eyes of child with albinism

Vision problems such as

  • Photophobia: sensitivity to bright light.
  • Nystagmus: involuntary rapid eye movements.
  • Reduced visual acuity: poor eyesight due to abnormal development of the retina and optical nerves.

Absence of melanin in the retina affects depth perception and causes difficulty focusing on objects. In extreme cases, total blindness can occur if proper care is not taken.

Types of Albinism:

1. Oculocutaneous Albinism (OCA) 2. Ocular Albinism (OA) 3. Hermansky-Pudlak Syndrome

Most common type and affects skin, hair, and eyes.

Primarily affects the eyes. The skin and hair may appear normal.

 A rare type of albinism accompanied by bleeding disorders and lung diseases.

Management and Care:

While there is no cure for albinism, individuals can manage the condition effectively with proper care and precautions-

  • Use broad-spectrum sunscreens with high SPF.
  • Wear protective clothing and hats to avoid direct sun exposure.
  • Wear UV-protected sunglasses or corrective lenses to improve vision and reduce sensitivity to light.
  • Regular eye checkups are essential.
  • Monitor for signs of skin damage or abnormalities to prevent skin cancer.
  • Individuals with albinism often face social stigma and emotional challenges. Counselling and support groups can help them navigate these issues.

Sickle-Cell Anaemia:

Sickle-cell anaemia is a hereditary disorder caused by a mutation in the gene responsible for the production of haemoglobin, the protein in red blood cells (RBCs) that carries oxygen. This mutation alters the structure of haemoglobin and affects the shape and function of RBCs.

Sickle cells

Causes of Sickle-Cell Anaemia:

In normal haemoglobin, the 6th amino acid is glutamic acid. In sickle-cell haemoglobin, this is replaced by valine due to a genetic mutation. This change causes haemoglobin molecules to stick together under low oxygen conditions, resulting in abnormally sickle-shaped RBCs instead of the normal biconcave shape.

Effects on the Body:

  • Sickle-shaped RBCs cannot carry oxygen efficiently, leading to oxygen deprivation in tissues and organs.
  • Sickle-shaped cells tend to clump together, causing blockages in blood vessels. This leads to damage in vital organs like the brain, lungs, kidneys, and circulatory system.
  • Sickle cells break down more quickly than normal RBCs, resulting in anaemia (low RBC count).
  • Symptoms include fatigue, weakness, and shortness of breath.

Sickle-cell anaemia is inherited from parents. If both parents are carriers or affected, their offspring have a high likelihood of inheriting the disease. Carriers (individuals with one defective gene and one normal gene) do not typically show symptoms but can pass the gene to their children.

Overview of Sickle-Cell Anaemia

There are two types of persons affected by sickle-cell anaemia

  1. Sickle-cell anaemia carrier (AS)
  2. Sufferer from sickle-cell anaemia (SS)

Symptoms of sickle-cell anaemia:

  • Swelling of hands and legs
  • Pain in joints
  • Severe general body aches
  • Frequent colds and coughs
  • Constant low-grade fever
  • Exhaustion
  • Pale face
  • Low haemoglobin content

Sickle cell anaemia occurs as follows :
Symbols: AA = Normal, AS = Carrier, SS = Sufferer

Sr. No. Man Woman Progeny
1 AA AA Normal progeny if both parents are normal.
2 AA or AS AS or AA 50% progeny normal and 50% carrier, if one parent is normal and one is a carrier.
3 AA or SS SS or AS All progeny will be carriers if one parent is normal and one is a sufferer.
4 AS AS 25% progeny normal, 25% sufferer, and 50% carrier if both parents are carriers.
5 AS or SS SS or AS 50% progeny carrier and 50% sufferer if one parent is a carrier and one is a sufferer.
6 SS SS All progeny will be sufferers if both parents are sufferers.

Diagnosis of sickle-cell anaemia:

Under the National Health Mission scheme, the ‘Solubility Test’ for diagnosis of sickle-cell anaemia is available at all district hospitals. Similarly, the confirmatory diagnostic test ‘Electrophoresis’ is performed at rural and sub-district hospitals.

Hand of a child with sickle-cell anaemia

Precautions and Management:

This disease is spread in only one way, i.e., reproduction. Hence, husband and wife should get their blood examined either before marriage or after it.

  1. A carrier or sufferer should avoid marriage with another carrier or sufferer.
  2. A person suffering from sickle-cell anaemia should take a tablet of folic acid daily.
  3. Regular monitoring and early treatment can help manage symptoms.
  4. Treatments like pain relievers, blood transfusions, and medications to boost red blood cell production are used.
  5. Avoiding physical stress and maintaining hydration can prevent complications.
  6. Individuals should seek immediate medical care during episodes of severe pain or illness.
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