TABLE 1B.

Clinical and genetic findings in novel and previously published individuals with PIGT deficiency harboring the p.Asn527Ser or p.Val528Met variant in either homozygous or compound heterozygous state.

Families	Family 11	Family 11	Family 12	Family 13	Family 14	Family 15	Family 16	Family 17	Family 18	Family 19	Family 20	Family 21
	Patient 14	Patient 15	P1 (Jezela-Stanek et al., 2020)	P2 (Jezela-Stanek et al., 2020)	P3 (Jezela-Stanek et al., 2020)	P4 (Jezela-Stanek et al., 2020)	P5 (Jezela-Stanek et al., 2020)	P6 (Jezela-Stanek et al., 2020)	P7 (Jezela-Stanek et al., 2020)	P3 (Bayat et al., 2019)	P10 (Bayat et al., 2019)	Decipher ID 258094 (Pagnamenta et al., 2017)
cDNA change (NM_015937.6)	c.1582G > A; c.1582G > A	c.1582G > A; c.1582G > A	c.1582G > A; c.1582G > A	c.1730dupC; c.1582G > A	c.1520G > A; c.1582G > A	c.494-2A > G; c.1582G > A	c.1582G > A; c.1582G > A	c.1096G > A; c.1582G > A	c.494-2A > G; c.1582G > A	c.494-2A, c.1582G > A;	c.1724_1725insC; c.1582G > A	c.1730dupC; c.1582G > A
Amino acid change (NP_057021.2)	p.Val528Met; p.Val528Met	p.Val528Met; p.Val528Met	p.Val528Met; p.Val528Met	p.Leu578fsTer 35; p.Val528Met	p.Ala507Gly; p.Val528Met	Splice site; p.Val528Met	p.Val528Met; p.Val528Met	p.Gly366TArg; p.Val528Met	Splice site; p.Val528Met	Splice site; p.Val528Met	p.Leu578fsTer35; p.Val528Met	p.Leu578fsTer35; Val528Met
Clinical significance	PATH; PATH	PATH; PATH	PATH; PATH	PATH; PATH	PATH; PATH	PATH; PATH	PATH; PATH	PATH; PATH	PATH; PATH	PATH; PATH	VUS;PATH	PATH; PATH
Heritage	Caucasian	Caucasian	Polish	Polish	Polish	Polish	Polish	Polish	Polish	Polish	Polish	Polish
Age at inclusion	2 years	7.5 years	Born 2019	Born 2017	Born 2017	Born 2016	Born 2011	Born 2013	Born 2003	5 years	4 years	Unknown
Gender	Female	Female	Female	Male	Male	Male	Female	Male	Female	Female	Female	Female
Seizures	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Epilepsy diagnosis	Yes	Yes	No	No	Yes	Yes	Yes	No	No	Yes	Yes	Yes
Age at seizure onset	6 months	20 months	6 months	12 months	6 months	9 months	6 months	11 months	12 months	12 months	18 months	12 months
Non-epileptic myoclonic jerks	Yes	No	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown
Seizure types during disease course	Atypical absences (generalized)	Atypical absences	Fever-induced tonic–clonic seizures of unknown onset	Fever-induced focal seizures with impaired awareness	Focal hypomotor seizures with impaired awareness, FBTCS	Absences, myoclonic jerks, and bilateral tonic–clonic seizures	Focal hypomotor seizures with impaired awareness, FBTCS, and generalized myoclonic jerks	Focal hypomotor seizures with impaired awareness	Focal hypomotor seizures with impaired awareness	Fever-induced tonic–clonic seizures of unknown onset	Bilateral tonic–clonic seizures of unknown onset	Bilateral tonic–clonic seizures of unknown onset
Febrile seizures	No	Yes	Yes (only)	Yes (only)	Yes	Yes	Yes	Yes (only)	Yes	Unknown	Unknown	Unknown
Status epilepticus	No	No	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown
Current AED	LEV	LEV	None	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown
Lifetime AED	LEV	LEV	None	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown
Overall antiepileptic drug response∗	Very good	Very good	Not relevant	Very good	Very good	Poor (intractable myoclonic jerks)	Good	Very good	Very good	Good	Good	Good
Age at sitting	1 year (with support)	3 years	Unable	25 months	18 months	30 months	2.5 years	2 years	2.5 years	Unknown	Unknown	Unknown
Age at walking	Unable	6 years (a few steps)	Unable	Unknown but can walk assisted	Unable	Unable	Unable	Unable	6 years (unassisted but short distances)	Unknown	Unknown	Unknown but can walk
Useful use of hands	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown
Age at first words	Non-verbal	Non-verbal	Unknown	Unknown	Unknown	23 months	3.5 years	4.5 years	5 years	Unknown	Unknown	Unknown
Present verbal ability	Unknown	Understands simple sentences. Uses a communication device with eye movement control for words	Unknown	Unknown	Single words, dysarthria	Single words	Communicates through simple sentences, dysarthria	Single words	Single words, dysarthria	Unknown	Unknown	Unknown
Developmental delay	Severe	Severe	Unable to classify	Unable to classify	Unable to classify	Unable to classify	Unable to classify	Unable to classify	Unable to classify	Unable to classify	Unable to classify	Unable to classify
Autism	Unknown but has limited eye contact	No	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown
Brain MRI results	Not performed	2 years: cerebellar atrophy	6 months: delayed myelination	10 months: delayed myelination, slight enlargement of pericerebral spaces	12 months: decreased white matter volume, enlargement of pericerebral spaces	12 months: decreased cerebral white matter volume including CC; 16 months: cortical–subcortical atrophy	8 months: delayed myelination and slight enlargement of pericerebral spaces; 3 years: cortical–subcortical and cerebellar vermis atrophy	Three times over 1 year: progressive cortical–subcortical atrophy, cerebellar vermis atrophy	12 months: normal; 11 and 16 years: progressive cerebral and cerebellar atrophy	Unknown age: cerebellar atrophy	4 years: progressive isolated cerebellar atrophy	Progressive isolated cerebellar atrophy

*Overall antiepileptic drug response (very good = seizure-free; partially good = partially seizure- free on treatment; and poor = intractable seizures despite treatment). Abbreviations: AED, antiepileptic drug; CBD, cannabidiol; CBZ, carbamazepine; CC, corpus callosum; EEG, electroencephalogram; FBTCS, focal to bilateral tonic–clonic seizure; LEV, levetiracetam; LMT, lamotrigine; MAE, myoclonic atonic epilepsy; MRI, magnetic resonance imaging; MS, myoclonic seizure; PATH, pathogenic; PHT, phenytoin; PIGT, phosphatidylinositol glycan class T protein; PMD, primidone; VPA, valproate; VUS, variant on unknown significance; TPM, topiramate.