rs778381859

Variant names:

• chr22-30614415-GTC-G
• rs778381859
• NM_000355.4:c.497_498delTC

Variant summary

Our verdict is Pathogenic. Variant got 17 ACMG points: 18P and 1B. PVS1 PM2 PP5_Very_Strong BS1_Supporting

The NM_000355.4(TCN2):​c.497_498delTC​(p.Leu166ProfsTer7) variant causes a frameshift change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.000294 in 1,614,022 control chromosomes in the GnomAD database, with no homozygous occurrence. Variant has been reported in ClinVar as Likely pathogenic (★★). Variant results in nonsense mediated mRNA decay.

• Frequency:
  • Genomes: 𝑓 0.00016 (0 hom., cov: 32)
  • Exomes 𝑓: 0.00031 (0 hom.)
• Consequence: TCN2 NM_000355.4 frameshift
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:6 U:1
• Conservation: PhyloP100: 1.44

Genes affected

TCN2 (HGNC:11653): (transcobalamin 2) This gene encodes a member of the vitamin B12-binding protein family. This family of proteins, alternatively referred to as R binders, is expressed in various tissues and secretions. This plasma protein binds cobalamin and mediates the transport of cobalamin into cells. This protein and other mammalian cobalamin-binding proteins, such as transcobalamin I and gastric intrisic factor, may have evolved by duplication of a common ancestral gene. Alternative splicing results in multiple transcript variants.[provided by RefSeq, May 2010]

ACMG classification

Verdict is Pathogenic. Variant got 17 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
• PP5: Variant 22-30614415-GTC-G is Pathogenic according to our data. Variant chr22-30614415-GTC-G is described in ClinVar as [Likely_pathogenic]. Clinvar id is 376919.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.
• BS1: Variant frequency is greater than expected in population nfe. gnomad4_exome allele frequency = 0.000309 (451/1461884) while in subpopulation NFE AF= 0.000382 (425/1112008). AF 95% confidence interval is 0.000352. There are 0 homozygotes in gnomad4_exome. There are 198 alleles in male gnomad4_exome subpopulation. This position pass quality control queck. Existence of Clinvar submissions makes me limit the strength of this signal to Supporting

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
TCN2	NM_000355.4	c.497_498delTC	p.Leu166ProfsTer7	frameshift_variant	Exon 4 of 9	ENST00000215838.8	NP_000346.2
TCN2	NM_001184726.2	c.416_417delTC	p.Leu139ProfsTer7	frameshift_variant	Exon 4 of 9		NP_001171655.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
TCN2	ENST00000215838.8	c.497_498delTC	p.Leu166ProfsTer7	frameshift_variant	Exon 4 of 9	1	NM_000355.4	ENSP00000215838.3

Frequencies

GnomAD3 genomes AF: 0.000158 AC: 24 AN: 152138 Hom.: 0 Cov.: 32

Gnomad AFR AF: 0.000169

Gnomad AMI AF: 0.00

Gnomad AMR AF: 0.0000655

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: 0.000235

Gnomad OTH AF: 0.00

GnomAD3 exomes AF: 0.000119 AC: 30 AN: 251426 Hom.: 0 AF XY: 0.000110 AC XY: 15 AN XY: 135900

Gnomad AFR exome AF: 0.000369

Gnomad AMR exome AF: 0.0000578

Gnomad ASJ exome AF: 0.00

Gnomad EAS exome AF: 0.00

Gnomad SAS exome AF: 0.00

Gnomad FIN exome AF: 0.0000462

Gnomad NFE exome AF: 0.000176

Gnomad OTH exome AF: 0.000163

GnomAD4 exome AF: 0.000309 AC: 451 AN: 1461884 Hom.: 0 AF XY: 0.000272 AC XY: 198 AN XY: 727246

Gnomad4 AFR exome AF: 0.000119

Gnomad4 AMR exome AF: 0.0000671

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.00

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.0000562

Gnomad4 NFE exome AF: 0.000382

Gnomad4 OTH exome AF: 0.000265

GnomAD4 genome AF: 0.000158 AC: 24 AN: 152138 Hom.: 0 Cov.: 32 AF XY: 0.000202 AC XY: 15 AN XY: 74336

