Hexosaminidase A (HEX A) deficiency; including some types of Tay-Sachs disease
Inheritance from both parents will result in the disease
Age range at onset:
Specialists you may see:
Classic or infantile onset: symptoms typically first appear between three and five months of age. These may include feeding problems, general weakness (lethargy), and an exaggerated startle reflex in response to sudden loud noises. Motor delays and mental deterioration are progressive.
Late-onset form: symptoms may become apparent anytime from adolescence through the mid-30s. The infantile form often progresses rapidly, resulting in significant mental and physical deterioration. A characteristic symptom of Tay Sachs disease, which occurs in 90 percent of cases, is the development of cherry red spots in the backs of the eyes. Symptoms of late-onset Tay Sachs disease vary widely from case to case. This disorder progresses much more slowly than the infantile form.
Mutations in the HEXA gene reduce its ability to produce an enzyme called beta-hexosaminidase A. This enzyme breaks down GM2 ganglioside. When this is not broken down, it builds up in nerve cells of the brain and spinal cord, causing the described symptoms.