16-176967-C-T

Variant names:

• chr16-176967-C-T
• rs33978134
• NM_000558.5:c.134C>T

Variant summary

Our verdict is Uncertain significance. The variant received 4 ACMG points: 4P and 0B. PM2 PP5_Moderate

The NM_000558.5(HBA1):​c.134C>T​(p.Pro45Leu) variant causes a missense change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.000000955 in 1,046,752 control chromosomes in the GnomAD database, with no homozygous occurrence. 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. P45R) has been classified as Uncertain significance.

• Frequency:
  • Genomes: not found (cov: 30)
  • Exomes 𝑓: 9.6e-7 (0 hom.)
• Consequence: HBA1 NM_000558.5 missense
• Clinical Significance: Likely pathogenic criteria provided, single submitter P:2 O:1
• Conservation: PhyloP100: 0.683
• Publications: 3 publications found

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]

HBA1 Gene-Disease associations (from GenCC):

• alpha thalassemia spectrum

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

  Inheritance: AD Classification: STRONG Submitted by: Genomics England PanelApp
• 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
• methemoglobinemia, alpha type

  Inheritance: AD Classification: LIMITED Submitted by: ClinGen
• Heinz body anemia

  Inheritance: AR Classification: LIMITED Submitted by: Labcorp Genetics (formerly Invitae)

ENSG00000294436 (HGNC:):

ACMG classification

Our verdict: Uncertain_significance. The variant received 4 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 16-176967-C-T is Pathogenic according to our data. Variant chr16-176967-C-T is described in ClinVar as Likely_pathogenic. ClinVar VariationId is 15783.Status of the report is criteria_provided_single_submitter, 1 stars.

Variant Effect in Transcripts

ACMG analysis was done for transcript: NM_000558.5. 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
	HBA1	NM_000558.5	MANE Select	c.134C>T	p.Pro45Leu	missense	Exon 2 of 3	NP_000549.1

Ensembl Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	HBA1	ENST00000320868.9	TSL:1 MANE Select	c.134C>T	p.Pro45Leu	missense	Exon 2 of 3	ENSP00000322421.5
	HBA1	ENST00000472694.1	TSL:1	n.270C>T		non_coding_transcript_exon	Exon 1 of 2
	HBA1	ENST00000487791.1	TSL:1	n.103C>T		non_coding_transcript_exon	Exon 2 of 2

Frequencies

GnomAD3 genomes Cov.: 30

GnomAD4 exome AF: 9.55e-7 AC: 1 AN: 1046752 Hom.: 0 Cov.: 14 AF XY: 0.00000188 AC XY: 1 AN XY: 532460

African (AFR) AF: 0.00 AC: 0 AN: 24978

American (AMR) AF: 0.00 AC: 0 AN: 37812

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 23034

East Asian (EAS) AF: 0.00 AC: 0 AN: 35304

South Asian (SAS) AF: 0.00 AC: 0 AN: 75510

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 36722

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 3400

European-Non Finnish (NFE) AF: 0.00000131 AC: 1 AN: 763540

Other (OTH) AF: 0.00 AC: 0 AN: 46452

GnomAD4 genome Cov.: 30

ClinVar

Significance: Likely pathogenic

Submissions summary: Pathogenic:2 Other:1

Revision: criteria provided, single submitter

Submissions by phenotype

not provided Pathogenic:1

Dec 16, 2021

ARUP Laboratories, Molecular Genetics and Genomics, ARUP Laboratories

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The Hb Milledgeville variant (HBA1: c.134C>T; p.Pro45Leu, also known as Pro44Leu when numbered from the mature protein, rs33978134) has been found heterozygous in multiple individuals with mild erythrocytosis (see link to HbVar and references therein). This variant has been reported to have increased oxygen affinity with reduced cooperativity. This variant is absent from the Genome Aggregation Database, indicating it is not a common polymorphism. The proline at codon 45 is highly conserved, and computational analyses are uncertain whether this variant is neutral or deleterious (REVEL: 0.544). Based on available information, this variant is considered to be likely pathogenic. References: Link to HbVar for Hb Milledgeville: https://globin.bx.psu.edu/cgi-bin/hbvar/query_vars3?mode=output&display_format=page&i=57&.cgifields=histD

Erythrocytosis, familial, 7 Pathogenic:1

Dec 16, 1980

OMIM

Significance: Pathogenic

Review Status: no assertion criteria provided

Collection Method: literature only

HEMOGLOBIN MILLEDGEVILLE Other:1

Nov 01, 2019

OMIM

Significance: other

Review Status: no assertion criteria provided

Collection Method: literature only

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Uncertain	0.50
BayesDel_addAF	Pathogenic	0.18	D
BayesDel_noAF	Uncertain	0.030
CADD	Benign	23
DANN	Uncertain	1.0
DEOGEN2	Benign	0.29	T
Eigen	Benign	-0.16
Eigen_PC	Benign	-0.22
FATHMM_MKL	Benign	0.48	N
LIST_S2	Benign	0.85	T
M_CAP	Pathogenic	0.57	D
MetaRNN	Uncertain	0.69	D
MetaSVM	Uncertain	0.54	D
PhyloP100		0.68
PrimateAI	Benign	0.44	T
PROVEAN	Pathogenic	-7.6	D
REVEL	Uncertain	0.54
Sift	Uncertain	0.0070	D
Sift4G	Benign	0.076	T
Vest4		0.47
MutPred		0.29		Loss of methylation at K41 (P = 0.0812)
MVP		0.98
ClinPred		0.97	D
GERP RS		2.3
PromoterAI		0.23	Neutral
Varity_R		0.51
gMVP		0.82
Mutation Taster		=9/91	disease causing (ClinVar)

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

Other links and lift over

dbSNP: rs33978134; hg19: chr16-226966;