rs33918778

Positions:

• chr11-5226769-C-A
• chr11-5226769-C-G

Variant summary

Our verdict is Likely pathogenic. Variant got 8 ACMG points: 8P and 0B. PM1 PM2 PP3_Strong

The NM_000518.5(HBB):​c.123G>T​(p.Arg41Ser) variant causes a missense change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.00000657 in 152,142 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 Uncertain significance (★★). Another nucleotide change resulting in same amino acid change has been previously reported as Uncertain significancein ClinVar. Another variant affecting the same amino acid position, but resulting in a different missense (i.e. R41K) has been classified as Likely benign.

• Frequency: Genomes: 𝑓 0.0000066 (0 hom., cov: 32)
• Consequence: HBB NM_000518.5 missense
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:4
• Conservation: PhyloP100: 1.96

Genes affected

HBB (HGNC:4827): (hemoglobin subunit beta) The alpha (HBA) and beta (HBB) loci determine the structure of the 2 types of polypeptide chains in adult hemoglobin, Hb A. The normal adult hemoglobin tetramer consists of two alpha chains and two beta chains. Mutant beta globin causes sickle cell anemia. Absence of beta chain causes beta-zero-thalassemia. Reduced amounts of detectable beta globin causes beta-plus-thalassemia. The order of the genes in the beta-globin cluster is 5'-epsilon -- gamma-G -- gamma-A -- delta -- beta--3'. [provided by RefSeq, Jul 2008]

ACMG classification

Verdict is Likely_pathogenic. Variant got 8 ACMG points.

• PM1: In a hotspot region, there are 6 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 3 benign, 16 uncertain in NM_000518.5
• PM2: Very rare variant in population databases, with high coverage
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.968

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
HBB	NM_000518.5	c.123G>T	p.Arg41Ser	missense_variant	2/3	ENST00000335295.4

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
HBB	ENST00000335295.4	c.123G>T	p.Arg41Ser	missense_variant	2/3	1	NM_000518.5	P1

Frequencies

GnomAD3 genomes AF: 0.00000657 AC: 1 AN: 152142 Hom.: 0 Cov.: 32

Gnomad AFR AF: 0.00

Gnomad AMI AF: 0.00

Gnomad AMR AF: 0.0000655

Gnomad ASJ AF: 0.00

Gnomad EAS AF: 0.00

Gnomad SAS AF: 0.00

Gnomad FIN AF: 0.00

Gnomad MID AF: 0.00

Gnomad NFE AF: 0.00

Gnomad OTH AF: 0.00

GnomAD4 exome Cov.: 36

GnomAD4 genome AF: 0.00000657 AC: 1 AN: 152142 Hom.: 0 Cov.: 32 AF XY: 0.00 AC XY: 0 AN XY: 74320

Gnomad4 AFR AF: 0.00

Gnomad4 AMR AF: 0.0000655

Gnomad4 ASJ AF: 0.00

Gnomad4 EAS AF: 0.00

Gnomad4 SAS AF: 0.00

Gnomad4 FIN AF: 0.00

Gnomad4 NFE AF: 0.00

Gnomad4 OTH AF: 0.00

Bravo AF: 0.0000113

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:4

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

not provided Uncertain:2

Uncertain significance, criteria provided, single submitter	clinical testing	ARUP Laboratories, Molecular Genetics and Genomics, ARUP Laboratories	Nov 20, 2023	The Hb Austin variant (HBB: c.123G>T; p.Arg41Ser, also known as Arg40Ser when numbered from the mature protein, rs33918778, HbVar ID: 311) is reported in the literature in the heterozygous state in multiple individuals of Mexican ancestry with no clinical symptoms (HbVar and references therein, Racsa 2014, Moo-Penn 1977). However, the phenotype of this variant in the presence of other alpha globin variants is unknown. Functional characterization indicate that the variant hemoglobin has normal Bohr effect, increased oxygen affinity, reduced cooperativity, and found to dissociate into oxyHb dimers (HbVar and references therein). The c.123G>T variant is reported in ClinVar (Variation ID: 439134). It is absent from the Genome Aggregation Database (v2.1.1), indicating it is not a common polymorphism. Computational analyses predict that this variant is deleterious (REVEL: 0.9). Due to the limited information regarding this variant, its clinical significance is uncertain at this time. References: Link to HbVar database: https://globin.bx.psu.edu/hbvar/menu.html Racsa LD et al. Beta-Globin gene sequencing of hemoglobin Austin revises the historically reported electrophoretic migration pattern. Arch Pathol Lab Med. 2014 Jun;138(6):819-22. PMID: 24878022. Moo-Penn WF et al. Hemoglobins Austin and Waco: two hemoglobins with substitutions in the alpha 1 beta 2 contact region. Arch Biochem Biophys. 1977 Feb;179(1):86-94. doi: 10.1016/0003-9861(77)90089-3. PMID: 14597. -
Uncertain significance, criteria provided, single submitter	clinical testing	Quest Diagnostics Nichols Institute San Juan Capistrano	Feb 09, 2020	- -

beta Thalassemia Uncertain:1

Uncertain significance, no assertion criteria provided

clinical testing

Natera, Inc.

Sep 16, 2020

- -

alpha Thalassemia;C0002895:Hb SS disease;C0019025:Hereditary persistence of fetal hemoglobin;C0700299:Heinz body anemia;C1840779:METHEMOGLOBINEMIA, BETA TYPE;C1858990:Dominant beta-thalassemia;C1970028:Malaria, susceptibility to;C4693822:Erythrocytosis, familial, 6;CN322236:Beta-thalassemia HBB/LCRB Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Fulgent Genetics, Fulgent Genetics

Dec 28, 2021

- -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.99
BayesDel_addAF	Pathogenic	0.47	D
BayesDel_noAF	Pathogenic	0.44
CADD	Uncertain	25
DANN	Uncertain	1.0
DEOGEN2	Benign	0.061	T;T;.;T
Eigen	Pathogenic	0.71
Eigen_PC	Pathogenic	0.67
FATHMM_MKL	Uncertain	0.85	D
M_CAP	Pathogenic	0.59	D
MetaRNN	Pathogenic	0.97	D;D;D;D
MetaSVM	Pathogenic	0.97	D
MutationAssessor	Pathogenic	3.4	M;M;.;.
MutationTaster	Benign	1.0	D
PrimateAI	Uncertain	0.66	T
PROVEAN	Pathogenic	-5.0	D;.;.;D
REVEL	Pathogenic	0.90
Sift	Pathogenic	0.0	D;.;.;D
Sift4G	Uncertain	0.033	D;.;.;.
Polyphen		1.0	D;D;.;.
Vest4		0.89
MutPred		0.85		Gain of disorder (P = 0.0898);Gain of disorder (P = 0.0898);Gain of disorder (P = 0.0898);Gain of disorder (P = 0.0898);
MVP		0.97
MPC		0.27
ClinPred		0.99	D
GERP RS		5.1
Varity_R		0.96
gMVP		0.78

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: rs33918778; hg19: chr11-5247999; COSMIC: COSV100092899; COSMIC: COSV100092899;