16-173515-C-T

Variant names:

• chr16-173515-C-T
• rs267607269
• NM_000517.6:c.344C>T

Variant summary

Our verdict is Uncertain significance. Variant got 1 ACMG points: 2P and 1B. PM2 BP6

The NM_000517.6(HBA2):​c.344C>T​(p.Pro115Leu) variant causes a missense change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.000000686 in 1,458,650 control chromosomes in the GnomAD database, with no homozygous occurrence. Variant has been reported in ClinVar as Conflicting classifications of pathogenicity (no stars). Another nucleotide change resulting in the same amino acid substitution has been previously reported as Likely benign in UniProt. Another variant affecting the same amino acid position, but resulting in a different missense (i.e. P115R) has been classified as Likely benign.

• Frequency:
  • Genomes: not found (cov: 25)
  • Exomes 𝑓: 6.9e-7 (0 hom.)
• Consequence: HBA2 NM_000517.6 missense
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications U:1 B:1
• Conservation: PhyloP100: 0.262

Genes affected

HBA2 (HGNC:4824): (hemoglobin subunit alpha 2) The human alpha globin gene cluster located on chromosome 16 spans about 30 kb and includes seven loci: 5'- zeta - pseudozeta - mu - pseudoalpha-1 - alpha-2 - alpha-1 - theta - 3'. The alpha-2 (HBA2) and alpha-1 (HBA1) coding sequences are identical. These genes differ slightly over the 5' untranslated regions and the introns, but they differ significantly over the 3' untranslated regions. Two alpha chains plus two beta chains constitute HbA, which in normal adult life comprises about 97% of the total hemoglobin; alpha chains combine with delta chains to constitute HbA-2, which with HbF (fetal hemoglobin) makes up the remaining 3% of adult hemoglobin. Alpha thalassemias result from deletions of each of the alpha genes as well as deletions of both HBA2 and HBA1; some nondeletion alpha thalassemias have also been reported. [provided by RefSeq, Jul 2008]

ENSG00000290038 (HGNC:):

ACMG classification

Verdict is Uncertain_significance. Variant got 1 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• BP6: Variant 16-173515-C-T is Benign according to our data. Variant chr16-173515-C-T is described in ClinVar as [Conflicting_classifications_of_pathogenicity]. Clinvar id is 439115.We mark this variant Likely_benign, oryginal submissions are: {Likely_benign=1, Uncertain_significance=1}.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
HBA2	NM_000517.6	c.344C>T	p.Pro115Leu	missense_variant	Exon 3 of 3	ENST00000251595.11	NP_000508.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
HBA2	ENST00000251595.11	c.344C>T	p.Pro115Leu	missense_variant	Exon 3 of 3	1	NM_000517.6	ENSP00000251595.6

Frequencies

GnomAD3 genomes Cov.: 25

GnomAD4 exome AF: 6.86e-7 AC: 1 AN: 1458650 Hom.: 0 Cov.: 33 AF XY: 0.00000138 AC XY: 1 AN XY: 725410

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.00

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.00

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 8.99e-7

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 25

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Uncertain:1 Benign:1

Revision: criteria provided, conflicting classifications

Submissions by phenotype

not provided Uncertain:1

Feb 22, 2024

Quest Diagnostics Nichols Institute San Juan Capistrano

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The HBA2 c.344C>T (p.Pro115Leu) variant (also known as Hb Noukchott) has been reported in the published literature in two unrelated asymptomatic Dutch families (PMID: 29405838 (2018)). It was also reported to increase hydrophobicity, however, binding and stability were unaffected (PMID 2790052 (1989)). This variant has not been reported in large, multi-ethnic general populations (Genome Aggregation Database, http://gnomad.broadinstitute.org). Analysis of this variant using bioinformatics tools for the prediction of the effect of amino acid changes on protein structure and function yielded predictions that this variant is benign. Based on the available information, we are unable to determine the clinical significance of this variant. -

not specified Benign:1

Oct 30, 2018

ARUP Laboratories, Molecular Genetics and Genomics, ARUP Laboratories

Significance: Likely benign

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The HBA2 c.344C>T; Pro114Leu variant (rs267607269), also known as Hb Nouakchott, has been reported in the heterozygous state in asymptomatic individuals with normal hematological parameters (see link to HbVar and references therein, Pondman 2018). It contains an entry in ClinVar (Variation ID: 439115) and is absent from general population databases (1000 Genomes Project, Exome Variant Server, and Genome Aggregation Database), indicating it is not a common polymorphism. The proline at codon 114 is moderately conserved, but computational algorithms (PolyPhen-2: benign, SIFT: damaging) are inconclusive on the effect of this variant on protein structure and/or function. Based on available information, the Hb Nouakchott variant is considered likely benign. REFERENCES Link to HbVar: http://globin.bx.psu.edu/cgi-bin/hbvar/query_vars3?mode=output&display_format=page&i=177 Pondman K et al. Hb Nouakchott [a114(GH2)Pro?Leu; HBA1: c.344C>T], A Second and Third Case Described in Two Unrelated Dutch Families. Hemoglobin. 2018 Jan;42(1):51-53. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.18	D
BayesDel_noAF	Uncertain	0.020
CADD	Benign	18
DANN	Benign	0.97
DEOGEN2	Benign	0.28	.;T
Eigen	Benign	-0.58
Eigen_PC	Benign	-0.71
FATHMM_MKL	Benign	0.23	N
M_CAP	Pathogenic	0.60	D
MetaRNN	Uncertain	0.56	D;D
MetaSVM	Uncertain	0.38	D
PrimateAI	Uncertain	0.50	T
PROVEAN	Pathogenic	-7.4	D;D
REVEL	Uncertain	0.42
Sift	Pathogenic	0.0	D;D
Sift4G	Uncertain	0.0080	D;D
Vest4		0.26
MutPred		0.52		Gain of catalytic residue at P115 (P = 0.0214);.;
MVP		0.99
MPC		1.3
ClinPred		1.0	D
GERP RS		1.9
RBP_binding_hub_radar		0.0
RBP_regulation_power_radar		1.3
gMVP		0.89

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.0		Details are displayed if max score is > 0.2

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

Publications

LitVar

Other links and lift over

dbSNP: rs267607269; hg19: chr16-223514;