chr15-90763010-C-A

Position:

• chr15-90763010-C-A

Variant summary

Our verdict is Uncertain significance. Variant got 0 ACMG points: 2P and 2B. PM2 BP4_Moderate

The NM_000057.4(BLM):​c.1927C>A​(p.Arg643Ser) variant causes a missense change. The variant allele was found at a frequency of 0.00000205 in 1,461,182 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a benign outcome for this variant. 12/21 in silico tools predict a benign outcome for this variant. Variant has been reported in ClinVar as Uncertain significance (★★). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. R643H) has been classified as Likely benign.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000021 (0 hom.)
• Consequence: BLM NM_000057.4 missense
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:2
• Conservation: PhyloP100: 4.67

Genes affected

BLM (HGNC:1058): (BLM RecQ like helicase) The Bloom syndrome is an autosomal recessive disorder characterized by growth deficiency, microcephaly and immunodeficiency among others. It is caused by homozygous or compound heterozygous mutation in the gene encoding DNA helicase RecQ protein on chromosome 15q26. This Bloom-associated helicase unwinds a variety of DNA substrates including Holliday junction, and is involved in several pathways contributing to the maintenance of genome stability. Identification of pathogenic Bloom variants is required for heterozygote testing in at-risk families. [provided by RefSeq, May 2020]

ACMG classification

Verdict is Uncertain_significance. Variant got 0 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• BP4: Computational evidence support a benign effect (MetaRNN=0.16194987).

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
BLM	NM_000057.4	c.1927C>A	p.Arg643Ser	missense_variant	8/22	ENST00000355112.8

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
BLM	ENST00000355112.8	c.1927C>A	p.Arg643Ser	missense_variant	8/22	1	NM_000057.4	P2

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 0.00000205 AC: 3 AN: 1461182 Hom.: 0 Cov.: 31 AF XY: 0.00000138 AC XY: 1 AN XY: 726834

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: 0.00000180

Gnomad4 OTH exome AF: 0.0000166

GnomAD4 genome Cov.: 32

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:2

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Bloom syndrome Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Jun 17, 2020

This sequence change replaces arginine with serine at codon 643 of the BLM protein (p.Arg643Ser). The arginine residue is weakly conserved and there is a moderate physicochemical difference between arginine and serine. This variant is not present in population databases (ExAC no frequency). This variant has not been reported in the literature in individuals with BLM-related conditions. Algorithms developed to predict the effect of missense changes on protein structure and function are either unavailable or do not agree on the potential impact of this missense change (SIFT: "Tolerated"; PolyPhen-2: "Possibly Damaging"; Align-GVGD: "Class C0"). In summary, the available evidence is currently insufficient to determine the role of this variant in disease. Therefore, it has been classified as a Variant of Uncertain Significance. -

Hereditary cancer-predisposing syndrome Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Ambry Genetics

Jul 26, 2022

The p.R643S variant (also known as c.1927C>A), located in coding exon 7 of the BLM gene, results from a C to A substitution at nucleotide position 1927. The arginine at codon 643 is replaced by serine, an amino acid with dissimilar properties. This amino acid position is conserved. In addition, this alteration is predicted to be tolerated by in silico analysis. Since supporting evidence is limited at this time, the clinical significance of this alteration remains unclear. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Benign	0.14
BayesDel_addAF	Benign	-0.011	T
BayesDel_noAF	Benign	-0.25
CADD	Benign	17
DANN	Uncertain	0.99
DEOGEN2	Benign	0.13	T;.
Eigen	Benign	-0.24
Eigen_PC	Benign	-0.17
FATHMM_MKL	Pathogenic	0.98	D
LIST_S2	Benign	0.80	T;T
M_CAP	Uncertain	0.087	D
MetaRNN	Benign	0.16	T;T
MetaSVM	Benign	-0.41	T
MutationAssessor	Benign	1.8	L;.
MutationTaster	Benign	0.75	D;D
PrimateAI	Benign	0.20	T
PROVEAN	Uncertain	-2.6	D;D
REVEL	Benign	0.19
Sift	Uncertain	0.012	D;D
Sift4G	Benign	0.063	T;T
Polyphen		0.019	B;.
Vest4		0.28
MutPred		0.33		Gain of ubiquitination at K640 (P = 0.0338);Gain of ubiquitination at K640 (P = 0.0338);
MVP		0.83
MPC		0.26
ClinPred		0.87	D
GERP RS		4.5
Varity_R		0.64
gMVP		0.66

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

No publications associated with this variant yet.

Other links and lift over

hg19: chr15-91306240;