<prompt> An infant presented to the OPD with a history of vomiting and poor feeding. Musty odor is present in the babys sweat and urine. Guthrie test was done and it was found to be positive. All are true regarding this disease except:Phenylacetate positive in urineTandem mass spectrometry is the gold standard testPhenylalanine hydroxylase enzyme defectmental retardation is absent  <response>: The given clinical condition is suggestive of phenylketonuria PKU PKU is caused by the deficiency of an enzyme phenylalanine hydroxylase. Guthrie bacterial inhibition test is a screening test for phenylketonuria. This test uses a phenylalanine requiring strain of Bacillus subtilis. Ferric chloride test is also used as a screening test for PKU. Tandem mass spectrometry is the gold standard investigation Reference: Harpers illustrated biochemistry 30th edition 