rs281864863

Variant names:

• chr16-173271-T-G
• rs281864863
• NM_000517.6:c.242T>G

Variant summary

Our verdict is Pathogenic. The variant received 10 ACMG points: 10P and 0B. PM2 PM5 PP3_Strong PP5_Moderate

The NM_000517.6(HBA2):​c.242T>G​(p.Leu81Arg) variant causes a missense change involving the alteration of a conserved nucleotide. The variant allele was found at a frequency of 0.000000733 in 1,364,622 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 Likely pathogenic (★). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. L81V) has been classified as Uncertain significance.

• Frequency:
  • Genomes: not found (cov: 23)
  • Exomes 𝑓: 7.3e-7 (0 hom.)
• Consequence: HBA2 NM_000517.6 missense
• Clinical Significance: Likely pathogenic criteria provided, single submitter P:1
• Conservation: PhyloP100: 7.40
• 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: Pathogenic. The variant received 10 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PM5: Other missense variant is known to change same aminoacid residue: Variant chr16-173271-T-C is described in ClinVar as Likely_pathogenic. ClinVar VariationId is 3766515.Status of the report is criteria_provided_single_submitter, 1 stars.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.995
• PP5: Variant 16-173271-T-G is Pathogenic according to our data. Variant chr16-173271-T-G is described in ClinVar as Likely_pathogenic. ClinVar VariationId is 993412.Status of the report is criteria_provided_single_submitter, 1 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
HBA2	NM_000517.6	c.242T>G	p.Leu81Arg	missense_variant	Exon 2 of 3	ENST00000251595.11	NP_000508.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
HBA2	ENST00000251595.11	c.242T>G	p.Leu81Arg	missense_variant	Exon 2 of 3	1	NM_000517.6	ENSP00000251595.6

Frequencies

GnomAD3 genomes Cov.: 23

GnomAD4 exome AF: 7.33e-7 AC: 1 AN: 1364622 Hom.: 0 Cov.: 26 AF XY: 0.00 AC XY: 0 AN XY: 677298

⚠️ The allele balance in gnomAD version 4 Exomes is significantly skewed from the expected value of 0.5.

African (AFR) AF: 0.00 AC: 0 AN: 27218

American (AMR) AF: 0.00 AC: 0 AN: 38536

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 25016

East Asian (EAS) AF: 0.00 AC: 0 AN: 37176

South Asian (SAS) AF: 0.00 AC: 0 AN: 78840

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 36112

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 3938

European-Non Finnish (NFE) AF: 9.42e-7 AC: 1 AN: 1061028

Other (OTH) AF: 0.00 AC: 0 AN: 56758

⚠️ The allele balance in gnomAD4 Exomes is highly skewed from 0.5 (p-value = 0), which strongly suggests a high chance of mosaicism in these individuals.

GnomAD4 genome Cov.: 23

ClinVar

Significance: Likely pathogenic

Submissions summary: Pathogenic:1

Revision: criteria provided, single submitter

Submissions by phenotype

not provided Pathogenic:1

Dec 16, 2019

ARUP Laboratories, Molecular Genetics and Genomics, ARUP Laboratories

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The Hb Ann Arbor variant (HBA2: c.242T>G; p.Leu81Arg, also known as Leu80Arg when numbered from the mature protein rs281864863) is reported in the literature in two brothers affected with hemolytic microcytic anemia (Adams 1972, Adams 1974, HbVar database). Both affected brothers carried Hb Ann Arbor in the heterozygous state and were presumed to carry an additional undetermined alpha-thalassemia allele in trans, although this second allele was not determined (Adams 1974). This variant is absent from general population databases (Exome Variant Server, Genome Aggregation Database), indicating it is not a common polymorphism. The affected brothers with Hb Ann Arbor exhibited 10-15% abnormal hemoglobin, while other family members that carried Hb Ann Arbor exhibited 2-5% abnormal hemoglobin (Adams 1974). The proportions of abnormal hemoglobin in heterozygous carriers, heat stability assays, and functional assays of protein synthesis all suggest Hb Ann Arbor is unstable and rapidly degraded (Adams 1972, Adams 1974). Based on available information, this variant is considered to be likely pathogenic. References: Link to Hb Ann Arbor in HbVar database: http://globin.bx.psu.edu/cgi-bin/hbvar/query_vars3?mode=output&display_format=page&i=123 Adams JG 3rd et al. Biosynthesis of hemoglobin Ann Arbor: evidence for catabolic and feedback regulation. Science. 1972 Jun 30;176(4042):1427-9. Adams JG 3rd. Hemoglobin Ann Arbor: disturbance in the coordinated biosynthesis of globin chains? Ann N Y Acad Sci. 1974 Nov 29;241(0):232-41. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.97
BayesDel_addAF	Pathogenic	0.52	D
BayesDel_noAF	Pathogenic	0.52
CADD	Uncertain	23
DANN	Uncertain	1.0
DEOGEN2	Benign	0.18	.;T
Eigen	Uncertain	0.57
Eigen_PC	Uncertain	0.38
FATHMM_MKL	Pathogenic	0.97	D
M_CAP	Pathogenic	0.88	D
MetaRNN	Pathogenic	1.0	D;D
MetaSVM	Pathogenic	1.1	D
PhyloP100		7.4
PrimateAI	Uncertain	0.67	T
PROVEAN	Pathogenic	-5.7	D;D
REVEL	Pathogenic	0.88
Sift	Pathogenic	0.0	D;D
Sift4G	Pathogenic	0.0	D;D
Vest4		0.95
MutPred		0.91		Gain of methylation at L81 (P = 0.0199);.;
MVP		1.0
MPC		3.0
ClinPred		1.0	D
GERP RS		4.2
PromoterAI		-0.022	Neutral
gMVP		0.99

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: rs281864863; hg19: chr16-223270;