Is CTPS1 p.Ile121Val (c.361A>G) pathogenic?

CTPS1 p.Ile121Val (c.361A>G) is classified Uncertain significance in CTPS1 (ClinVar, Multiple submitters, 2 submitters; last evaluated 2025-03-19). AlphaMissense: likely benign (0.1243); Very rare (popmax 0.008%, afr); Associated with combined immunodeficiency due to CTPS1 deficiency.

What condition is associated with CTPS1 p.Ile121Val (c.361A>G)?

CTPS1 p.Ile121Val (c.361A>G) is associated with combined immunodeficiency due to CTPS1 deficiency (ClinVar).

How common is CTPS1 p.Ile121Val (c.361A>G) in the general population?

CTPS1 p.Ile121Val (c.361A>G) is very rare (popmax 0.008%, afr) (gnomAD).

What do computational predictors say about CTPS1 p.Ile121Val (c.361A>G)?

AlphaMissense predicts likely benign (score 0.1243) — an in-silico prediction, not a clinical call.

CTPS1 p.Ile121Val

Q: How is Severe combined immunodeficiency due to CTPS1 deficiency inherited?

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

c.361A>G · rs200274195 · VCV1373764

Uncertain significance Multiple submitters

Classification

Uncertain significance

ClinVar

Review

Multiple submitters ★★☆☆

ClinVar · 2 submitters

AlphaMissense

likely benign

0.1243 · ACMG-weighted

gnomAD v4.1

Rare

very rare (popmax 0.008%, afr)

Missense predictors

0/3 damaging

AlphaMissense, REVEL, SaProt

Conditions

combined immunodeficiency due to CTPS1 deficiency

Computational evidence

Protein change
AlphaMissense	0.1243	likely benign
REVEL	0.198	benign-leaning
SaProt	LLR -7.95	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 6.2	GERP 0.51, phastCons 1
Regional constraint	o/e 0.68	unconstrained · MANE · 2,623 bp · p 0.0011 · regional, not allelic
Overall
CADD	20.1	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 0.008% African / African-American · 6/75,040 alleles

Filtering AF 0.00347% ClinGen BA1/BS1 input FAF95, joint · FAF99 0.00228%

Overall 0.00192% 31/1,613,996 alleles · very rare

Ancestry group	Frequency	1 in
African / African-Americangrpmax	0.008%	12,507
East Asian	0.00223%	44,878
South Asian	0.0022%	45,535
European (non-Finnish)	0.00186%	53,631

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: CTPS1
Protein: p.Ile121Val
Coding: c.361A>G
MANE Select: NM_001905
dbSNP: rs200274195
Type: single nucleotide variant
Location: chr1:40987395 (GRCh38)
Gene constraint: LOEUF 0.423 · pLI 1.00 (gnomAD)
Structure: AlphaFold pLDDT 91.46 · 7 PDB
Residue 121: an α-helix

Full CTPS1 gene report on Sugi Atlas → Gene function, pathways, protein structure, interactions & more

Disease context

combined immunodeficiency due to CTPS1 deficiency — disease report on Sugi Atlas → Associated genes, phenotypes, clinical trials & treatments

For Severe combined immunodeficiency due to CTPS1 deficiency (Orphanet):

Inheritance: Autosomal recessive
Onset: Childhood, Infancy, Neonatal

Similar variants

CTPS1 c.1692-1G>C Pathogenic ★★ same condition
CTPS1 c.1095-5T>G Uncertain significance ★★ same condition
CTPS1 p.Ala471Thr Uncertain significance ★★ ⚠ same condition
CTPS1 p.Arg102Trp Uncertain significance ★★ ⚠ same condition
CTPS1 p.Arg294His Uncertain significance ★★ ⚠ same condition
CTPS1 p.Arg376Gln Uncertain significance ★★ ⚠ same condition
CTPS1 p.Arg550Gln Uncertain significance ★★ ⚠ same condition
CTPS1 p.Asn412Ser 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/ctps1-p-ile121val (accessed [today's date]).

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