chr16-172914-T-G

Position:

• chr16-172914-T-G

Variant summary

Our verdict is Pathogenic. Variant got 10 ACMG points: 10P and 0B. PVS1 PP5_Moderate

The NM_000517.6(HBA2):​c.2T>G​(p.Met1?) variant causes a start lost change involving the alteration of a non-conserved nucleotide. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Likely pathogenic (★).

• Frequency: Genomes: not found (cov: 0)
• Consequence: HBA2 NM_000517.6 start_lost
• Clinical Significance: Likely pathogenic criteria provided, single submitter P:1
• Conservation: PhyloP100: 2.03

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 Pathogenic. Variant got 10 ACMG points.

• PVS1: Start lost variant, no new inframe start found.
• PP5: Variant 16-172914-T-G is Pathogenic according to our data. Variant chr16-172914-T-G is described in ClinVar as [Likely_pathogenic]. Clinvar id is 3075919.Status of the report is criteria_provided_single_submitter, 1 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
HBA2	NM_000517.6	c.2T>G	p.Met1?	start_lost	1/3	ENST00000251595.11	NP_000508.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
HBA2	ENST00000251595.11	c.2T>G	p.Met1?	start_lost	1/3	1	NM_000517.6	ENSP00000251595.6
HBA2	ENST00000482565.1	n.21T>G		non_coding_transcript_exon_variant	1/2	1
HBA2	ENST00000397806	c.-46T>G		5_prime_UTR_variant	1/3	2		ENSP00000380908.1
HBA2	ENST00000484216.1	c.-32T>G		upstream_gene_variant		1		ENSP00000495899.1

Frequencies

GnomAD3 genomes Cov.: 0

GnomAD4 exome Cov.: 0

GnomAD4 genome Cov.: 0

ClinVar

Significance: Likely pathogenic

Submissions summary: Pathogenic:1

Revision: criteria provided, single submitter

Submissions by phenotype

alpha Thalassemia Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Laboratory for Molecular Medicine, Mass General Brigham Personalized Medicine

Feb 02, 2023

The p.Met1? (c.2T>G) in HBA2 has been previously reported in 1 individual with alpha thalessemia (Hadavi 2007 PMID 17606454). It was absent in large population studies. This variant affects the translation initiation start codon (ATG) and is therefore predicted to disrupt translation although a variety of outcomes (no protein synthesis or the activation of an upstream translation initiation codon) are possible. Other Met1? variants (c.1A>G, c.2T>C) have been reported in individuals with alpha thalessemia, and are classified as pathogenic by ClinVar submitters. In summary, although additional studies are required to fully establish its clinical significance, this variant meets criteria to be classified as likely pathogenic for autosomal recessive alpha thalessemia. ACMG/AMP Criteria applied: PVS1_Moderate, PM5, PM2_Supporting, PP4. (This variant did not meet the variant calling quality criteria, and was included because it has been previously reported as a clinically significant variant.) -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.60	D
BayesDel_noAF	Pathogenic	0.43
CADD	Uncertain	24
DANN	Benign	0.97
Eigen	Uncertain	0.31
Eigen_PC	Benign	0.22
FATHMM_MKL	Uncertain	0.94	D
M_CAP	Pathogenic	0.98	D
MetaRNN	Pathogenic	0.99	D
MetaSVM	Pathogenic	0.81	D
PROVEAN	Uncertain	-3.6	D
REVEL	Pathogenic	0.89
Sift	Pathogenic	0.0	D
Sift4G	Pathogenic	0.0	D
Vest4		0.94
MutPred		0.99		Gain of MoRF binding (P = 0.002);
MVP		1.0
ClinPred		0.99	D
GERP RS		2.6
gMVP		0.79

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: rs111033603; hg19: chr16-222913;