rs281864883

Variant names:

• chr16-173502-G-A
• rs281864883
• NM_000517.6:c.331G>A

Variant summary

Our verdict is Likely pathogenic. The variant received 6 ACMG points: 6P and 0B. PM1 PM2 PP3_Moderate

The NM_000517.6(HBA2):​c.331G>A​(p.Ala111Thr) 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 1,458,448 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. No clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar. Another variant affecting the same amino acid position, but resulting in a different missense (i.e. A111V) has been classified as Uncertain significance.

• Frequency:
  • Genomes: not found (cov: 25)
  • Exomes 𝑓: 6.9e-7 (0 hom.)
• Consequence: HBA2 NM_000517.6 missense
• Clinical Significance: Not reported in ClinVar
• Conservation: PhyloP100: 3.54
• Publications: 0 publications found

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 Gene-Disease associations (from GenCC):

• alpha thalassemia spectrum

  Inheritance: AR Classification: DEFINITIVE, STRONG Submitted by: Labcorp Genetics (formerly Invitae), ClinGen
• erythrocytosis, familial, 7

  Inheritance: AD Classification: STRONG, LIMITED Submitted by: Genomics England PanelApp, Labcorp Genetics (formerly Invitae)
• hemoglobin M disease

  Inheritance: AD Classification: SUPPORTIVE Submitted by: Orphanet
• Hb Bart's hydrops fetalis

  Inheritance: AR Classification: SUPPORTIVE Submitted by: Orphanet
• hemoglobin H disease

  Inheritance: AR Classification: SUPPORTIVE Submitted by: Orphanet
• Heinz body anemia

  Inheritance: AD Classification: LIMITED Submitted by: Labcorp Genetics (formerly Invitae)
• methemoglobinemia, alpha type

  Inheritance: AD Classification: LIMITED Submitted by: ClinGen

ENSG00000294455 (HGNC:):

ACMG classification

Our verdict: Likely_pathogenic. The variant received 6 ACMG points.

• PM1: In a hotspot region, there are 5 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 5 benign, 11 uncertain in NM_000517.6
• PM2: Very rare variant in population databases, with high coverage
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.913

Variant Effect in Transcripts

ACMG analysis was done for transcript: NM_000517.6. You can select a different transcript below to see updated ACMG assignments.

RefSeq Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	HBA2	NM_000517.6	MANE Select	c.331G>A	p.Ala111Thr	missense	Exon 3 of 3	NP_000508.1

Ensembl Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	HBA2	ENST00000251595.11	TSL:1 MANE Select	c.331G>A	p.Ala111Thr	missense	Exon 3 of 3	ENSP00000251595.6
	HBA2	ENST00000482565.1	TSL:1	n.467G>A		non_coding_transcript_exon	Exon 2 of 2
	HBA2	ENST00000397806.1	TSL:2	c.235G>A	p.Ala79Thr	missense	Exon 3 of 3	ENSP00000380908.1

Frequencies

GnomAD3 genomes Cov.: 25

GnomAD4 exome AF: 6.86e-7 AC: 1 AN: 1458448 Hom.: 0 Cov.: 33 AF XY: 0.00000138 AC XY: 1 AN XY: 725328

African (AFR) AF: 0.0000315 AC: 1 AN: 31738

American (AMR) AF: 0.00 AC: 0 AN: 44672

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 26094

East Asian (EAS) AF: 0.00 AC: 0 AN: 39676

South Asian (SAS) AF: 0.00 AC: 0 AN: 85184

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53278

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 5712

European-Non Finnish (NFE) AF: 0.00 AC: 0 AN: 1111872

Other (OTH) AF: 0.00 AC: 0 AN: 60222

GnomAD4 genome Cov.: 25

ClinVar

Not reported in ClinVar

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.71
BayesDel_addAF	Pathogenic	0.31	D
BayesDel_noAF	Pathogenic	0.20
CADD	Benign	22
DANN	Uncertain	1.0
DEOGEN2	Benign	0.25	T
Eigen	Uncertain	0.40
Eigen_PC	Uncertain	0.23
FATHMM_MKL	Uncertain	0.88	D
M_CAP	Pathogenic	0.83	D
MetaRNN	Pathogenic	0.91	D
MetaSVM	Pathogenic	0.97	D
PhyloP100		3.5
PrimateAI	Uncertain	0.58	T
PROVEAN	Uncertain	-3.6	D
REVEL	Pathogenic	0.83
Sift	Pathogenic	0.0	D
Sift4G	Pathogenic	0.0010	D
Vest4		0.52
MutPred		0.76		Gain of glycosylation at A111 (P = 0.1656)
MVP		1.0
MPC		2.4
ClinPred		1.0	D
GERP RS		3.3
RBP_binding_hub_radar		0.0
RBP_regulation_power_radar		1.9
gMVP		0.77

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

Other links and lift over

dbSNP: rs281864883; hg19: chr16-223501;