Is ADA p.Ala221Thr (c.661G>A) pathogenic?

ADA p.Ala221Thr (c.661G>A) is classified Uncertain significance in ADA (ClinVar, Single submitter, 2 submitters; last evaluated 2021-08-26). AlphaMissense: likely benign (0.1709); Very rare (popmax 8.47e-05%, nfe); Associated with severe combined immunodeficiency, autosomal recessive, T cell-negative, B cell-negative, NK cell-negative, due to adenosine deaminase deficiency.

How common is ADA p.Ala221Thr (c.661G>A) in the general population?

ADA p.Ala221Thr (c.661G>A) is very rare (popmax 8.47e-05%, nfe) (gnomAD).

What do computational predictors say about ADA p.Ala221Thr (c.661G>A)?

AlphaMissense predicts likely benign (score 0.1709) — an in-silico prediction, not a clinical call.

ADA p.Ala221Thr

Q: What condition is associated with ADA p.Ala221Thr (c.661G>A)?

ADA p.Ala221Thr (c.661G>A) is associated with severe combined immunodeficiency, autosomal recessive, T cell-negative, B cell-negative, NK cell-negative, due to adenosine deaminase deficiency (ClinVar).

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

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

c.661G>A · rs2065347889 · VCV960444

Uncertain significance Single submitter

Classification

Uncertain significance

ClinVar

Review

Single submitter ★☆☆☆

ClinVar · 2 submitters

AlphaMissense

likely benign

0.1709 · ACMG-weighted

gnomAD v4.1

Rare

very rare (popmax 8.47e-05%, nfe)

Missense predictors

0/2 damaging

AlphaMissense, SaProt · REVEL no call

Conditions

severe combined immunodeficiency, autosomal recessive, T cell-negative, B cell-negative, NK cell-negative, due to adenosine deaminase deficiency

Computational evidence

Protein change
AlphaMissense	0.1709	likely benign
REVEL	0.586	indeterminate
SaProt	LLR -9.70	tolerated
⇒ AlphaMissense and SaProt both call this tolerated; REVEL makes no call.
Splicing
SpliceAI	—	not assessed · no allele here is in the release
Constraint at this position
Conservation	phyloP -0.26	GERP 0.38
Regional constraint	o/e 0.94	unconstrained · MANE · 32 kb · p 0.21 · regional, not allelic
Overall
CADD	14.65	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 8.47e-05% European (non-Finnish) · 1/1,180,038 alleles

Overall 6.84e-05% 1/1,461,888 alleles · very 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: ADA
Protein: p.Ala221Thr
Coding: c.661G>A
MANE Select: NM_000022
dbSNP: rs2065347889
Type: single nucleotide variant
Location: chr20:44623024 (GRCh38)
Gene constraint: LOEUF 1.184 · pLI <0.01 (gnomAD)
Structure: AlphaFold pLDDT 96.81 · 2 PDB
Residue 221: an α-helix

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

Disease context

severe combined immunodeficiency, autosomal recessive, T cell-negative, B cell-negative, NK cell-negative, due to adenosine deaminase deficiency — disease report on Sugi Atlas → Associated genes, phenotypes, clinical trials & treatments

For Severe combined immunodeficiency due to adenosine deaminase deficiency (Orphanet):

Inheritance: Autosomal recessive
Onset: Infancy, Neonatal
Prevalence: 1-9 / 1 000 000 (Europe)

Similar variants

ADA p.Ala221= Likely benign ★ same residue
ADA c.1078+2T>A Likely pathogenic ★★★ same condition
ADA c.219-2A>G Likely pathogenic ★★★ same condition
ADA c.363-2A>G Likely pathogenic ★★★ same condition
ADA c.606+1G>T Likely pathogenic ★★★ same condition
ADA c.975+1G>A Pathogenic ★★★ same condition
ADA c.976-1G>C Pathogenic ★★★ same condition
ADA p.Ala329Val 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/ada-p-ala221thr (accessed [today's date]).

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