X-linked infantile spinal muscular atrophy

X-linked infantile spinal muscular atrophy is a severe, rare genetic condition affecting boys, characterized by progressive muscle weakness and respiratory failure.

Overview

X-linked infantile spinal muscular atrophy is a condition that affects only boys. It is characterized by severe muscle weakness, absent reflexes (areflexia), and joint stiffness (arthrogryposis). Due to the severity of the condition, most affected children do not survive past early childhood.

Symptoms

• Muscle and Joint Issues: Severe weakness, joint deformities from birth, and in some cases, broken bones at birth.
• Developmental Regression: Loss of previously acquired motor milestones, such as sitting unassisted.
• Physical Features: Unusually small chin and abnormal curvature of the spine.
• Respiratory Issues: Weakness of chest muscles leads to life-threatening breathing problems.
• Other: Undescended testes (cryptorchidism).

Causes

The condition is caused by mutations in the UBA1 gene. This gene produces an enzyme necessary for protein degradation—the process of breaking down damaged or unneeded proteins. When this process fails, proteins build up inside cells, disrupting normal function and leading to the death of motor neurons, which are essential for muscle movement.

Inheritance

This condition is inherited in an X-linked recessive pattern. Because males have only one X chromosome, a single altered copy of the gene is sufficient to cause the disorder. Females, who have two X chromosomes, would require mutations in both copies to be affected, making the condition significantly more common in males. Fathers cannot pass X-linked traits to their sons.