Is CTPS1 p.Ser300= (c.900T>C) pathogenic?

CTPS1 p.Ser300= (c.900T>C) is classified Likely benign in CTPS1 (ClinVar, Single submitter, 1 submitter; last evaluated 2025-12-27). Ultra-rare (popmax 0.0183%, amr); Associated with combined immunodeficiency due to CTPS1 deficiency.

What condition is associated with CTPS1 p.Ser300= (c.900T>C)?

CTPS1 p.Ser300= (c.900T>C) is associated with combined immunodeficiency due to CTPS1 deficiency (ClinVar).

How common is CTPS1 p.Ser300= (c.900T>C) in the general population?

CTPS1 p.Ser300= (c.900T>C) is ultra-rare (popmax 0.0183%, amr) (gnomAD).

CTPS1 p.Ser300=

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.900T>C · rs776135557 · VCV1101690

Likely benign Single submitter

Classification

Likely benign

ClinVar

Review

Single submitter ★☆☆☆

ClinVar · 1 submitter

gnomAD v4.1

Rare

ultra-rare (popmax 0.0183%, amr)

Conditions

combined immunodeficiency due to CTPS1 deficiency

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 -0.93	GERP -5.2, phastCons 0.008
Overall
CADD	6.497	PHRED · no single calibrated threshold — expert panels disagree

Population frequency

gnomAD v4.1 · exomes + genomes

Grpmax group 0.0183% Admixed American · 11/60,000 alleles

Filtering AF 0.0102% ClinGen BA1/BS1 input FAF95, joint · FAF99 0.00785%

Overall 0.000753% 11/1,461,734 alleles · ultra-rare

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.Ser300=
Coding: c.900T>C
MANE Select: NM_001905
dbSNP: rs776135557
Type: single nucleotide variant
Location: chr1:40997421 (GRCh38)
Gene constraint: LOEUF 0.423 · pLI 1.00 (gnomAD)
Structure: AlphaFold pLDDT 91.46 · 7 PDB
Residue 300: the glutamine amidotransferase type-1 domain; a β-strand

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 p.Ser300Cys Conflicting classifications of pathogenicity ★ ⚠ same residue
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

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-ser300 (accessed [today's date]).

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