Two siblings with psychomotor retardation, congenital hypotonia, spasticity, and 
no speech acquisition underwent MRI and Tc ethyl cysteinate dimer SPECT imaging. 
The SPECT images showed a reduction in regional cerebral blood flow in the 
bilateral frontal cortex and cerebellum in both cases. T2-weighted and fluid 
attenuated inversion recovery images obtained using MRI showed delayed 
myelination and cortical atrophy in mainly the frontal lobes. Based on the MRI 
findings, the abnormal serum levels of thyroid hormone, and the gene mutation, 
the siblings were diagnosed as having monocarboxylate transporter 8 deficiency. 
A reduction in regional cerebral blood flow, as observed using SPECT, may be a 
common feature of monocarboxylate transporter 8 deficiency.