Gnomad4 AFR AF: 0.000169

Gnomad4 AMR AF: 0.0000655

Gnomad4 ASJ AF: 0.00

Gnomad4 EAS AF: 0.00

Gnomad4 SAS AF: 0.00

Gnomad4 FIN AF: 0.00

Gnomad4 NFE AF: 0.000235

Gnomad4 OTH AF: 0.00

Alfa AF: 0.000217 Hom.: 0

Bravo AF: 0.000178

EpiCase AF: 0.000436

EpiControl AF: 0.000296

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:6 Uncertain:1

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

not provided Pathogenic:3

Oct 10, 2016

Center for Pediatric Genomic Medicine, Children's Mercy Hospital and Clinics

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

- -

Apr 23, 2018

Eurofins Ntd Llc (ga)

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

- -

May 17, 2023

GeneDx

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Frameshift variant predicted to result in protein truncation or nonsense mediated decay in a gene for which loss-of-function is a known mechanism of disease; This variant is associated with the following publications: (PMID: 30041674, 20352340, 24305960, 32841161) -

Transcobalamin II deficiency Pathogenic:3

Mar 30, 2021

Center for Genomics, Ann and Robert H. Lurie Children's Hospital of Chicago

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

TCN2 NM_000355.3 exon 4 p.Leu166Profs*7 (c.497_498del): This variant has been reported in the literature in at least 4 individuals with Transcobalamin II Deficiency; 3 of these individuals were homozygous, 1 was a compound heterozygote who was identified to have an additional likely disease causing variant in the TCN2 gene (Schiff 2010 PMID:20352340, Trakadis 2014 PMID:24305960). This variant is present in 0.2% (7/24962) of African alleles in the Genome Aggregation Database (https://gnomad.broadinstitute.org/variant/22-31010402-GTC-G). Please note, disease causing variants may be present in control databases at low frequencies, reflective of the general population, carrier status and/or variable expressivity. This variant is present in ClinVar, with several labs classifying this variant as pathogenic or Likely Pathogenic (Variation ID:376919). Evolutionary conservation and computational predictive tools for this variant are limited or unavailable. This variant is a deletion of 2 nucleotides at position 497 which results in a premature stop codon 7 amino acids downstream from this location which is predicted to result in an absent or abnormal protein. Loss of function variants are a known mechanism of disease for this gene (Li 1994 PMID:7980584). In summary, this variant is classified as pathogenic. -

Oct 19, 2018

Illumina Laboratory Services, Illumina

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The TCN2 c.497_498delTC (p.Leu166ProfsTer7) variant results in a frameshift and is predicted to result in premature termination of the protein. The p.Leu166ProfsTer7 variant has been reported in two studies and is found in a total of four unrelated individuals with transcobalamin II deficiency, including in three in a homozygous state and in one in a compound heterozygous state (Schiff et al. 2010; Trakadis et al. 2014). Control data are unavailable for this variant, which is reported at a frequency of 0.00048 in the African population of the Exome Aggregation Consortium. Based on the evidence and the potential impact of frameshift variants, the p.Leu166ProfsTer7 variant is classified as likely pathogenic for transcobalamin II deficiency. This variant was observed by ICSL as part of a predisposition screen in an ostensibly healthy population. -

Jan 06, 2025

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This sequence change creates a premature translational stop signal (p.Leu166Profs*7) in the TCN2 gene. It is expected to result in an absent or disrupted protein product. Loss-of-function variants in TCN2 are known to be pathogenic (PMID: 7980584, 20352340). This variant is present in population databases (rs778381859, gnomAD 0.03%). This premature translational stop signal has been observed in individuals with transcobalamin deficiency (PMID: 20352340). For these reasons, this variant has been classified as Pathogenic. -

Inborn genetic diseases Uncertain:1

Feb 05, 2015

Ambry Genetics

Significance: Uncertain significance

Review Status: flagged submission

Collection Method: clinical testing

Lines of evidence used in support of classification: POSITIVE: Relevant Alteration(s) Detected -

Computational scores

Source: dbNSFP v4.3

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: rs778381859; hg19: chr22-31010402;