Which one of the following is not the symptoms of phenylketonuria?

The correct answer is Option (4) → Furrowed tongue and partially open mouth

Phenylketonuria (PKU) is an inborn error of metabolism. It is inherited as an autosomal recessive trait. The affected person lacks the enzyme that changes the amino acid phenylalanine into tyrosine. So phenylalanine builds up, and it is converted into phenylpyruvic acid and other derivatives. When these collect in the brain, they cause mental retardation. The kidney absorbs them poorly, so they are also passed out in the urine.

(1) Accumulation of phenylalanine — A symptom of phenylketonuria. The missing enzyme leaves phenylalanine unused.

(2) Phenylpyruvic acid excretion through urine — A symptom of phenylketonuria. The extra phenylalanine is changed into this acid, which passes out in the urine.

(3) Mental retardation — A symptom of phenylketonuria. It is caused by the build-up of these products in the brain.

(4) Furrowed tongue and partially open mouth — Not a symptom of phenylketonuria. These are features of Down’s syndrome, which is caused by trisomy of chromosome 21.

NCERT Extract:
Mendelian Disorders – “… Phenylketonuria : This inborn error of metabolism is also inherited as the autosomal recessive trait. The affected individual lacks an enzyme that converts the amino acid phenylalanine into tyrosine. As a result of this phenylalanine is accumulated and converted into phenylpyruvic acid and other derivatives. Accumulation of these in brain results in mental retardation. These are also excreted through urine because of its poor absorption by kidney.”
Chromosomal Disorders – “… Down’s Syndrome : The cause of this genetic disorder is the presence of an additional copy of the chromosome number 21 (trisomy of 21). This disorder was first described by Langdon Down (1866). The affected individual is short statured with small round head, furrowed tongue and partially open mouth (Figure 4.16).”