Accumulation of this fatty substance causes the distention and eventual destruction of neurons. .
The pattern of inheritance of Tay-Sachs disease is autosomal recessive, in which case the individual should have both recessive alleles to manifest the symptoms of the disease. Moreover, because it is autosomal, the disease does not differentiate between sexes. An individual with Tay-Sachs disease is conceived if both parents are carriers (heterozygous) of the gene. It must be noted that homozygous recessive parents are not possible because individuals with Tay-Sachs disease, as elaborately discussed in the next section, are unable to do motor functions as basic as walking and swallowing. Carrier parents thus have a 25% chance of having a child with Tay-Sachs disease per conception. In addition, they have 50% chance of conceiving carriers, and 25% chance of having a child that does not have a recessive allele. Detection of symptomatic and supposedly homozygous recessive individuals may be determined in prenatal tests or by assaying β-hexosaminidase A activity.
In the case of Rita and Peter, their family medical history presents a strong evidence of autosomal diseases in both families. Rita has a history of one uncle dying at an early age, and Peter had an uncle and an aunt who died at a young age. Although these past cases were undiagnosed, they were all probably Tay-Sachs disease.
There are many forms of this disease, depending on what age the symptoms manifest. The signs and symptoms of the infantile form become initially apparent during infancy, specifically at age 3 to 6 months, wherein there is marked weakening of the muscles and protracted development by the inability to turn over, sit or crawl after an apparently normal development. In addition, they have an increased startle reaction to loud noises, which is one of the primitive reflexes of humans. As the disease progresses, other neural degenerative signs including seizures, intellectual disabilities and paralysis begin to manifest.