Fourth Case : Another Toddler in a Different World

One morning you woke up to discover that the world had changed and somehow you had become a peads consultant . you were still pondering over the implications of this new life in your office when a 24-month-old boy presented to you with no speech, unsteadiness when standing, and a history of seizures since 12 months of age. He was the product of a normal pregnancy, labor, and delivery. He had no speech or syllables, made poor eye contact, and had poor social interactions. He sat at 10 months of age, was able to pull to stand at 17 months, but was unable to walk. He was unsteady in his movements. The seizures occurred when he came out of sleep with jerk-like movements of the arms and then generalized shaking. The seizures were unresponsive to various anticonvulsant agents. He would sleep for only 4 to 6 hours per day and was often awake for much of the night.

As your usual way in the past life, you performed the PE and found :
The head circumference was at the 5th percentile and had decreased from the 50th percentile at birth; height and weight were at the 75th percentile. He had poor eye contact, small optic nerves, central hypotonia with peripherally increased tone, decreased but present deep tendon reflexes, down-going plantar responses, and truncal and appendicular ataxia. who else to turn to except the Lab ?

Investigations gave you the following:
The blood glucose level was 70 mg/dL , and the initial lactate level was 6.1 mmol/L (Ouch . . it's high). The lactate measurement was repeated several more times, and the mean level was 4.2 mmol/L; the mean pyruvate level was 0.18 mmol/L . Measurement of serum amino acids showed an increased level of alanine. Ammonia, chromosomes (46 XY), urine organic acids, acylcarnitines, very long chain fatty acids, phytanic acid, and screening tests for Smith-Lemli-Opitz syndrome were all normal.
you went for muscle biopsy and found results were also normal, including special studies for enzymes of the electron transport chain. Mitochondrial DNA analysis was normal. Electroencephalography showed multifocal spikes and generalized spike-and-wave activity. Findings on magnetic resonance imaging of the head were normal. A skin biopsy specimen failed to show any cytoplasmic inclusions. The electroretinogram was abnormal.

You kept thinking what additional investigation to perform . . at last brain wave tells you to go for southern blot and the only thing that comes as result is abnormal methylation pattern.

Now tell the differentials and suspected diagnosis ?

(don't tell me he's got autism cause i already know)

How are you going to proceed?