Final answer:
The patient's symptoms of areflexia, hepatosplenomegaly, cherry red macula, and milestone regression are indicative of Tay-Sachs disease, a genetic disorder caused by a malfunction of the lysosomal enzyme, leading to a buildup of fatty substances in the brain(option b).
Step-by-step explanation:
The question refers to a 2-6 month old patient displaying areflexia, hepatosplenomegaly, cherry red macula, and milestone regression. The correct diagnosis among the options given is Tay-Sachs disease (b).
Tay-Sachs disease is a genetically inherited autosomal recessive disorder that causes a dangerous buildup of lipids in the nerve cells of the brain. This is due to a malfunctioning lysosomal enzyme, hexosaminidase A, that normally breaks down fatty substances. This malfunction leads to a progressive deterioration of nerve cells, which can manifest with symptoms mentioned in the question, including exaggerated startle response and the characteristic cherry red spot on the macula.
Other disorders listed, such as Niemann-Pick disease, Gaucher disease, and Krabbe disease, also involve storage issues of substances within cells but have a different presentation or set of symptoms. While they might also present with hepatosplenomegaly, the specific combination of signs and symptoms provided in the question is most indicative of Tay-Sachs disease.