3-33072643-C-G

Variant names:

• chr3-33072643-C-G
• rs780523881
• NM_000404.4:c.146G>C

Variant summary

Our verdict is Pathogenic. The variant received 19 ACMG points: 19P and 0B. PM1 PM2 PM5 PP2 PP3_Strong PP5_Very_Strong

The NM_000404.4(GLB1):​c.146G>C​(p.Arg49Pro) variant causes a missense change. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Likely pathogenic (★★). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. R49C) has been classified as Likely pathogenic.

• Frequency: Genomes: not found (cov: 32)
• Consequence: GLB1 NM_000404.4 missense
• Clinical Significance: Likely pathogenic criteria provided, multiple submitters, no conflicts P:2
• Conservation: PhyloP100: 6.17
• Publications: 0 publications found

Genes affected

GLB1 (HGNC:4298): (galactosidase beta 1) This gene encodes a member of the glycosyl hydrolase 35 family of proteins. Alternative splicing results in multiple transcript variants, at least one of which encodes a preproprotein that is proteolytically processed to generate the mature lysosomal enzyme. This enzyme catalyzes the hydrolysis of a terminal beta-linked galactose residue from ganglioside substrates and other glycoconjugates. Mutations in this gene may result in GM1-gangliosidosis and Morquio B syndrome. [provided by RefSeq, Nov 2015]

GLB1 Gene-Disease associations (from GenCC):

• GM1 gangliosidosis

  Inheritance: AR Classification: DEFINITIVE Submitted by: Myriad Women’s Health, ClinGen
• GM1 gangliosidosis type 3

  Inheritance: AR Classification: DEFINITIVE, STRONG, SUPPORTIVE Submitted by: Orphanet, Labcorp Genetics (formerly Invitae), G2P, Genomics England PanelApp
• mucopolysaccharidosis type 4B

  Inheritance: AR Classification: DEFINITIVE, STRONG, SUPPORTIVE Submitted by: Orphanet, ClinGen, Labcorp Genetics (formerly Invitae), Genomics England PanelApp
• GM1 gangliosidosis type 1

  Inheritance: AR Classification: STRONG, SUPPORTIVE Submitted by: Genomics England PanelApp, Orphanet
• GM1 gangliosidosis type 2

  Inheritance: AR Classification: STRONG, SUPPORTIVE Submitted by: Orphanet, Genomics England PanelApp

ACMG classification

Our verdict: Pathogenic. The variant received 19 ACMG points.

• PM1: In a hotspot region, there are 8 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 0 benign, 2 uncertain in NM_000404.4
• PM2: Very rare variant in population databases, with high coverage
• PM5: Other missense variant is known to change same aminoacid residue: Variant chr3-33072644-G-A is described in ClinVar as Conflicting_classifications_of_pathogenicity. ClinVar VariationId is 923.
• PP2: Missense variant in the gene, where a lot of missense mutations are associated with disease in ClinVar. The gene has 110 curated pathogenic missense variants (we use a threshold of 10). The gene has 24 curated benign missense variants. Gene score misZ: 0.79419 (below the threshold of 3.09). Trascript score misZ: 1.1264 (below the threshold of 3.09). GenCC associations: The gene is linked to mucopolysaccharidosis type 4B, GM1 gangliosidosis, GM1 gangliosidosis type 2, GM1 gangliosidosis type 3, GM1 gangliosidosis type 1.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.973
• PP5: Variant 3-33072643-C-G is Pathogenic according to our data. Variant chr3-33072643-C-G is described in ClinVar as Likely_pathogenic. ClinVar VariationId is 3251806.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
GLB1	NM_000404.4	c.146G>C	p.Arg49Pro	missense_variant	Exon 2 of 16	ENST00000307363.10	NP_000395.3

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
GLB1	ENST00000307363.10	c.146G>C	p.Arg49Pro	missense_variant	Exon 2 of 16	1	NM_000404.4	ENSP00000306920.4

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome Cov.: 31

GnomAD4 genome Cov.: 32

ClinVar

Significance: Likely pathogenic

Submissions summary: Pathogenic:2

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

GM1 gangliosidosis Pathogenic:1

Apr 22, 2024

Women's Health and Genetics/Laboratory Corporation of America, LabCorp

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Variant summary: GLB1 c.146G>C (p.Arg49Pro) results in a non-conservative amino acid change located in the Glycoside hydrolase 35, catalytic domain (IPR031330) of the encoded protein sequence. Five of five in-silico tools predict a damaging effect of the variant on protein function. The variant was absent in 249538 control chromosomes. To our knowledge, no occurrence of c.146G>C in individuals affected with GM1 Gangliosidosis and no experimental evidence demonstrating its impact on protein function have been reported. However, different variants affecting the same codon have been classified as pathogenic by our lab (c.145C>T, p.Arg49Cys) or as pathogenic in ClinVar (c.146G>A, p.Arg49His) supporting the critical relevance of codon 49 to GLB1 protein function. No submitters have cited clinical-significance assessments for this variant to ClinVar. Based on the evidence outlined above, the variant was classified as likely pathogenic. -

Mucopolysaccharidosis, MPS-IV-B;C0268271:Infantile GM1 gangliosidosis;C0268272:GM1 gangliosidosis type 2;C0268273:GM1 gangliosidosis type 3 Pathogenic:1

May 13, 2024

Fulgent Genetics, Fulgent Genetics

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

- -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.82
BayesDel_addAF	Pathogenic	0.53	D
BayesDel_noAF	Pathogenic	0.52
CADD	Pathogenic	29
DANN	Uncertain	1.0
DEOGEN2	Uncertain	0.68	.;.;.;.;D
Eigen	Pathogenic	0.71
Eigen_PC	Pathogenic	0.68
FATHMM_MKL	Pathogenic	0.98	D
LIST_S2	Pathogenic	0.98	.;.;D;D;D
M_CAP	Pathogenic	0.50	D
MetaRNN	Pathogenic	0.97	D;D;D;D;D
MetaSVM	Pathogenic	1.1	D
PhyloP100		6.2
PrimateAI	Uncertain	0.53	T
PROVEAN	Pathogenic	-5.9	D;D;D;D;D
REVEL	Pathogenic	0.95
Sift	Uncertain	0.0010	D;D;D;D;D
Sift4G	Uncertain	0.0020	D;D;D;.;D
Polyphen		1.0	.;.;D;.;.
Vest4		0.96
MutPred		0.84		Loss of methylation at R49 (P = 0.022);.;Loss of methylation at R49 (P = 0.022);.;.;
MVP		0.99
MPC		1.1
ClinPred		1.0	D
GERP RS		5.0
gMVP		0.97
Mutation Taster		=7/93	disease causing

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

Other links and lift over

dbSNP: rs780523881; hg19: chr3-33114135;