Early Myoclonic Encephalopathy

A rare disorder characterized clinically by the onset of fragmentary myoclonus appearing in the first month of life, often associated with erratic focal seizures and a suppression-burst EEG pattern.

Epidemiology

The prevalence is unknown but Early myoclonic encephalopathy is a rare disease with only around 30 cases described so far.

Clinical description

Onset sometimes occurs as early as a few hours after birth, and postnatal movements are sometimes reported by the mother to be of the same type as those felt at the end of pregnancy. Other types of seizures, including partial seizures, massive myoclonia, and tonic spasms can also occur; usually at around 3-4 months of age. Neurological abnormalities are constant: very severe delay in psychomotor acquisitions, marked hypotonia, and disturbed alertness, sometimes with a vegetative state. Signs of peripheral neuropathy may also occur in rare cases.

Etiology

Although the etiology is mostly unknown, nonketotic hyperglycinemia, pyridoxine or pyridoxal-phosphate dependency, together with congenital deficiency of the mitochondrial glutamate transporter are known to produce a similar clinical picture. Therefore, this condition may result from excess glutamate delivery in the synaptic cleft by the end of pregnancy.

Genetic counseling

There is a high risk of familial recurrence since in most cases the disease appears to be inherited as an autosomal recessive trait.

Management and treatment

There is no effective treatment.

Prognosis

The prognosis is poor: children with the condition survive in a persistent vegetative state or die within the first or second year of life.