20-33851022-A-G

Variant names:

• chr20-33851022-A-G
• rs775409766
• NM_176812.5:c.439A>G

Variant summary

Our verdict is Uncertain significance. The variant received 2 ACMG points: 3P and 1B. PM2 PP2 BP4

The NM_176812.5(CHMP4B):​c.439A>G​(p.Thr147Ala) variant causes a missense change. The variant allele was found at a frequency of 0.00000205 in 1,461,730 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a benign outcome for this variant. 13/22 in silico tools predict a benign outcome for this variant. Variant has been reported in ClinVar as Uncertain significance (★).

• Frequency:
  • Genomes: not found (cov: 33)
  • Exomes 𝑓: 0.0000021 (0 hom.)
• Consequence: CHMP4B NM_176812.5 missense
• Clinical Significance: Uncertain significance criteria provided, single submitter U:1
• Conservation: PhyloP100: 6.14
• Publications: 0 publications found

Genes affected

CHMP4B (HGNC:16171): (charged multivesicular body protein 4B) This gene encodes a member of the chromatin-modifying protein/charged multivesicular body protein (CHMP) protein family. The protein is part of the endosomal sorting complex required for transport (ESCRT) complex III (ESCRT-III), which functions in the sorting of endocytosed cell-surface receptors into multivesicular endosomes. The ESCRT machinery also functions in the final abscisson stage of cytokinesis and in the budding of enveloped viruses such as HIV-1. The three proteins of the CHMP4 subfamily interact with programmed cell death 6 interacting protein (PDCD6IP, also known as ALIX), which also functions in the ESCRT pathway. The CHMP4 proteins assemble into membrane-attached 5-nm filaments that form circular scaffolds and promote or stabilize outward budding. These polymers are proposed to help generate the luminal vesicles of multivesicular bodies. Mutations in this gene result in autosomal dominant posterior polar cataracts.[provided by RefSeq, Oct 2009]

CHMP4B Gene-Disease associations (from GenCC):

• cataract 31 multiple types

  Inheritance: AD Classification: STRONG, MODERATE Submitted by: Ambry Genetics, G2P, Labcorp Genetics (formerly Invitae)
• early-onset posterior polar cataract

  Inheritance: AD Classification: SUPPORTIVE Submitted by: Orphanet
• early-onset posterior subcapsular cataract

  Inheritance: AD Classification: SUPPORTIVE Submitted by: Orphanet

ACMG classification

Our verdict: Uncertain_significance. The variant received 2 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP2: Missense variant in the gene, where a lot of missense mutations are associated with disease in ClinVar. The gene has 3 curated pathogenic missense variants (we use a threshold of 10). The gene has 0 curated benign missense variants. Gene score misZ: 2.3781 (below the threshold of 3.09). Trascript score misZ: 2.8898 (below the threshold of 3.09). GenCC associations: The gene is linked to early-onset posterior subcapsular cataract, cataract 31 multiple types, early-onset posterior polar cataract.
• BP4: Computational evidence support a benign effect (MetaRNN=0.26956144).

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
CHMP4B	NM_176812.5	c.439A>G	p.Thr147Ala	missense_variant	Exon 3 of 5	ENST00000217402.3	NP_789782.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
CHMP4B	ENST00000217402.3	c.439A>G	p.Thr147Ala	missense_variant	Exon 3 of 5	1	NM_176812.5	ENSP00000217402.2

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD2 exomes AF: 0.00000795 AC: 2 AN: 251496 AF XY: 0.00

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: 0.00

Gnomad NFE exome AF: 0.00

Gnomad OTH exome AF: 0.00

GnomAD4 exome AF: 0.00000205 AC: 3 AN: 1461730 Hom.: 0 Cov.: 30 AF XY: 0.00000138 AC XY: 1 AN XY: 727188

African (AFR) AF: 0.00 AC: 0 AN: 33480

American (AMR) AF: 0.00 AC: 0 AN: 44724

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 26136

East Asian (EAS) AF: 0.00 AC: 0 AN: 39700

South Asian (SAS) AF: 0.0000348 AC: 3 AN: 86254

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53418

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 5768

European-Non Finnish (NFE) AF: 0.00 AC: 0 AN: 1111866

Other (OTH) AF: 0.00 AC: 0 AN: 60384

GnomAD4 genome Cov.: 33

ExAC AF: 0.00000824 AC: 1

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:1

Revision: criteria provided, single submitter

Submissions by phenotype

not specified Uncertain:1

Sep 16, 2021

Ambry Genetics

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The c.439A>G (p.T147A) alteration is located in exon 3 (coding exon 3) of the CHMP4B gene. This alteration results from a A to G substitution at nucleotide position 439, causing the threonine (T) at amino acid position 147 to be replaced by an alanine (A). Based on insufficient or conflicting evidence, 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	-0.12	T
BayesDel_noAF	Benign	-0.23
CADD	Uncertain	23
DANN	Uncertain	0.99
DEOGEN2	Benign	0.34	T
Eigen	Benign	-0.037
Eigen_PC	Benign	0.22
FATHMM_MKL	Uncertain	0.93	D
LIST_S2	Uncertain	0.92	D
M_CAP	Benign	0.019	T
MetaRNN	Benign	0.27	T
MetaSVM	Benign	-0.86	T
MutationAssessor	Benign	0.10	N
PhyloP100		6.1
PrimateAI	Uncertain	0.61	T
PROVEAN	Benign	-0.93	N
REVEL	Benign	0.17
Sift	Uncertain	0.021	D
Sift4G	Uncertain	0.045	D
Polyphen		0.017	B
Vest4		0.36
MutPred		0.36		Loss of glycosylation at T147 (P = 0.0273);
MVP		0.83
MPC		1.2
ClinPred		0.72	D
GERP RS		6.1
Varity_R		0.093
gMVP		0.59
Mutation Taster		=87/13	polymorphism

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: rs775409766; hg19: chr20-32438828;