Is ICOS p.Tyr97Ter (c.291C>A) pathogenic?

ICOS p.Tyr97Ter (c.291C>A) is classified Pathogenic in ICOS (ClinVar, Single submitter, 1 submitter; last evaluated 2025-12-15). Very rare (popmax 0.0011%, nfe); Associated with immunodeficiency, common variable, 1.

What condition is associated with ICOS p.Tyr97Ter (c.291C>A)?

ICOS p.Tyr97Ter (c.291C>A) is associated with immunodeficiency, common variable, 1 (ClinVar).

How common is ICOS p.Tyr97Ter (c.291C>A) in the general population?

ICOS p.Tyr97Ter (c.291C>A) is very rare (popmax 0.0011%, nfe) (gnomAD).

ICOS p.Tyr97Ter

Q: How is Late-onset combined immunodeficiency due to ICOS deficiency inherited?

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

c.291C>A · rs778146668 · VCV2993769

Pathogenic Single submitter

Classification

Pathogenic

ClinVar

Review

Single submitter ★☆☆☆

ClinVar · 1 submitter

Consequence

nonsense (stop-gain)

predicted LoF

gnomAD v4.1

Rare

very rare (popmax 0.0011%, nfe)

Conditions

immunodeficiency, common variable, 1

Computational evidence

Protein change
Missense predictors do not apply to this variant type; conservation carries the signal.
Consequence	nonsense (stop-gain)	predicted loss-of-function
NMD	predicted	premature termination codon in exon 2 of 5
Splicing
SpliceAI	<0.2	all four deltas below 0.2 · C>G here scores Δ0.88 · evaluated, not missing
Constraint at this position
Conservation	phyloP -1.5	GERP -3.5
Overall
CADD	25.7	PHRED · no single calibrated threshold — expert panels disagree

Predicted loss-of-function is descriptive, not an applied PVS1 code.

Population frequency

gnomAD v4.1 · exomes + genomes

Grpmax group 0.0011% European (non-Finnish) · 13/1,179,674 alleles

Filtering AF 0.000615% ClinGen BA1/BS1 input FAF95, joint · FAF99 0.000474%

Overall 0.000958% 14/1,461,412 alleles · very rare

Ancestry group	Frequency	1 in
Remaining individualsnot grpmax-eligible	0.0016%	62,480
European (non-Finnish)grpmax	0.0011%	90,744

Remaining individuals shows a higher raw frequency than the grpmax group above it. gnomAD excludes bottlenecked groups — Finnish, Ashkenazi Jewish, Amish and “Remaining individuals” — from grpmax, because founder effects make their frequencies unrepresentative for filtering. The table is sorted by frequency, so an excluded group can sit above the grpmax row.

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: ICOS
Protein: p.Tyr97Ter
Coding: c.291C>A
MANE Select: NM_012092
dbSNP: rs778146668
Type: single nucleotide variant
Location: chr2:203955868 (GRCh38)
Gene constraint: LOEUF 1.273 · pLI <0.01 (gnomAD)
Structure: AlphaFold pLDDT 74.24 · 2 PDB
Residue 97: the ig-like v-type domain; a disulfide bond

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

Disease context

immunodeficiency, common variable, 1 — disease report on Sugi Atlas → Associated genes, phenotypes, clinical trials & treatments

For Late-onset combined immunodeficiency due to ICOS deficiency (Orphanet):

Inheritance: Autosomal recessive

Similar variants

ICOS c.58+1G>A Likely pathogenic ★★ same condition
ICOS c.59-3C>T Uncertain significance ★★ same condition
ICOS p.Gln134Pro Uncertain significance ★★ ⚠ same condition
ICOS p.Gly24Val Uncertain significance ★★ ⚠ same condition
ICOS p.Gly36Arg Uncertain significance ★★ ⚠ same condition
ICOS p.Ile77Val Uncertain significance ★★ ⚠ same condition
ICOS p.Ser171Tyr Uncertain significance ★★ ⚠ same condition
ICOS p.Thr195Ile 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/icos-p-tyr97ter (accessed [today's date]).

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