16-172908-CCA-C

Position:

• chr16-172908-CCA-C

Variant summary

Our verdict is Uncertain significance. Variant got 0 ACMG points: 0P and 0B.

The NM_000517.6(HBA2):​c.-3_-2del variant causes a 5 prime UTR change involving the alteration of a non-conserved nucleotide. Variant has been reported in ClinVar as Uncertain significance (★).

• Frequency:
  • Genomes: not found (cov: 0)
  • Exomes 𝑓: 0.0000039 (0 hom.)
  • Failed GnomAD Quality Control
• Consequence: HBA2 NM_000517.6 5_prime_UTR
• Clinical Significance: Uncertain significance criteria provided, single submitter U:1
• Conservation: PhyloP100: 2.52

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]

ACMG classification

Verdict is Uncertain_significance. Variant got 0 ACMG points.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
HBA2	NM_000517.6	c.-3_-2del		5_prime_UTR_variant	1/3	ENST00000251595.11

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
HBA2	ENST00000251595.11	c.-3_-2del		5_prime_UTR_variant	1/3	1	NM_000517.6	P1
HBA2	ENST00000482565.1	n.17_18del		non_coding_transcript_exon_variant	1/2	1
HBA2	ENST00000397806.1	c.-50_-49del		5_prime_UTR_variant	1/3	2
HBA2	ENST00000484216.1			upstream_gene_variant		1

Frequencies

GnomAD3 genomes Cov.: 0

GnomAD4 exome Data not reliable, filtered out with message: AS_VQSR AF: 0.00000390 AC: 1 AN: 256564 Hom.: 0 AF XY: 0.00 AC XY: 0 AN XY: 136934

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: 0.00000676

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 0

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:1

Revision: criteria provided, single submitter

Submissions by phenotype

not specified Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Women's Health and Genetics/Laboratory Corporation of America, LabCorp

Oct 26, 2023

Variant summary: HBA2 c.-3_-2delAC is located in the untranslated mRNA region upstream of the initiation codon. Consensus agreement among computation tools predict no significant impact on normal splicing. At least one study showed this variant did not affect mRNA splicing (Morle_1985). The variant was absent in 53060 control chromosomes (gnomAD). c.-3_-2delAC has been reported in the literature in one individual affected with Alpha Thalassemia (Morle_1985). These data indicate that the variant may be associated with disease. At least one publication reports experimental evidence evaluating an impact on protein function and this variant leads to a 30-45% reduction in translation efficiency in vitro (Morle_1986). The following publications have been ascertained in the context of this evaluation (PMID: 4006915, 3703675). No submitters have cited clinical-significance assessments for this variant to ClinVar after 2014. Based on the evidence outlined above, the variant was classified as VUS-possibly pathogenic. -

Computational scores

Source: dbNSFP v4.3

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: rs1902035067; hg19: chr16-222907;