A term born 6-month-old, lethargic blonde infant, presented with multiple episodes of vomiting, poor feeding, convulsions and severe psychomotor retardation. O/E: - Microcephaly with prominent maxillae and widely spaced teeth Blue iris Seborrheic or eczematoid rash Spasticity, hyperreflexia, and tremor Musty odour of urine MRI brain All of the following statements are true about the disease except: -