chr15-90763023-T-C

Variant names:

• chr15-90763023-T-C
• rs1555420162
• NM_000057.4:c.1940T>C

Variant summary

Our verdict is Uncertain significance. The variant received 1 ACMG points: 2P and 1B. PM2 BP4

The NM_000057.4(BLM):​c.1940T>C​(p.Leu647Pro) variant causes a missense change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.000000684 in 1,461,584 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts 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. L647V) has been classified as Uncertain significance.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 6.8e-7 (0 hom.)
• Consequence: BLM NM_000057.4 missense
• Clinical Significance: Uncertain significance criteria provided, single submitter U:1
• Conservation: PhyloP100: 3.33
• Publications: 0 publications found

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]

BLM Gene-Disease associations (from GenCC):

• Bloom syndrome

  Inheritance: AR Classification: DEFINITIVE, STRONG, MODERATE, SUPPORTIVE Submitted by: Myriad Women’s Health, Labcorp Genetics (formerly Invitae), G2P, Laboratory for Molecular Medicine, Orphanet, Genomics England PanelApp, ClinGen
• osteosarcoma

  Inheritance: AR Classification: MODERATE Submitted by: Genomics England PanelApp
• breast cancer

  Inheritance: AD Classification: NO_KNOWN Submitted by: Ambry Genetics
• hereditary nonpolyposis colon cancer

  Inheritance: AD Classification: NO_KNOWN Submitted by: Ambry Genetics

ACMG classification

Our verdict: Uncertain_significance. The variant received 1 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• BP4: Computational evidence support a benign effect (MetaRNN=0.29816276).

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
BLM	NM_000057.4	c.1940T>C	p.Leu647Pro	missense_variant	Exon 8 of 22	ENST00000355112.8	NP_000048.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
BLM	ENST00000355112.8	c.1940T>C	p.Leu647Pro	missense_variant	Exon 8 of 22	1	NM_000057.4	ENSP00000347232.3

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 6.84e-7 AC: 1 AN: 1461584 Hom.: 0 Cov.: 31 AF XY: 0.00000138 AC XY: 1 AN XY: 727078

African (AFR) AF: 0.00 AC: 0 AN: 33446

American (AMR) AF: 0.00 AC: 0 AN: 44656

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 26130

East Asian (EAS) AF: 0.00 AC: 0 AN: 39692

South Asian (SAS) AF: 0.00 AC: 0 AN: 86170

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53406

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 5766

European-Non Finnish (NFE) AF: 8.99e-7 AC: 1 AN: 1111932

Other (OTH) AF: 0.00 AC: 0 AN: 60386

GnomAD4 genome Cov.: 32

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:1

Revision: criteria provided, single submitter

Submissions by phenotype

Bloom syndrome Uncertain:1

Jun 01, 2019

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This sequence change replaces leucine with proline at codon 647 of the BLM protein (p.Leu647Pro). The leucine residue is weakly conserved and there is a moderate physicochemical difference between leucine and proline. 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 disease. Algorithms developed to predict the effect of missense changes on protein structure and function 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. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Benign	0.13
BayesDel_addAF	Uncertain	0.070	D
BayesDel_noAF	Benign	-0.14
CADD	Benign	23
DANN	Uncertain	1.0
DEOGEN2	Benign	0.26	T;.
Eigen	Benign	0.048
Eigen_PC	Benign	0.18
FATHMM_MKL	Uncertain	0.96	D
LIST_S2	Benign	0.76	T;T
M_CAP	Uncertain	0.087	D
MetaRNN	Benign	0.30	T;T
MetaSVM	Benign	-0.36	T
MutationAssessor	Uncertain	2.1	M;.
PhyloP100		3.3
PrimateAI	Uncertain	0.51	T
PROVEAN	Pathogenic	-4.5	D;D
REVEL	Uncertain	0.40
Sift	Uncertain	0.0090	D;D
Sift4G	Uncertain	0.017	D;D
Polyphen		0.077	B;.
Vest4		0.46
MutPred		0.47		Gain of disorder (P = 0.0339);Gain of disorder (P = 0.0339);
MVP		0.84
MPC		0.53
ClinPred		0.97	D
GERP RS		5.5
Varity_R		0.78
gMVP		0.85

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

Other links and lift over

dbSNP: rs1555420162; hg19: chr15-91306253;