PEHO syndrome: KIF1A mutation and decreased activity of mitochondrial respiratory chain complex.

We report a child with hypotonia, optic atrophy, progressive encephalopathy and intractable infantile spasms who was diagnosed with PEHO syndrome. Extensive investigation was performed to diagnose an underlying etiology. Electron transport chain activities in muscle biopsies showed an isolated complex IV deficiency. Genetic examination focused on complex IV genes such as mtDNA and relevant nuclear DNA analysis was unremarkable. Whole exome sequencing with trio revealed a heterozygous de novo mutation at c.757G>A (p.E253K) in the KIF1A gene. The protein encoded by this gene functions as an anterograde motor protein that transports membranous organelles along axonal microtubules. The relation between this genetic mutation and decreased activity of the mitochondrial respiratory chain complex is discussed in details. Our study further confirmed that the molecular basis of PEHO syndrome at least in a subset of patients is a dominant KIF1A variant affecting the motor domain of the protein. This is the first description of the decreased activity of mitochondrial respiratory chain complex in association with either PEHO syndrome or KIF1A mutation. This study emphasizes that the results of the mitochondrial enzymes should be interpreted with caution and clinicians should be actively looking for other underlying diagnoses with further comprehensive studies.