Table 2.

Novel genes

Gene	Gene name	ID	Inheritance	Nomenclature	Familial/ sporadic	Age at onseta	Spastic paraparesis	Ataxia		Additional features	Validation strategy
SVBP	Small vasohibin-binding protein	IDSPG8 IDSPG46	Homozygous Homozygous	p.(Leu49Pro) p.(Leu49Pro)	Familial Familial	162	YesNo	NoNo	Intellectual disability Axonal sensorimotor peripheral neuropathy		Transfection assay, Western blot and Immunofluorescence
PI4KA	Phosphatidylinositol 4-kinase, catalytic, alpha	IDSPG16 IDSPG149	Compound Heterozygous Compound Heterozygous	p.(Thr2053SerfsTer4)/ p.(Glu1820del) p.(Val1556Met)/ p.(Thr1720Ile)	Sporadic Sporadic	173	YesYes	NoNo	No Learning difficulty		Targeted lipidomics, Western blot and Immunofluorescence [38]
SHMT2	Serine hydroxymethyl transferase, mitochondrial	IDSPG26	Homozygous	p.(Pro499Ala)	Familial	1	Yes	No	Global developmental delay, hypoplastic corpus callosum		Targeted metabolomics and mitochondrial redox metabolism [39]
PCYT2	Phosphate cytidylyltransferase 2, ethanolamine	IDSPG27	Homozygous	p.(Lys319Asn)	Sporadic	19	Yes	Yes	Distal hereditary motor neuropathy		Targeted lipidomics and cDNA analysis [40]
UBAP1	Ubiquitin-associated protein 1	IDSPG76	Heterozygous	p.(Phe159Ter)	Familial	7	Yes	No	Attention deficit hyperactivity disorder		Truncating variant published with 4 additional families, 3 affected relatives [41]
DLG4	Discs large Maguk scaffold protein 4	IDSPG109	Heterozygous	c.1721-1G > A	Sporadic	1	Yes	Yes	Learning difficulty, bradykinesia, dystonia, myoclonus		Truncating variant published with 52 additional families [42]
SLC35B2	Solute carrier family 35 (3-prime-phosphoadenosine 5-prime-phosphosulfate transporter), Member B2	IDLNF68	Homozygous	c.1224_1225delAG	Sporadic	0	Yes	No	Intellectual disability		Truncating variant, validated through qRT-PCR, WB, transfection assay [45]

Validated candidate genes, clinical features of affected individuals

^a Age in years