22-19723949-C-T

Variant summary

Our verdict is Uncertain significance. Variant got 3 ACMG points: 4P and 1B. PM1 PM2 BP4

The NM_000407.5(GP1BB):c.106C>T(p.Leu36Phe) variant causes a missense change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.00000584 in 1,370,958 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a benign outcome for this variant. 14/20 in silico tools predict a benign outcome for this variant. Variant has been reported in ClinVar as Uncertain significance (★).

• Frequency:
  • Genomes: not found (cov: 33)
  • Exomes 𝑓: 0.0000058 (0 hom.)
• Consequence: GP1BB NM_000407.5 missense
• Clinical Significance: Uncertain significance criteria provided, single submitter U:1
• Conservation: PhyloP100: 0.742

Genes affected

GP1BB (HGNC:4440): (glycoprotein Ib platelet subunit beta) Platelet glycoprotein Ib (GPIb) is a heterodimeric transmembrane protein consisting of a disulfide-linked 140 kD alpha chain and 22 kD beta chain. It is part of the GPIb-V-IX system that constitutes the receptor for von Willebrand factor (VWF), and mediates platelet adhesion in the arterial circulation. GPIb alpha chain provides the VWF binding site, and GPIb beta contributes to surface expression of the receptor and participates in transmembrane signaling through phosphorylation of its intracellular domain. Mutations in the GPIb beta subunit have been associated with Bernard-Soulier syndrome, velocardiofacial syndrome and giant platelet disorder. The 206 amino acid precursor of GPIb beta is synthesized from a 1.0 kb mRNA expressed in plateletes and megakaryocytes. A 411 amino acid protein arising from a longer, unspliced transcript in endothelial cells has been described; however, the authenticity of this product has been questioned. Yet another less abundant GPIb beta mRNA species of 3.5 kb, expressed in nonhematopoietic tissues such as endothelium, brain and heart, was shown to result from inefficient usage of a non-consensus polyA signal in the neighboring upstream gene (SEPT5, septin 5). In the absence of polyadenylation from its own imperfect site, the SEPT5 gene produces read-through transcripts that use the consensus polyA signal of this gene. [provided by RefSeq, Dec 2010]

SEPT5-GP1BB (HGNC:):

SEPTIN5 (HGNC:9164): (septin 5) This gene is a member of the septin gene family of nucleotide binding proteins, originally described in yeast as cell division cycle regulatory proteins. Septins are highly conserved in yeast, Drosophila, and mouse and appear to regulate cytoskeletal organization. Disruption of septin function disturbs cytokinesis and results in large multinucleate or polyploid cells. This gene is mapped to 22q11, the region frequently deleted in DiGeorge and velocardiofacial syndromes. A translocation involving the MLL gene and this gene has also been reported in patients with acute myeloid leukemia. Alternative splicing results in multiple transcript variants. The presence of a non-consensus polyA signal (AACAAT) in this gene also results in read-through transcription into the downstream neighboring gene (GP1BB; platelet glycoprotein Ib), whereby larger, non-coding transcripts are produced. [provided by RefSeq, Dec 2010]

ACMG classification

Verdict is Uncertain_significance. Variant got 3 ACMG points.

• PM1: In a chain Platelet glycoprotein Ib beta chain (size 180) in uniprot entity GP1BB_HUMAN there are 37 pathogenic changes around while only 2 benign (95%) in NM_000407.5
• PM2: Very rare variant in population databases, with high coverage
• BP4: Computational evidence support a benign effect (MetaRNN=0.29943103).

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
GP1BB	NM_000407.5	c.106C>T	p.Leu36Phe	missense_variant	2/2	ENST00000366425.4
SEPT5-GP1BB	NR_037611.1	n.3846C>T		non_coding_transcript_exon_variant	12/12
SEPT5-GP1BB	NR_037612.1	n.2350C>T		non_coding_transcript_exon_variant	12/12

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
GP1BB	ENST00000366425.4	c.106C>T	p.Leu36Phe	missense_variant	2/2	1	NM_000407.5	P1
SEPTIN5	ENST00000470814.1	n.2078C>T		non_coding_transcript_exon_variant	6/6	5

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome AF: 0.00000584 AC: 8 AN: 1370958 Hom.: 0 Cov.: 32 AF XY: 0.00000443 AC XY: 3 AN XY: 677028

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: 0.0000128

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.00000652

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 33

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:1

Revision: criteria provided, single submitter

Submissions by phenotype

Abnormal bleeding Uncertain:1

Uncertain significance, criteria provided, single submitter

research

NIHR Bioresource Rare Diseases, University of Cambridge

Feb 01, 2019

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Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Benign	0.20
BayesDel_addAF	Benign	-0.078	T
BayesDel_noAF	Benign	-0.35
Cadd	Benign	19
Dann	Benign	0.95
DEOGEN2	Benign	0.35	T
Eigen	Benign	-0.74
Eigen_PC	Benign	-0.76
FATHMM_MKL	Benign	0.69	D
LIST_S2	Uncertain	0.86	D
M_CAP	Pathogenic	0.83	D
MetaRNN	Benign	0.30	T
MetaSVM	Uncertain	-0.19	T
MutationAssessor	Benign	-0.34	N
MutationTaster	Benign	1.0	N
PROVEAN	Benign	-1.3	N
REVEL	Benign	0.26
Sift	Benign	0.12	T
Sift4G	Benign	0.19	T
Polyphen		0.78	P
Vest4		0.081
MutPred		0.37		Loss of sheet (P = 0.0457);
MVP		0.97
MPC		0.83
ClinPred		0.25	T
GERP RS		2.8
Varity_R		0.16
gMVP		0.21

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: rs1601248319; hg19: chr22-19711472;