Is MEF2C p.Ser340= (c.1020C>T) pathogenic?

MEF2C p.Ser340= (c.1020C>T) is classified Likely benign in MEF2C (ClinVar, Multiple submitters, 2 submitters; last evaluated 2021-08-29). Very rare (popmax 0.00519%, nfe); Associated with neurodevelopmental disorder with hypotonia, stereotypic hand movements, and impaired language.

How common is MEF2C p.Ser340= (c.1020C>T) in the general population?

MEF2C p.Ser340= (c.1020C>T) is very rare (popmax 0.00519%, nfe) (gnomAD).

MEF2C p.Ser340=

Q: What condition is associated with MEF2C p.Ser340= (c.1020C>T)?

MEF2C p.Ser340= (c.1020C>T) is associated with neurodevelopmental disorder with hypotonia, stereotypic hand movements, and impaired language (ClinVar).

c.1020C>T · rs756799434 · VCV916274

Likely benign Multiple submitters

Classification

Likely benign

ClinVar

Review

Multiple submitters ★★☆☆

ClinVar · 2 submitters

gnomAD v4.1

Rare

very rare (popmax 0.00519%, nfe)

Conditions

neurodevelopmental disorder with hypotonia, stereotypic hand movements, and impaired language

Computational evidence

Protein change
Missense predictors do not apply to this variant type; conservation carries the signal.
Splicing
SpliceAI	<0.2	no splice effect predicted · four deltas, not one · how we know
Constraint at this position
Conservation	phyloP 0.98	GERP -0.04, phastCons 1
Overall
CADD	12.85	PHRED · no single calibrated threshold — expert panels disagree

Population frequency

gnomAD v4.1 · exomes + genomes

Grpmax group 0.00519% European (non-Finnish) · 59/1,136,188 alleles

Filtering AF 0.00409% ClinGen BA1/BS1 input FAF95, joint · FAF99 0.00374%

Overall 0.00411% 63/1,532,640 alleles · very rare exomes 60/1,380,470 · genomes 3/152,170 · joint denominator

Ancestry group	Frequency	1 in
European (non-Finnish)grpmax	0.00519%	19,257
Admixed American	0.00399%	25,053
African / African-American	0.00138%	72,540
South Asian	0.00125%	80,304

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: MEF2C
Protein: p.Ser340=
Coding: c.1020C>T
MANE Select: NM_002397
dbSNP: rs756799434
Type: single nucleotide variant
Location: chr5:88728573 (GRCh38)
Gene constraint: LOEUF 0.212 · pLI 1.00 · ClinGen HI 3/3 (gnomAD)
Structure: AlphaFold pLDDT 56.80

Full MEF2C gene report on Sugi Atlas → Gene function, pathways, protein structure, interactions & more

Disease context

neurodevelopmental disorder with hypotonia, stereotypic hand movements, and impaired language — disease report on Sugi Atlas → Associated genes, phenotypes, clinical trials & treatments

Similar variants

MEF2C c.638-1G>A Pathogenic/Likely pathogenic ★★ same condition
MEF2C c.638-2A>C Pathogenic ★★ same condition
MEF2C c.965-2A>G Pathogenic ★★ same condition
MEF2C c.-26C>T Pathogenic ★★ same condition
MEF2C c.-8C>T Pathogenic ★★ same condition
MEF2C p.Arg15Cys Pathogenic/Likely pathogenic ★★ same condition
MEF2C p.Arg15His Pathogenic/Likely pathogenic ★★ same condition
MEF2C p.Arg15Pro 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/mef2c-p-ser340 (accessed [today's date]).

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