A growing body of evidence suggests an association between 
microdeletion/microduplication and schizophrenia/intellectual disability. 
Abnormal neurogenesis and neurotransmission have been implicated in the 
pathogenesis of these neuropsychiatric and neurodevelopmental disorders. The 
kainate/AMPA-type ionotropic glutamate receptor (GRIK = glutamate receptor, 
ionotropic, kainate) plays a critical role in synaptic potentiation, which is an 
essential process for learning and memory. Among the five known GRIK family 
members, haploinsufficiency of GRIK1, GRIK2, and GRIK4 are known to cause 
developmental delay, whereas the roles of GRIK3 and GRIK5 remain unknown. 
Herein, we report on a girl who presented with a severe developmental delay 
predominantly affecting her language and fine motor skills. She had a 2.6-Mb 
microdeletion in 1p34.3 involving GRIK3, which encodes a principal subunit of 
the kainate-type ionotropic glutamate receptor. Given its strong expression 
pattern in the central nervous system and the biological function of GRIK3 in 
presynaptic neurotransmission, the haploinsufficiency of GRIK3 is likely to be 
responsible for the severe developmental delay in the proposita. A review of 
genetic alterations and the phenotypic effects of all the GRIK family members 
support this hypothesis. The current observation of a microdeletion involving 
GRIK3, a kainate-type ionotropic glutamate receptor subunit, and the 
neurodevelopmental manifestation in the absence of major dysmorphism provides 
further clinical implication of the possible role of GRIK family glutamate 
receptors in the pathogenesis of developmental delay.