Question

A late acting dominant disease is
A. Tay-Sachs disease
B. Polydactyly
C. Huntington's chorea
D. Phenylketonuria

Answer 1

Hint: A dominant disease is the one that can be expressed in the heterozygous form. Only one allele is enough for the expression of the disease. While a recessive disease requires both the alleles in order to express the disease. A late acting disease is a progressive disease that does not present itself as soon as acquired but starts with the symptoms slowly and then the symptoms get severe.

Complete answer:
Tay-Sachs disease is a rare inherited disorder. It is featured by the destruction of nerve cords in the spine and the brain.
Polydactyly is the presence of more than five fingers or toes. These are present from birth.
Phenylketonuria is also a disease that is an inherited defect in the phenylalanine amino acid.
Huntington’s disease is a neuronal disorder involving the brain. It is a progressive disease. The defect is present in a gene on chromosome four. This defect leads to degenerative changes in the nerves of the brain.
The disease is dominant. A single gene from a single parent is enough to cause the disease in the progeny. The progeny gets the disease even if the defect is present in only one parent. The symptoms of this disease are usually present between the age gap of 30 and 50 years. Thus, the disease is late onset and progresses over years and takes a long time to reach the presenting state.
Thus Huntington's chorea is a late acting dominant disease.
The correct answer is Option C.

Note:
The symptoms that a Huntington's patient presents are with a psychiatrist mostly. It leads to loss of cognitive abilities. Juvenile Huntington’s is the one that develops at the age of 20 years. Juvenile Huntington’s progresses faster than the adult onset Huntington’s.