Is ALG2 p.Thr255Ile (c.764C>T) pathogenic?

ALG2 p.Thr255Ile (c.764C>T) is classified Uncertain significance in ALG2 (ClinVar, Single submitter, 1 submitter; last evaluated 2024-05-06). AlphaMissense: likely benign (0.1612); Very rare (popmax 0.00833%, amr); Associated with congenital myasthenic syndrome 14.

What condition is associated with ALG2 p.Thr255Ile (c.764C>T)?

ALG2 p.Thr255Ile (c.764C>T) is associated with congenital myasthenic syndrome 14, ALG2-congenital disorder of glycosylation (ClinVar).

How common is ALG2 p.Thr255Ile (c.764C>T) in the general population?

ALG2 p.Thr255Ile (c.764C>T) is very rare (popmax 0.00833%, amr) (gnomAD).

How is ALG2-CDG inherited?

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

What do computational predictors say about ALG2 p.Thr255Ile (c.764C>T)?

AlphaMissense predicts likely benign (score 0.1612) — an in-silico prediction, not a clinical call.

ALG2 p.Thr255Ile

c.764C>T · rs766853240 · VCV1491862

Uncertain significance Single submitter

Classification

Uncertain significance

ClinVar

Review

Single submitter ★☆☆☆

ClinVar · 1 submitter

AlphaMissense

likely benign

0.1612 · ACMG-weighted

gnomAD v4.1

Rare

very rare (popmax 0.00833%, amr)

Missense predictors

0/3 damaging

AlphaMissense, REVEL, SaProt

Conditions

congenital myasthenic syndrome 14

Computational evidence

Protein change
AlphaMissense	0.1612	likely benign
REVEL	0.188	benign-leaning
SaProt	LLR -9.07	tolerated
⇒ AlphaMissense, REVEL and SaProt all call this tolerated.
Splicing
SpliceAI	—	not assessed · no allele here is in the release
Constraint at this position
Conservation	phyloP 7.2	GERP 2.5, phastCons 1
Regional constraint	o/e 1.09	unconstrained · MANE · 3,957 bp · p 0.038 · regional, not allelic
Overall
CADD	20.4	PHRED · no single calibrated threshold — expert panels disagree

ClinVar classifies this uncertain; the computational predictors unanimously lean tolerated — a triage signal, not a reclassification

AlphaMissense carries the ACMG weight for missense; REVEL and SaProt are independent agreement signals.

Population frequency

gnomAD v4.1 · exomes + genomes

Grpmax group 0.00833% Admixed American · 5/60,010 alleles

Filtering AF 0.00323% ClinGen BA1/BS1 input FAF95, joint · FAF99 0.00207%

Overall 0.000372% 6/1,614,104 alleles · very rare

Ancestry group	Frequency	1 in
Admixed Americangrpmax	0.00833%	12,002
European (non-Finnish)	8.47e-05%	1,180,052

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: ALG2
Protein: p.Thr255Ile
Coding: c.764C>T
MANE Select: NM_033087
dbSNP: rs766853240
Type: single nucleotide variant
Location: chr9:99218421 (GRCh38)
Gene constraint: LOEUF 1.408 · pLI <0.01 · ClinGen HI gene assoc. with recessive phenotype (gnomAD)
Structure: AlphaFold pLDDT 91.03

Full ALG2 gene report on Sugi Atlas → Gene function, pathways, protein structure, interactions & more

Disease context

congenital myasthenic syndrome 14 — disease report on Sugi Atlas → Associated genes, phenotypes, clinical trials & treatments

Also linked: ALG2-congenital disorder of glycosylation

For ALG2-CDG (Orphanet):

Inheritance: Autosomal recessive
Onset: Infancy, Neonatal

Similar variants

ALG2 p.Ala29Pro Uncertain significance ★★ ⚠ same condition
ALG2 p.Ala36Val Uncertain significance ★★ ⚠ same condition
ALG2 p.Ala71Gly Uncertain significance ★★ ⚠ same condition
ALG2 p.Ala71Val Uncertain significance ★★ ⚠ same condition
ALG2 p.Arg129Gln Uncertain significance ★★ ⚠ same condition
ALG2 p.Arg130Gln Uncertain significance ★★ ⚠ same condition
ALG2 p.Arg251His Uncertain significance ★★ ⚠ same condition
ALG2 p.Arg378Cys Uncertain significance ★★ ⚠ 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/alg2-p-thr255ile (accessed [today's date]).

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