chr21-43774230-G-C

Position:

• chr21-43774230-G-C

Variant summary

Our verdict is Uncertain significance. Variant got 2 ACMG points: 4P and 2B. PM1 PM2 BP4_Moderate

The NM_000100.4(CSTB):​c.269C>G​(p.Ala90Gly) variant causes a missense change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.000018 in 1,614,126 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a benign outcome for this variant. 15/20 in silico tools predict a benign outcome for this variant. Variant has been reported in ClinVar as Uncertain significance (★).

• Frequency:
  • Genomes: 𝑓 0.000020 (0 hom., cov: 33)
  • Exomes 𝑓: 0.000018 (0 hom.)
• Consequence: CSTB NM_000100.4 missense
• Clinical Significance: Uncertain significance criteria provided, single submitter U:1
• Conservation: PhyloP100: 0.650

Genes affected

CSTB (HGNC:2482): (cystatin B) The cystatin superfamily encompasses proteins that contain multiple cystatin-like sequences. Some of the members are active cysteine protease inhibitors, while others have lost or perhaps never acquired this inhibitory activity. There are three inhibitory families in the superfamily, including the type 1 cystatins (stefins), type 2 cystatins and kininogens. This gene encodes a stefin that functions as an intracellular thiol protease inhibitor. The protein is able to form a dimer stabilized by noncovalent forces, inhibiting papain and cathepsins l, h and b. The protein is thought to play a role in protecting against the proteases leaking from lysosomes. Evidence indicates that mutations in this gene are responsible for the primary defects in patients with progressive myoclonic epilepsy (EPM1). One type of mutation responsible for EPM1 is the expansion in the promoter region of this gene of a CCCCGCCCCGCG repeat from 2-3 copies to 30-78 copies. [provided by RefSeq, Jul 2016]

CSTB (HGNC:):

ACMG classification

Verdict is Uncertain_significance. Variant got 2 ACMG points.

• PM1: In a chain Cystatin-B (size 97) in uniprot entity CYTB_HUMAN there are 6 pathogenic changes around while only 2 benign (75%) in NM_000100.4
• PM2: Very rare variant in population databases, with high coverage
• BP4: Computational evidence support a benign effect (MetaRNN=0.077572554).

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
CSTB	NM_000100.4	c.269C>G	p.Ala90Gly	missense_variant	3/3	ENST00000291568.7	NP_000091.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
CSTB	ENST00000291568.7	c.269C>G	p.Ala90Gly	missense_variant	3/3	1	NM_000100.4	ENSP00000291568.6

Frequencies

GnomAD3 genomes AF: 0.0000197 AC: 3 AN: 152236 Hom.: 0 Cov.: 33

Gnomad AFR AF: 0.0000241

Gnomad AMI AF: 0.00

Gnomad AMR AF: 0.00

Gnomad ASJ AF: 0.00

Gnomad EAS AF: 0.00

Gnomad SAS AF: 0.00

Gnomad FIN AF: 0.00

Gnomad MID AF: 0.00

Gnomad NFE AF: 0.0000294

Gnomad OTH AF: 0.00

GnomAD4 exome AF: 0.0000178 AC: 26 AN: 1461890 Hom.: 0 Cov.: 31 AF XY: 0.0000138 AC XY: 10 AN XY: 727248

Gnomad4 AFR exome AF: 0.0000299

Gnomad4 AMR exome AF: 0.00

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.00

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.0000225

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome AF: 0.0000197 AC: 3 AN: 152236 Hom.: 0 Cov.: 33 AF XY: 0.0000269 AC XY: 2 AN XY: 74370

Gnomad4 AFR AF: 0.0000241

Gnomad4 AMR AF: 0.00

Gnomad4 ASJ AF: 0.00

Gnomad4 EAS AF: 0.00

Gnomad4 SAS AF: 0.00

Gnomad4 FIN AF: 0.00

Gnomad4 NFE AF: 0.0000294

Gnomad4 OTH AF: 0.00

Alfa AF: 0.0000847 Hom.: 0

Bravo AF: 0.0000227

ESP6500AA AF: 0.00 AC: 0

ESP6500EA AF: 0.000116 AC: 1

EpiCase AF: 0.0000545

EpiControl AF: 0.00

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:1

Revision: criteria provided, single submitter

Submissions by phenotype

Progressive myoclonic epilepsy Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Jan 15, 2024

This sequence change replaces alanine, which is neutral and non-polar, with glycine, which is neutral and non-polar, at codon 90 of the CSTB protein (p.Ala90Gly). This variant is present in population databases (rs138337167, gnomAD 0.007%). This variant has not been reported in the literature in individuals affected with CSTB-related conditions. ClinVar contains an entry for this variant (Variation ID: 840825). Algorithms developed to predict the effect of missense changes on protein structure and function output the following: SIFT: "Not Available"; PolyPhen-2: "Benign"; Align-GVGD: "Not Available". The glycine amino acid residue is found in multiple mammalian species, which suggests that this missense change does not adversely affect protein function. Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may create or strengthen a splice site. 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	0.077
BayesDel_addAF	Benign	-0.20	T
BayesDel_noAF	Benign	-0.53
CADD	Benign	12
DANN	Benign	0.95
DEOGEN2	Benign	0.18	T
Eigen	Benign	-0.80
Eigen_PC	Benign	-0.83
FATHMM_MKL	Benign	0.10	N
LIST_S2	Benign	0.25	T
M_CAP	Benign	0.026	D
MetaRNN	Benign	0.078	T
MetaSVM	Benign	-0.85	T
PrimateAI	Benign	0.32	T
PROVEAN	Benign	-1.3	N
REVEL	Benign	0.12
Sift	Benign	0.19	T
Sift4G	Benign	0.16	T
Polyphen		0.0020	B
Vest4		0.036
MVP		0.37
MPC		0.14
ClinPred		0.042	T
GERP RS		1.5
Varity_R		0.33
gMVP		0.17

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

LitVar

Other links and lift over

dbSNP: rs138337167; hg19: chr21-45194111;