chr16-173302-G-T

Position:

• chr16-173302-G-T

Variant summary

Our verdict is Uncertain significance. Variant got 3 ACMG points: 4P and 1B. PP3_Strong BP6

The NM_000517.6(HBA2):​c.273G>T​(p.Lys91Asn) variant causes a missense change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.00000859 in 1,396,262 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Conflicting classifications of pathogenicity (no stars). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. K91M) has been classified as Likely benign.

• Frequency:
  • Genomes: not found (cov: 24)
  • Exomes 𝑓: 0.0000086 (0 hom.)
• Consequence: HBA2 NM_000517.6 missense
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications U:2 B:1
• Conservation: PhyloP100: -0.455

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]

HBA2 (HGNC:):

ACMG classification

Verdict is Uncertain_significance. Variant got 3 ACMG points.

• PP3: MetaRNN computational evidence supports a deleterious effect, 0.965
• BP6: Variant 16-173302-G-T is Benign according to our data. Variant chr16-173302-G-T is described in ClinVar as [Conflicting_classifications_of_pathogenicity]. Clinvar id is 2428590.We mark this variant Likely_benign, oryginal submissions are: {Likely_benign=1, Uncertain_significance=1}.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
HBA2	NM_000517.6	c.273G>T	p.Lys91Asn	missense_variant	2/3	ENST00000251595.11	NP_000508.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
HBA2	ENST00000251595.11	c.273G>T	p.Lys91Asn	missense_variant	2/3	1	NM_000517.6	ENSP00000251595.6
HBA2	ENST00000484216.1	c.240G>T	p.Lys80Asn	missense_variant	2/2	1		ENSP00000495899.1
HBA2	ENST00000482565.1	n.409G>T		non_coding_transcript_exon_variant	1/2	1
HBA2	ENST00000397806.1	c.177G>T	p.Lys59Asn	missense_variant	2/3	2		ENSP00000380908.1

Frequencies

GnomAD3 genomes Cov.: 24

GnomAD4 exome AF: 0.00000859 AC: 12 AN: 1396262 Hom.: 0 Cov.: 27 AF XY: 0.0000101 AC XY: 7 AN XY: 693700

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: 0.0000111

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 24

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Uncertain:2 Benign:1

Revision: criteria provided, conflicting classifications

Submissions by phenotype

not provided Uncertain:1 Benign:1

Uncertain significance, criteria provided, single submitter	clinical testing	Quest Diagnostics Nichols Institute San Juan Capistrano	Feb 13, 2023	The HBA2 c.273G>T (p.Lys91Asn) variant is described to have normal oxygen affinity and relative stability, with quantities in heterozygotes at 24-25%. It has not been reported in large, multi-ethnic general populations (http://gnomad.broadinstitute.org). In heterozygotes, the variant is clinically silent with hematological parameters within normal limits and normal peripheral blood morphology (PMIDs: 7803274 (1994), 740406 (1978), 5452727 (1970)). Analysis of this variant using bioinformatics tools for the prediction of the effect of amino acid changes on protein structure and function yielded conflicting predictions that this variant is deleterious or benign. Based on the available information, we are unable to determine the clinical significance of this variant. -
Likely benign, criteria provided, single submitter	clinical testing	ARUP Laboratories, Molecular Genetics and Genomics, ARUP Laboratories	Sep 22, 2022	- -

HBA2-related disorder Uncertain:1

Uncertain significance, no assertion criteria provided

clinical testing

PreventionGenetics, part of Exact Sciences

Mar 07, 2024

The HBA2 c.273G>T variant is predicted to result in the amino acid substitution p.Lys91Asn. This variant is also known as Hb J-Broussais or p.Lys90Asn using legacy nomenclature. This variant does not affect the protein stability or the affinity with oxygen. Individuals carrying this variant were generally considered to be clinically normal (Braconnier et al. 1975. PubMed ID: 128734; Molchanova et al. 1994. PubMed ID: 7803274; Durou et al. 1996. PubMed ID: 9092311). This variant has not been reported in a large population database, indicating this variant is rare. At this time, the clinical significance of this variant is uncertain due to the absence of conclusive functional and genetic evidence. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Uncertain	0.15	D
BayesDel_noAF	Uncertain	-0.020
CADD	Benign	18
DANN	Uncertain	0.98
DEOGEN2	Benign	0.018	.;T
Eigen	Benign	-0.51
Eigen_PC	Benign	-0.50
FATHMM_MKL	Benign	0.52	D
M_CAP	Pathogenic	0.44	D
MetaRNN	Pathogenic	0.97	D;D
MetaSVM	Uncertain	0.16	D
PrimateAI	Uncertain	0.65	T
PROVEAN	Benign	-1.5	N;N
REVEL	Uncertain	0.52
Sift	Pathogenic	0.0	D;D
Sift4G	Benign	0.31	T;T
Vest4		0.59
MutPred		0.97		Loss of ubiquitination at K91 (P = 0.0167);.;
MVP		1.0
MPC		1.5
ClinPred		0.86	D
GERP RS		2.0
gMVP		0.98

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: rs281860615; hg19: chr16-223301;