Which of the following disorders does not show sex-linked inheritance?
1. Haemophilia B
2. Duchenne muscular dystrophy
3. Haemophilia A
4. Tay-Sachs disease

What Is Tay-Sachs Disease?

Tay-Sachs disease is a rare, autosomal recessive genetic disorder caused by a deficiency in the enzyme hexosaminidase A. This enzyme is essential for breaking down a fatty substance called GM2 ganglioside in nerve cells. When this substance accumulates, it leads to progressive damage to the nervous system, especially in infants.

Autosomal Recessive Inheritance Explained

Unlike sex-linked disorders (which are associated with the X or Y chromosomes), autosomal disorders are caused by genes located on non-sex chromosomes (autosomes). Tay-Sachs disease is inherited in an autosomal recessive manner, which means:

• An individual must inherit two defective copies of the HEXA gene (one from each parent) to be affected.

• Carriers (with one defective gene) are typically symptom-free.

Why Tay-Sachs Disease Is Not Sex-Linked

Tay-Sachs is caused by mutations in the HEXA gene located on chromosome 15, which is not a sex chromosome. Therefore:

• Males and females are equally likely to inherit and be affected by the disease.

• It does not follow a sex-linked pattern of inheritance.

Sex-Linked Disorders for Comparison

To clarify, here are examples of sex-linked genetic disorders:

1. Haemophilia A – X-linked recessive disorder caused by deficiency of clotting factor VIII.

2. Haemophilia B – X-linked recessive disorder due to factor IX deficiency.

3. Duchenne Muscular Dystrophy (DMD) – X-linked recessive muscular disorder due to mutations in the dystrophin gene.

In these disorders:

• Males are more commonly affected, since they have only one X chromosome.

• Females can be carriers, often without symptoms.

Diagnosis and Screening for Tay-Sachs

• Genetic Testing: Identifies mutations in the HEXA gene.

• Enzyme Assay: Measures hexosaminidase A activity in blood or tissue.

• Carrier Screening: Recommended for individuals with Ashkenazi Jewish, French-Canadian, or Cajun ancestry, where carrier rates are higher.

Symptoms of Tay-Sachs Disease

• Developmental delay (beginning at ~6 months)

• Loss of motor skills

• Seizures

• Blindness

• Hearing loss

• Death usually occurs in early childhood

Conclusion

While many genetic disorders are sex-linked and more commonly affect males, Tay-Sachs disease stands apart as an autosomal recessive condition. It affects both sexes equally and follows a different inheritance pattern, making it important for genetic counseling and screening in high-risk pop