Abstract
Nonketotic hyperglycinemia (NKH) is an autosomal recessive inborn error in the glycine
degradation pathway resulting in severe neurological impairment with intractable seizures
and brain damage in the majority of the affected patients. Depending on the age of
onset and on the outcome of the disease, severe and attenuated forms of NKH may be
discriminated. During neonatal period, patients may present with early myoclonic encephalopathy;
in the course of the disease, the picture of seizures changes, and multiple forms
of seizures may occur. In patients with severe NKH, seizures remain persistent and
resistant to anticonvulsant treatment. Variant NKH, caused by mutations resulting
in a deficiency of the cofactor lipoate, may lead to a clinical picture resembling
severe NKH. Therapy of NKH is directed at decreasing glycine concentrations and at
blocking the effect of glycine at the neurotransmitter receptors. Additionally, combined
anticonvulsive treatment is necessary in most children with NKH, mainly in those with
severe NKH. A few anticonvulsants have shown to be partial effective in patients with
NKH. However, all reports on anticonvulsive treatment in NKH are single case reports
and no long-term studies have been performed in this patient's cohort. Hence, no recommendations
for the treatment of epilepsy in NKH are yet available.
Keywords
Nonketotic hyperglycinemia - glycine encephalopathy - myoclonic encephalopathy - epilepsy
