Table 2.

Clinical features of individuals harboring GRIK2 missense variants

Proband	Age (years)	Sex	Diagnosis	Motor dysfunction	Hypotonia	Hypertonia	Visual impairment	Seizure onset (age in months)	Myelination
A657T.1a	15	F	ID, DD	ataxia	resolved	N.O.	N.O.	N.O.	normal
A657T.2	8	M	ID, DD	uncoordinated gait	N.O.	N.O.	N.O.	N.O.	N.R.
A657T.3	13	M	ID, DD	uncoordinated gait	N.O.	N.O.	hypermetropia astigmatism	N.O.	normal
A657T.4	7	M	ID, DD, ASD	imbalance	resolved	N.O.	N.O.	N.O.	normal
A657T.5	6	F	ID, DD	ataxia	N.O.	N.O.	N.O.	N.O.	N.R.
A657T.6	37	F	ID, DDb	imbalance	N.O.	truncal and limbs	N.O.	N.O.	normal
T660K.1	5	M	global DD	not ambulatory	truncal	limbs	nystagmus	8	abnormal
T660K.2	2	M	global DD	not ambulatory	N.R.	N.R.	nystagmus	7	abnormal
T660K.3	2	F	global DD	not ambulatory	truncal	limbs	CVI	8	abnormal
T660R.1	4	F	global DD	limited function (standing only)	truncal	N.O.	CVI	27	abnormal
T660R.2	12	M	ID, DD	ataxia	resolved	N.O.	strabismus	N.O.c	abnormal
I668T.1	12	M	ASD	N.R.	N.O.	N.O.	N.R.	N.O.	N.R.

F, female; M, male; ASD, autism spectrum disorder; CVI, cortical visual impairment; DD, developmental motor and speech delay; ID, intellectual disability; N.O., not observed; N.R., not reported.

^aProband A657T.1 was reported in an earlier study¹⁷ and is included for comparative purposes.

^bProband A657T.6: autistiform behaviors were observed, but ASD was not formally diagnosed.

^cProband T660R.2: definitive seizures have not been observed, but the child did exhibit a single event during which he became unresponsive and his eyes deviated upward.