15-90749509-A-G

Position:

• chr15-90749509-A-G

Variant summary

Our verdict is Likely benign. Variant got -2 ACMG points: 2P and 4B. PM2 BP4_Strong

The NM_000057.4(BLM):​c.241A>G​(p.Thr81Ala) variant causes a missense change involving the alteration of a non-conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a benign outcome for this variant. 15/21 in silico tools predict a benign outcome for this variant. Variant has been reported in ClinVar as Uncertain significance (★★).

• Frequency: Genomes: not found (cov: 32)
• Consequence: BLM NM_000057.4 missense
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:3
• Conservation: PhyloP100: -0.0980

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 Likely_benign. Variant got -2 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• BP4: Computational evidence support a benign effect (MetaRNN=0.05851099).

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
BLM	NM_000057.4	c.241A>G	p.Thr81Ala	missense_variant	3/22	ENST00000355112.8	NP_000048.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
BLM	ENST00000355112.8	c.241A>G	p.Thr81Ala	missense_variant	3/22	1	NM_000057.4	ENSP00000347232	P2

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome Cov.: 31

GnomAD4 genome Cov.: 32

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:3

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Bloom syndrome Uncertain:2

Uncertain significance, criteria provided, single submitter	clinical testing	Mendelics	Jul 02, 2018	- -
Uncertain significance, criteria provided, single submitter	clinical testing	Labcorp Genetics (formerly Invitae), Labcorp	Oct 05, 2022	This sequence change replaces threonine, which is neutral and polar, with alanine, which is neutral and non-polar, at codon 81 of the BLM protein (p.Thr81Ala). 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: 405289). Algorithms developed to predict the effect of missense changes on protein structure and function output the following: SIFT: "Tolerated"; PolyPhen-2: "Benign"; Align-GVGD: "Class C0". The alanine amino acid residue is found in multiple mammalian species, which suggests that this missense change does not adversely affect 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

Jan 18, 2018

The p.T81A variant (also known as c.241A>G), located in coding exon 2 of the BLM gene, results from an A to G substitution at nucleotide position 241. The threonine at codon 81 is replaced by alanine, an amino acid with similar properties. This amino acid position is poorly 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	0.060
BayesDel_addAF	Benign	-0.37	T
BayesDel_noAF	Benign	-0.76
CADD	Benign	0.37
DANN	Benign	0.44
DEOGEN2	Benign	0.048	T;.
Eigen	Benign	-1.2
Eigen_PC	Benign	-1.2
FATHMM_MKL	Benign	0.027	N
LIST_S2	Benign	0.46	T;T
M_CAP	Benign	0.0064	T
MetaRNN	Benign	0.059	T;T
MetaSVM	Benign	-1.1	T
MutationAssessor	Benign	1.4	L;.
MutationTaster	Benign	1.0	N;N
PrimateAI	Benign	0.25	T
PROVEAN	Benign	-0.40	N;N
REVEL	Benign	0.031
Sift	Benign	1.0	T;T
Sift4G	Benign	0.81	T;T
Polyphen		0.0	B;.
Vest4		0.044
MutPred		0.092		Gain of helix (P = 0.062);Gain of helix (P = 0.062);
MVP		0.60
MPC		0.087
ClinPred		0.034	T
GERP RS		-3.1
RBP_binding_hub_radar		0.0
RBP_regulation_power_radar		1.1
Varity_R		0.017
gMVP		0.057

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.020		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: rs1060500637; hg19: chr15-91292739;