Kleefstra syndrome is a rare neurogenetic disorder caused by a subtelomeric 
9q34.3 deletion or by an intragenic mutation of the euchromatin histone methyl 
transferase 1 gene (EHMT1). Approximately 20% to 30% of individuals have hearing 
loss. The left temporal bone of one subject with hearing loss was studied using 
light microscopy. There were several abnormalities including dysostosis of the 
stapes without fixation, enlarged vestibular aqueduct, anomalies of the organ of 
Corti in the basal turn, cyst formation in the stria vascularis, and dysmorphia 
of the cochlear modiolus and the vestibular labyrinth. This is the first 
published description of the otopathology in Kleefstra syndrome. Laryngoscope, 
130:2028-2033, 2020.