Question

Which of the following disorders are caused due to recessive autosomal mutations?

• A. Turner’s syndrome and sickle cell anaemia
• B. Edward’s syndrome and Down’s syndrome
• C. Cystic fibrosis and phenylketonuria
• D. Alzheimer’s disease and Huntington’s chorea

Answer 1

Answer: (C)

Cystic fibrosis is an abnormal recessive disorder of infants, children and young adults that is due to an abnormal recessive autosomal allele present on chromosome 7. In 70% of cases, it is due to deletion of three bases. The disease gets its name from the fibrous cysts that appear in the pancreas. It produces a defective glycoprotein. The defective glycoprotein causes formation of thick mucus in skin, lungs, pancreas, liver and other secretory organs. There is maldigestion of food with high fat content in stool. Liver may undergo cirrhosis. Phenylketonuria is an inborn, autosomal, recessive metabolic disorder in which the homozygous recessive individual lacks the enzyme phenylalanine hydroxylase needed to change phenylalanine to tyrosine in liver. It results in hyperphenylalaninemia which is characterised by accumulation and excretion of phenylalanine, phenylpyruvic acid and related compounds. Lack of the enzyme is due to the abnormal autosomal recessive gene on chromosome 12.