Tay-Sachs Disease

History and Physical Findings

John Doe and Kristal Doe, a young and healthy, non-consanguineous couple, were expecting their first child. Genetic testing was not recommended, as they had no knowledge of heritable disease in their family histories. The fetus developed normally and a healthy baby girl named Mary Doe was born. She developed normally for the first six months at which point she had learned to roll over and lift her head, but her mother noticed that she was startled easily. Mary Doe subsequently started missing developmental milestones. Around the age of one, Mary’s parents started noticing a developmental decline characterized by spastic movements of the limbs, stiff and flexed limbs, inability to lift her head and roll over, labored breathing, difficulty eating, and decreased interest in her surroundings. ohn Doe and Kristal Doe took Mary to the pediatrician who noticed a red spot in her eye and ordered genetic testing, which confirmed the diagnosis of Tay-Sachs disease. The family was told that there is no cure for this progressive genetic disorder, and in the months that followed, they could only keep Ashley comfortable as her symptoms slowly worsened with regular seizures, inability to move, and inability to eat, until her death just shy of her second birthday1.

Background

Disease Etiology

Tay-Sachs disease (TSD) is a fatal autosomal recessive condition caused by a β-hexosaminidase A (HEXA) enzyme deficiency. HEXA deficiency is associated with greater than 100 mutations affecting gene HEXA, which is located on chromosome 152,3. The associated mutations are varied, including: duplications, insertions, small deletions, single base substitutions, etc.3. This disorder is neurodegenerative and can man...

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...es all of these different mutations together is that they involve the HEXA gene on Chromosome 15. This gene is responsible for the HEXA enzyme that is necessary for the breakdown of GM2 gangliosidoses. Without this functional HEXA enzyme, lysosomal storage problems, like TSD, arise and lead to degeneration.

5. How does Tay-Sachs disease demonstrate the genetic principle of variable expressivity?

Tay-Sachs disease can be classified into three different categories depending on the period of life in which the symptoms manifest. Each category is similar in that they are all progressive neurodegenerative disorders. The younger the individual is when the symptoms begin however, the more severe the symptoms and the disease progresses quicker. This could be due to the point of central nervous system development in which the degeneration of neurons starts to occur.