Is CHAT p.Arg66= (c.198C>T) pathogenic?

CHAT p.Arg66= (c.198C>T) is classified Likely benign in CHAT (ClinVar, Single submitter, 1 submitter; last evaluated 2024-01-02). Very rare (popmax 0.00119%, sas); Associated with congenital myasthenic syndrome 6.

What condition is associated with CHAT p.Arg66= (c.198C>T)?

CHAT p.Arg66= (c.198C>T) is associated with congenital myasthenic syndrome 6 (ClinVar).

How common is CHAT p.Arg66= (c.198C>T) in the general population?

CHAT p.Arg66= (c.198C>T) is very rare (popmax 0.00119%, sas) (gnomAD).

CHAT p.Arg66=

c.198C>T · rs1230433889 · VCV1582439

Likely benign Single submitter

Classification

Likely benign

ClinVar

Review

Single submitter ★☆☆☆

ClinVar · 1 submitter

gnomAD v4.1

Rare

very rare (popmax 0.00119%, sas)

Conditions

congenital myasthenic syndrome 6

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 1.4	GERP 0.13, phastCons 0.004
Overall
CADD	9.934	PHRED · no single calibrated threshold — expert panels disagree

Population frequency

gnomAD v4.1 · exomes + genomes

Grpmax group 0.00119% South Asian · 1/83,800 alleles

Filtering AF 2.9e-05% ClinGen BA1/BS1 input FAF95, joint · FAF99 1.1e-05%

Overall 0.000194% 3/1,544,604 alleles · very rare exomes 2/1,392,402 · genomes 1/152,202 · joint denominator

Ancestry group	Frequency	1 in
South Asiangrpmax	0.00119%	83,800
European (non-Finnish)	0.000175%	572,197

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: CHAT
Protein: p.Arg66=
Coding: c.198C>T
MANE Select: NM_020549
dbSNP: rs1230433889
Type: single nucleotide variant
Location: chr10:49614387 (GRCh38)
Gene constraint: LOEUF 0.973 · pLI <0.01 · ClinGen HI gene assoc. with recessive phenotype (gnomAD)
Structure: AlphaFold pLDDT 84.73 · 8 PDB
Residue 66: the 'disordered' region

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

Disease context

congenital myasthenic syndrome 6 — disease report on Sugi Atlas → Associated genes, phenotypes, clinical trials & treatments

Similar variants

CHAT p.Arg66Ser Uncertain significance ★ ⚠ same residue
CHAT p.Arg66fs Conflicting classifications of pathogenicity ★ same residue
CHAT p.Arg66Cys Uncertain significance ★ ⚠ same residue
CHAT c.1282-2A>T Likely pathogenic ★★ same condition
CHAT c.1840-9A>G Pathogenic/Likely pathogenic ★★ same condition
CHAT c.698+1G>T Likely pathogenic ★★ same condition
CHAT c.698+2T>C Likely pathogenic ★★ same condition
CHAT p.Ala557Thr Pathogenic/Likely 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/chat-p-arg66 (accessed [today's date]).

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