15-90803524-G-C

Position:

• chr15-90803524-G-C

Variant summary

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

The NM_000057.4(BLM):​c.3362G>C​(p.Ser1121Thr) variant causes a missense change. The variant allele was found at a frequency of 0.00000822 in 1,460,044 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. S1121I) has been classified as Uncertain significance.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000082 (0 hom.)
• Consequence: BLM NM_000057.4 missense
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:2
• Conservation: PhyloP100: 5.20

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 3 ACMG points.

• PM1: In a mutagenesis_site Decreased slightly DNA Holliday junction binding. (size 0) in uniprot entity BLM_HUMAN
• PM2: Very rare variant in population databases, with high coverage
• BP4: Computational evidence support a benign effect (MetaRNN=0.27439517).

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
BLM	NM_000057.4	c.3362G>C	p.Ser1121Thr	missense_variant	18/22	ENST00000355112.8

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
BLM	ENST00000355112.8	c.3362G>C	p.Ser1121Thr	missense_variant	18/22	1	NM_000057.4	P2

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 0.00000822 AC: 12 AN: 1460044 Hom.: 0 Cov.: 31 AF XY: 0.00000964 AC XY: 7 AN XY: 726392

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: 0.00000991

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

Aug 10, 2023

This sequence change replaces serine, which is neutral and polar, with threonine, which is neutral and polar, at codon 1121 of the BLM protein (p.Ser1121Thr). This variant is not present in population databases (gnomAD no frequency). This variant has not been reported in the literature in individuals affected with BLM-related conditions. ClinVar contains an entry for this variant (Variation ID: 648358). Advanced modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) performed at Invitae indicates that this missense variant is not expected to disrupt BLM protein function. 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

May 23, 2023

The p.S1121T variant (also known as c.3362G>C), located in coding exon 17 of the BLM gene, results from a G to C substitution at nucleotide position 3362. The serine at codon 1121 is replaced by threonine, an amino acid with similar properties. This amino acid position is not well conserved in available vertebrate species. 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	0.085
BayesDel_addAF	Benign	-0.064	T
BayesDel_noAF	Benign	-0.33
CADD	Benign	18
DANN	Uncertain	0.98
DEOGEN2	Benign	0.25	T
Eigen	Benign	0.17
Eigen_PC	Uncertain	0.31
FATHMM_MKL	Uncertain	0.78	D
LIST_S2	Benign	0.78	T
M_CAP	Benign	0.011	T
MetaRNN	Benign	0.27	T
MetaSVM	Benign	-0.94	T
MutationAssessor	Benign	1.7	L
MutationTaster	Benign	1.0	D;D
PrimateAI	Uncertain	0.54	T
PROVEAN	Benign	-2.3	N
REVEL	Benign	0.19
Sift	Benign	0.075	T
Sift4G	Benign	0.27	T
Polyphen		0.032	B
Vest4		0.12
MutPred		0.57		Loss of ubiquitination at K1122 (P = 0.0607);
MVP		0.82
MPC		0.11
ClinPred		0.45	T
GERP RS		5.7
RBP_binding_hub_radar		0.0
RBP_regulation_power_radar		1.1
Varity_R		0.59
gMVP		0.72

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: rs758753168; hg19: chr15-91346754;