DISCUSSION

Two siblings were referred for workup for progres-sive neurological deterioration. The elder sibling was a 16- year-old boy who had been asymptomatic until 9 years of age when he developed walking difficulty that progressed to a bed-bound state followed by regression of cognitive function and generalized tonic clonic seizures. The younger sibling was a 14-year-old girl with onset of similar symptoms at the age of 6 years. The siblings were the eldest of 6 chil-dren from a family with no history of consanguinity. Both children principally ate a high-carbohydrate (maize)-based diet with sporadic access to fresh pro-duce and animal protein. They had reached normal developmental milestones until the onset of symp-toms. Both children had been treated unsuccessfully with sodium valproate. On examination, they dem-onstrated minimal communication skills and severe cognitive impairment. They had spastic paralysis of all extremities. Electroencephalography in the elder sibling re-vealed generalized, highly potentially epileptogenic foci, and a brain computed tomography scan dem-onstrated marked cerebral atrophy with minimal white matter. Initial laboratory investigations, in-cluding a complete blood count, measurement of electrolytes and urea, and thyroid and liver function tests, were all within reference intervals. Syphilis se-rology was negative. Screening for inherited meta-bolic diseases included measurements of plasma amino acids and urine organic acids. Selected laboratory results of the elder boy are provided i