Genetic Variant HEXB:p.Pro58AlafsTer57 (chr5-74685429-T-TG) – ACMG Classification: Pathogenic (10 pts)

Variant summary

Our verdict is Pathogenic. The variant received 10 ACMG points: 10P and 0B. PVS1PM2

The NM_000521.4(HEXB):c.171dupG(p.Pro58AlafsTer57) variant causes a frameshift change. The variant allele was found at a frequency of 0.000000688 in 1,453,052 control chromosomes in the GnomAD database, with no homozygous occurrence. No clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar. Synonymous variant affecting the same amino acid position (i.e. P58P) has been classified as Likely benign. Variant results in nonsense mediated mRNA decay.

Frequency

Genomes: not found (cov: 31)

Exomes 𝑓: 6.9e-7 ( 0 hom. )

Consequence

HEXB
NM_000521.4 frameshift

Scores

Not classified

Clinical Significance

Not reported in ClinVar

Conservation

PhyloP100: 5.59

Publications

3 publications found

Variant links:

Genes affected

HEXB (HGNC:4879): (hexosaminidase subunit beta) Hexosaminidase B is the beta subunit of the lysosomal enzyme beta-hexosaminidase that, together with the cofactor GM2 activator protein, catalyzes the degradation of the ganglioside GM2, and other molecules containing terminal N-acetyl hexosamines. Beta-hexosaminidase is composed of two subunits, alpha and beta, which are encoded by separate genes. Both beta-hexosaminidase alpha and beta subunits are members of family 20 of glycosyl hydrolases. Mutations in the alpha or beta subunit genes lead to an accumulation of GM2 ganglioside in neurons and neurodegenerative disorders termed the GM2 gangliosidoses. Beta subunit gene mutations lead to Sandhoff disease (GM2-gangliosidosis type II). Alternatively spliced transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, May 2014]

HEXB Gene-Disease associations (from GenCC):

Sandhoff disease
Inheritance: AR Classification: DEFINITIVE, STRONG Submitted by: Labcorp Genetics (formerly Invitae), Ambry Genetics, G2P, ClinGen, Genomics England PanelApp, Myriad Women’s Health

HEXB links:

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ACMG classification

Classification was made for transcript

Our verdict: Pathogenic. The variant received 10 ACMG points.

PVS1

Loss of function variant, product undergoes nonsense mediated mRNA decay. LoF is a known mechanism of disease.

PM2

Very rare variant in population databases, with high coverage;

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
HEXB	NM_000521.4 link	c.171dupG	p.Pro58AlafsTer57	frameshift_variant	Exon 1 of 14	ENST00000261416.12	NP_000512.2	P07686A0A024RAJ6
HEXB	NM_001292004.2 link	c.-376-3897dupG		intron_variant	Intron 1 of 13		NP_001278933.1	P07686Q5URX0

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	UniProt
HEXB	ENST00000261416.12 link	c.171dupG	p.Pro58AlafsTer57	frameshift_variant	Exon 1 of 14	1	NM_000521.4	ENSP00000261416.7	P07686
HEXB	ENST00000511181.5 link	c.-376-3897dupG		intron_variant	Intron 1 of 13	1		ENSP00000426285.1	Q5URX0
HEXB	ENST00000513079.5 link	n.236dupG		non_coding_transcript_exon_variant	Exon 1 of 6	2
HEXB	ENST00000515528.1 link	n.226dupG		non_coding_transcript_exon_variant	Exon 1 of 2	2

Frequencies

GnomAD3 genomes

Cov.:

GnomAD2 exomes

AF:

0.00000445

AC:

AN:

224844

AF XY:

0.00000803

show subpopulations

Gnomad AFR exome

AF:

0.00

Gnomad AMR exome

AF:

0.00

Gnomad ASJ exome

AF:

0.00

Gnomad EAS exome

AF:

0.00

Gnomad FIN exome

AF:

0.0000499

Gnomad NFE exome

AF:

0.00

Gnomad OTH exome

AF:

0.00

GnomAD4 exome

AF:

6.88e-7

AC:

AN:

1453052

Hom.:

Cov.:

AF XY:

0.00000138

AC XY:

AN XY:

722488

show subpopulations

⚠️ The allele balance in gnomAD version 4 Exomes is significantly skewed from the expected value of 0.5.

African (AFR)

AF:

0.00

AC:

AN:

33128

American (AMR)

AF:

0.00

AC:

AN:

43934

Ashkenazi Jewish (ASJ)

AF:

0.00

AC:

AN:

25934

East Asian (EAS)

AF:

0.00

AC:

AN:

39020

South Asian (SAS)

AF:

0.00

AC:

AN:

85390

European-Finnish (FIN)

AF:

0.0000197

AC:

AN:

50882

Middle Eastern (MID)

AF:

0.00

AC:

AN:

5756

European-Non Finnish (NFE)

AF:

0.00

AC:

AN:

1109062

Other (OTH)

AF:

0.00

AC:

AN:

59946

⚠️ The allele balance in gnomAD4 Exomes is highly skewed from 0.5 (p-value = 0.000000), which strongly suggests a high chance of mosaicism in these individuals.

Allele Balance Distribution

Red line indicates average allele balance

Average allele balance: 0.325

Heterozygous variant carriers

0.00

0.20

0.40

0.60

0.80

0.95

Allele balance

GnomAD4 genome

Cov.:

ClinVar

Not reported in ClinVar

Computational scores

Source: dbNSFP v4.3

Name

Calibrated prediction

Score

Prediction

PhyloP100

5.6

Mutation Taster

=3/197

disease causing (fs/PTC)

(source)

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

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5-74685429-TG-TGG

Variant summary

Frequency

Consequence

Scores

Clinical Significance

Conservation

Publications

ACMG classification

Transcripts

RefSeq

Ensembl

Frequencies

ClinVar

Computational scores

Splicing

Publications

Other links and lift over