A 15-year-old boy with epilepsy on treatment with a combination of valproate and phenytoin has good control of seizures. Levels of both drugs are in the therapeutic range. All of the following adverse effects can be attributed to valproate except -
Weight gain of 5 kg
Serum alanine aminotransaminase 150 IU/L
Rise in serum ammonia level by 20 g/dl
Lymphadenopathy