Is SYN1 p.His657= (c.1971C>T) pathogenic?

SYN1 p.His657= (c.1971C>T) is classified Likely benign in SYN1 (ClinVar, Multiple submitters, 3 submitters; last evaluated 2024-12-07). Very rare (popmax 0.00899%, nfe); Associated with epilepsy, X-linked 1, with variable learning disabilities and behavior disorders.

How common is SYN1 p.His657= (c.1971C>T) in the general population?

SYN1 p.His657= (c.1971C>T) is very rare (popmax 0.00899%, nfe) (gnomAD).

SYN1 p.His657=

Q: What condition is associated with SYN1 p.His657= (c.1971C>T)?

SYN1 p.His657= (c.1971C>T) is associated with epilepsy, X-linked 1, with variable learning disabilities and behavior disorders (ClinVar).

Q: How is X-linked epilepsy-learning disabilities-behavior disorders syndrome inherited?

Typically X-linked recessive (Orphanet). A genetic counselor can assess individual risk for a family.

c.1971C>T · rs201236500 · VCV1159939

Likely benign Multiple submitters

Classification

Likely benign

ClinVar

Review

Multiple submitters ★★☆☆

ClinVar · 3 submitters

gnomAD v4.1

Rare

very rare (popmax 0.00899%, nfe)

Conditions

epilepsy, X-linked 1, with variable learning disabilities and behavior disorders

Computational evidence

Protein change
Missense predictors do not apply to this variant type; conservation carries the signal.
Splicing
SpliceAI	—	not assessed · no allele here is in the release
Constraint at this position
Conservation	phyloP 3.5	phastCons 1
Overall
CADD	9.305	PHRED · no single calibrated threshold — expert panels disagree

Population frequency

gnomAD v4.1 · exomes + genomes

Grpmax group 0.00899% European (non-Finnish) · 78/867,413 alleles

Filtering AF 0.00732% ClinGen BA1/BS1 input FAF95, joint · FAF99 0.00677%

Overall 0.00682% 78/1,144,075 alleles · very rare exomes 74/1,031,353 · genomes 4/112,722 · joint denominator

Rarity supports pathogenicity (ACMG PM2); frequency above a disease-specific BA1/BS1 threshold argues against it. A variant frequent in one ancestry group can be near-absent in others, so a single global figure can mislead.

Variant & gene context

Gene: SYN1
Protein: p.His657=
Coding: c.1971C>T
MANE Select: NM_006950
dbSNP: rs201236500
Type: single nucleotide variant
Location: chrX:47574013 (GRCh38)
Structure: AlphaFold pLDDT 69.86
Residue 657: the 'disordered' region; a UniProt-annotated variant site (in xlid50; affects excitatory and inhibitory synaptic transmission leading to neuronal hyperexcitability; fails to rescue defective synaptic vesicle exocytosis in syn1-knockout mouse neurons; results in severely decreased phosphorylation by camk2 and mapk1; results in delayed axon elongation when tested in syn1-knockout mouse neurons; severely reduced interaction with syn2; has no effect on protein targeting to presynapse); the 'e' region

Full SYN1 gene report on Sugi Atlas → Gene function, pathways, protein structure, interactions & more

Disease context

epilepsy, X-linked 1, with variable learning disabilities and behavior disorders — disease report on Sugi Atlas → Associated genes, phenotypes, clinical trials & treatments

For X-linked epilepsy-learning disabilities-behavior disorders syndrome (Orphanet):

Inheritance: X-linked recessive
Onset: Childhood

Similar variants

SYN1 p.His657Pro Uncertain significance ★★ ⚠ same residue
SYN1 c.528-2A>T Pathogenic/Likely pathogenic ★★ same condition
SYN1 c.838-2A>G Likely pathogenic ★★ same condition
SYN1 p.Arg234Ter Pathogenic ★★ same condition
SYN1 p.Arg420Gln Likely pathogenic ★★ ⚠ same condition
SYN1 p.Arg422Ter Pathogenic ★★ same condition
SYN1 p.Gln483Ter Pathogenic ★★ same condition
SYN1 p.Gln555Ter Pathogenic ★★ same condition

Built on 18 open, versioned datasets — ClinVar, gnomAD, AlphaMissense, REVEL, ClinGen & more — plus Sugi Variant's own cross-source analysis. Source data 2026-01–2026-10, ClinVar 2026-10. Full sources & versions →

Cite Sugi Variant

Gür T. Sugi Variant: A Deterministic Per-Variant Germline Reference from a Knowledge Graph for Humans and AI Agents. 2026. doi:10.5281/zenodo.21509445. This variant: https://sugi.bio/variant/syn1-p-his657 (accessed [today's date]).

Preprint & method: sugi.bio/variant/method Machine-readable: this page as Markdown