chr16-176717-AT-A

Position:

• chr16-176717-AT-A

Variant summary

Our verdict is Pathogenic. Variant got 14 ACMG points: 14P and 0B. PVS1 PS1_Moderate PM2 PP5_Moderate

The NM_000558.5(HBA1):​c.2del​(p.Met1?) variant causes a frameshift, start lost change involving the alteration of a non-conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. Variant has been reported in ClinVar as Likely pathogenic (★).

• Frequency:
  • Genomes: not found (cov: 28)
  • Exomes 𝑓: 6.9e-7 (0 hom.)
  • Failed GnomAD Quality Control
• Consequence: HBA1 NM_000558.5 frameshift, start_lost
• Clinical Significance: Likely pathogenic criteria provided, single submitter P:1
• Conservation: PhyloP100: 2.48

Genes affected

HBA1 (HGNC:4823): (hemoglobin subunit alpha 1) 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]

ACMG classification

Verdict is Pathogenic. Variant got 14 ACMG points.

• PVS1: Loss of function variant, product does not undergo nonsense mediated mRNA decay. Variant located near the start codon (<100nt), not predicted to undergo nonsense mediated mRNA decay. There are 33 pathogenic variants in the truncated region.
• PS1: Another start lost variant in NM_000558.5 (HBA1) was described as [Likely_pathogenic] in ClinVar as 2573442
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 16-176717-AT-A is Pathogenic according to our data. Variant chr16-176717-AT-A is described in ClinVar as [Likely_pathogenic]. Clinvar id is 1162201.Status of the report is criteria_provided_single_submitter, 1 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
HBA1	NM_000558.5	c.2del	p.Met1?	frameshift_variant, start_lost	1/3	ENST00000320868.9

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
HBA1	ENST00000320868.9	c.2del	p.Met1?	frameshift_variant, start_lost	1/3	1	NM_000558.5	P1
HBA1	ENST00000472694.1	n.21del		non_coding_transcript_exon_variant	1/2	1
HBA1	ENST00000397797.1	c.-46del		5_prime_UTR_variant	1/3	2
HBA1	ENST00000487791.1			upstream_gene_variant		1

Frequencies

GnomAD3 genomes Cov.: 28

GnomAD4 exome Data not reliable, filtered out with message: AS_VQSR AF: 6.88e-7 AC: 1 AN: 1454218 Hom.: 0 Cov.: 31 AF XY: 0.00000138 AC XY: 1 AN XY: 722990

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.00

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.0000254

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.00

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 28

Bravo AF: 0.00000756

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

NxGen MDx

Dec 30, 2019

This null variant (c.2del) is predicted to result in start loss in a gene where loss-of-function is a known mechanism of disease (PVS1). This variant is not found in gnomAD databases (PM2) and is not referenced in the literature. An alternate variant that results in the loss of the initiator methionine, c.2T>A, p.Met1Lys, has been described by Waye et al. (PMID: 27821014) and Shang et al. (PMID 28865746) in association with alpha thalassemia. We interpret c.2del to be likely pathogenic. -

Computational scores

Source: dbNSFP v4.3

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.010		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: rs1298047912; hg19: chr16-226716;