Model Answer
0 min readIntroduction
Haemophilia is a rare, inherited bleeding disorder in which the blood doesn't clot normally. This deficiency arises due to a lack or malfunction of clotting factors, proteins essential for blood coagulation. Historically recognized as a ‘royal disease’ due to its prevalence in European royal families, haemophilia impacts individuals’ ability to form stable blood clots, leading to prolonged bleeding even from minor injuries. Understanding the genetic basis of this condition is crucial for diagnosis, genetic counseling, and potential therapeutic interventions. This answer will detail the causes, symptoms, and genetic inheritance patterns of haemophilia.
Understanding Haemophilia: Causes and Types
Haemophilia is primarily caused by mutations in genes that provide instructions for making the clotting factors needed to form blood clots. There are several types of haemophilia, categorized by the specific clotting factor that is deficient or malfunctioning:
- Haemophilia A: The most common type (approximately 80-85% of cases), caused by a deficiency in clotting factor VIII.
- Haemophilia B: Also known as Christmas disease, caused by a deficiency in clotting factor IX.
- Haemophilia C: A milder form, caused by a deficiency in clotting factor XI.
These mutations can be spontaneous (de novo) or inherited from a parent. The severity of haemophilia depends on the level of the deficient clotting factor in the blood.
Symptoms of Haemophilia
The symptoms of haemophilia vary depending on the severity of the factor deficiency. Common symptoms include:
- Prolonged bleeding: This can occur after injuries, surgery, or dental work.
- Easy bruising: Individuals with haemophilia bruise easily, often with large, deep bruises.
- Joint pain and swelling: Bleeding into joints can cause pain, swelling, and long-term damage. This is particularly common in severe haemophilia.
- Blood in urine or stool: Indicates internal bleeding.
- Nosebleeds: Frequent and difficult-to-stop nosebleeds.
- Prolonged bleeding from cuts or wounds: Even minor cuts can bleed for a long time.
- Internal bleeding: Can occur spontaneously, without any apparent injury.
In severe cases, spontaneous bleeding into muscles and organs can occur, posing a life-threatening risk.
Genetic Inheritance of Haemophilia
Haemophilia A and B are X-linked recessive disorders. This means the gene responsible for the condition is located on the X chromosome. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
Here's how inheritance works:
- Females: A female must inherit two copies of the mutated gene (one on each X chromosome) to have haemophilia. If she inherits only one copy, she is a carrier – she doesn't have the condition herself but can pass the mutated gene on to her children.
- Males: A male only needs to inherit one copy of the mutated gene on his X chromosome to have haemophilia, as he has no second X chromosome to compensate.
Haemophilia C is autosomal recessive, meaning it is not sex-linked and affects males and females equally. Both parents must carry the mutated gene for a child to inherit the condition.
Punnett Square Illustration (Haemophilia A/B)
Consider a carrier female (XHXh) and a normal male (XHY), where XH represents the normal allele and Xh represents the haemophilia allele:
| XH | Y | |
|---|---|---|
| XH | XHXH (Normal Female) | XHY (Normal Male) |
| Xh | XHXh (Carrier Female) | XhY (Haemophilic Male) |
As shown, there is a 50% chance of a normal male, 50% chance of a carrier female, 25% chance of a normal female and 25% chance of a haemophilic male.
Conclusion
Haemophilia, a debilitating inherited bleeding disorder, arises from deficiencies in crucial clotting factors. Its symptoms range from easy bruising to life-threatening internal bleeding. The X-linked recessive inheritance pattern of Haemophilia A and B significantly impacts the likelihood of transmission, with males being more frequently affected. Advances in genetic testing and factor replacement therapies have dramatically improved the quality of life for individuals with haemophilia, but continued research is vital for developing curative treatments like gene therapy.
Answer Length
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