Is QDPR p.Arg221Ter (c.661C>T) pathogenic?

QDPR p.Arg221Ter (c.661C>T) is classified Pathogenic in QDPR (ClinVar, Multiple submitters, 4 submitters; last evaluated 2026-02-06). Very rare (popmax 0.00167%, amr); Associated with dihydropteridine reductase deficiency.

What condition is associated with QDPR p.Arg221Ter (c.661C>T)?

QDPR p.Arg221Ter (c.661C>T) is associated with dihydropteridine reductase deficiency (ClinVar).

How common is QDPR p.Arg221Ter (c.661C>T) in the general population?

QDPR p.Arg221Ter (c.661C>T) is very rare (popmax 0.00167%, amr) (gnomAD).

QDPR p.Arg221Ter

Q: How is Hyperphenylalaninemia due to tetrahydrobiopterin deficiency inherited?

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

c.661C>T · rs779997983 · VCV802058

Pathogenic Multiple submitters

Classification

Pathogenic

ClinVar

Review

Multiple submitters ★★☆☆

ClinVar · 4 submitters

Consequence

nonsense (stop-gain)

predicted LoF

gnomAD v4.1

Rare

very rare (popmax 0.00167%, amr)

Conditions

dihydropteridine reductase deficiency

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	escapes	premature termination codon in the last exon (7 of 7) — the truncated protein is likely expressed. PVS1 input, not an applied code
Splicing
SpliceAI	—	not assessed · no allele here is in the release
Pangolin	Δ0.24	loss · gain 0.00 · not in the SpliceAI release · independent
Constraint at this position
Conservation	phyloP 6	GERP 0.49, phastCons 1
Overall
CADD	43.0	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 0.00167% Admixed American · 1/59,996 alleles

Filtering AF 0.000292% ClinGen BA1/BS1 input FAF95, joint · FAF99 0.000211%

Overall 0.00062% 10/1,613,970 alleles · very rare

Ancestry group	Frequency	1 in
Admixed Americangrpmax	0.00167%	59,996
Remaining individualsnot grpmax-eligible	0.0016%	62,488
European (non-Finnish)	0.000678%	147,502

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: QDPR
Protein: p.Arg221Ter
Coding: c.661C>T
MANE Select: NM_000320
dbSNP: rs779997983
Type: single nucleotide variant
Location: chr4:17487205 (GRCh38)
Gene constraint: LOEUF 0.984 · pLI <0.01 (gnomAD)
Structure: AlphaFold pLDDT 96.43 · 2 PDB
Residue 221: an α-helix

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

Disease context

dihydropteridine reductase deficiency — disease report on Sugi Atlas → Associated genes, phenotypes, clinical trials & treatments

For Hyperphenylalaninemia due to tetrahydrobiopterin deficiency (Orphanet):

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

Similar variants

QDPR p.Arg221Gln Uncertain significance ★★ ⚠ same residue
QDPR c.436+2552A>G Pathogenic ★★ same condition
QDPR c.545+1G>A Pathogenic ★★ same condition
QDPR c.546-1G>A Likely pathogenic ★★ same condition
QDPR p.His158Tyr Pathogenic/Likely pathogenic ★★ same condition
QDPR p.Phe212Ser Likely pathogenic ★★ same condition
QDPR p.Ser115Leu Pathogenic/Likely pathogenic ★★ same condition
QDPR p.Tyr150Cys 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/qdpr-p-arg221ter (accessed [today's date]).

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