Mitochondrial diseases mimicking neurotransmitter defects.

Objectives: Mitochondrial disorders are clinically heterogeneous. We aimed to describe 5 patients who presented with a clinical picture suggestive of primary neurotransmitter defects but who finally fulfilled diagnostic criteria for mitochondrial disease.

Methods: We report detailed clinical features, brain magnetic resonance findings and biochemical studies, including cerebrospinal fluid (CSF) biogenic amine and pterin measurements, respiratory chain enzyme activity, and molecular studies.

Results: The 5 patients had a very early onset age (from 1 day to 3 months) and a severe clinical course. They all showed a clinical picture suggestive of infantile hypokinetic-rigid syndrome (hypokinesia, hypomimia, slowness of reactions, tremor), other abnormal movements (myoclonus, dystonia), axial hypotonia, limb hypertonia, feeding difficulties, and psychomotor delay. Abnormal CSF findings among the 4 patients without treatment included low levels of homovanillic acid (HVA) in 3 patients, with associated low 5-hydroxyindoleacetic acid (5-HIAA) concentrations in two of them. Absent or mild and transitory improvement was observed after treatment with L-dopa. A diagnosis of mitochondrial disorder was finally made due to the appearance of hyperlactacidemia, diverse respiratory chain defects, and multisystemic involvement.

Conclusions: Secondary neurotransmitter disturbances may occur in mitochondrial diseases. Differential diagnosis of hypokinetic-rigid syndrome presenting in infancy could also include paediatric mitochondrial disorders.