Question

A karyotype produced from the chromosomes found in a cheek cell could be used to diagnose all of the following genetic disorders except

• A. Turner Syndrome
• B. Trisomy 18
• C. Chromosomal deletion, such as 5p- syndrome
• D. Klinefelter Syndrome
• E. Tay-Sachs Disease

Answer 1

The correct option is E Tay-Sachs Disease

A. Turner syndrome is a genetic disorder that is caused due to abnormality in sex chromosome number. This disorder is produced by the union of an abnormal O egg and a normal X sperm or a normal egg and an abnormal O sperm. The individual has 45 chromosomes (44 + X) instead of 46. Such persons are sterile females who have rudimentary ovaries, undeveloped breasts, short stature, small uterus and abnormal intelligence.

B. Trisomy 18 causes Edward's syndrome, a disorder due to an extra chromosome number 18. Thus the total number of chromosomes is 47. The patient is mentally retarded with long but narrow skull, small face, webbed neck and deafness.

C. 5p- syndrome is caused due to a deletion in the short arm of the chromosome number 5. It is also called Cri-Du-Chat (Cat Cry) syndrome. It is very rare. The patients of this syndrome are affected by microcephaly, increased distance between eyes, moon face, small head.

D. Klinefelter syndrome is a genetic disorder that occurs by the union of an XX egg and a normal Y sperm or normal X egg and abnormal XY sperm. The individual has 47 chromosomes (44 + XXY). Affected males are tall with long legs, some with gynecomastia, small testes, azoospermia, increased urinary excretion of gonadotropins, sparse body hairs.

E. Tay-Sachs disease occurs due to accumulation of a fatty substance, sphingolipid, in nerve cells. The homozygous children show degeneration of central nervous system. This is caused by the enzyme hexosaminidase which in normal individuals exist in two forms A and B. In this disease, only the A form is present and the B form is absent.

Hence, among all the options it's Tay-Sachs disease that does not occur due to abnormality in chromosome number. Instead it is caused due to defect in metabolic functions of the body. So it can't be diagnosed from a karyotype produced from the chromosomes found in a cheek cell.

So, the correct answer is 'Tay-Sachs Disease'.