Background:

Megalencephalic leukoencephalopathy with subcortical cysts is a rare type of leukodystrophy associated with mutations in the MLC1 and GlialCAM genes. The classic form is characterized by macrocephaly, early or delayed normal neurodevelopment followed by a period of slow motor skill loss, with cerebellar ataxia and spasticity; some patients develop movement disorders and seizures. Magnetic resonance imaging shows widespread diffuse white matter involvement with edema and subcortical cysts

Case report:

We describe the case of two sisters aged 6 and 10 years, consanguineous parents, with a history of psychomotor delay and macrocephaly. The older sister presented with seizures at the age of 4 years and spasticity without loss of gait; the younger sister had a similar clinical picture. Magnetic resonance imaging showed diffuse alteration of the white matter and subcortical cysts in the temporal lobes. Electroencephalogram detected focal epileptiform activity. Seizure control was achieved upon initiation of carbamazepine treatment. By sequencing, a homozygous variant of the MLC1 gene was found in exon 3: c.255T>G (p.Cys85Trp)

Conclusions:

Leukodystrophies are rare diseases that represent a diagnostic challenge. Clinical, radiological, and molecular findings allow diagnostic certainty, the appropriate direction of interventions, and adjustment to the prognosis of each entity. The c.255T>G mutation was previously described in a South American patients, suggesting that it is a specific variant to Latin populations.