rs1553508246

Variant names:

• chr2-165898769-T-C
• rs1553508246
• NM_024753.5:c.2869-2A>G

Variant summary

Our verdict is Likely pathogenic. The variant received 6 ACMG points: 6P and 0B. PVS1_Moderate PM2 PP5_Moderate

The NM_024753.5(TTC21B):​c.2869-2A>G variant causes a splice acceptor, intron change involving the alteration of a conserved nucleotide. The variant allele was found at a frequency of 0.000000688 in 1,453,046 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. 3/3 splice prediction tools predicting alterations to normal splicing. Variant has been reported in ClinVar as Likely pathogenic (★).

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 6.9e-7 (0 hom.)
• Consequence: TTC21B NM_024753.5 splice_acceptor, intron
• Scores: Splicing: ADA: 1.000
• Clinical Significance: Likely pathogenic criteria provided, single submitter P:1
• Conservation: PhyloP100: 7.58
• Publications: 0 publications found

Genes affected

TTC21B (HGNC:25660): (tetratricopeptide repeat domain 21B) This gene encodes a member of TTC21 family, containing several tetratricopeptide repeat (TPR) domains. This protein is localized to the cilium axoneme, and may play a role in retrograde intraflagellar transport in cilia. Mutations in this gene are associated with various ciliopathies, nephronophthisis 12, and asphyxiating thoracic dystrophy 4. [provided by RefSeq, Oct 2011]

TTC21B Gene-Disease associations (from GenCC):

• nephronophthisis 12

  Inheritance: AD, AR Classification: DEFINITIVE, STRONG, LIMITED Submitted by: Ambry Genetics, ClinGen, Labcorp Genetics (formerly Invitae)
• asphyxiating thoracic dystrophy 4

  Inheritance: AR Classification: DEFINITIVE, STRONG Submitted by: Ambry Genetics, Labcorp Genetics (formerly Invitae)
• Jeune syndrome

  Inheritance: AR Classification: SUPPORTIVE Submitted by: Orphanet
• nephronophthisis 2

  Inheritance: AR Classification: SUPPORTIVE Submitted by: Orphanet

ACMG classification

Our verdict: Likely_pathogenic. The variant received 6 ACMG points.

• PVS1: Splicing +-2 bp (donor or acceptor) variant, product NOT destroyed by NMD, known LOF gene, truncates exone, which is 0.020754239 fraction of the gene. Cryptic splice site detected, with MaxEntScore 3, offset of -21, new splice context is: atacatggcaatatttttAGaac. Cryptic site results in inframe change. If cryptic site found is not functional and variant results in exon loss, it results in frameshift change.
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 2-165898769-T-C is Pathogenic according to our data. Variant chr2-165898769-T-C is described in ClinVar as Likely_pathogenic. ClinVar VariationId is 528907.Status of the report is criteria_provided_single_submitter, 1 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
TTC21B	NM_024753.5	c.2869-2A>G		splice_acceptor_variant, intron_variant	Intron 21 of 28	ENST00000243344.8	NP_079029.3

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
TTC21B	ENST00000243344.8	c.2869-2A>G		splice_acceptor_variant, intron_variant	Intron 21 of 28	1	NM_024753.5	ENSP00000243344.7

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 6.88e-7 AC: 1 AN: 1453046 Hom.: 0 Cov.: 28 AF XY: 0.00000138 AC XY: 1 AN XY: 723626

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

African (AFR) AF: 0.00 AC: 0 AN: 33304

American (AMR) AF: 0.00 AC: 0 AN: 44692

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 26088

East Asian (EAS) AF: 0.00 AC: 0 AN: 39608

South Asian (SAS) AF: 0.0000116 AC: 1 AN: 86112

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53274

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 5722

European-Non Finnish (NFE) AF: 0.00 AC: 0 AN: 1104136

Other (OTH) AF: 0.00 AC: 0 AN: 60110

⚠️ The allele balance in gnomAD4 Exomes is highly skewed from 0.5 (p-value = 0), which strongly suggests a high chance of mosaicism in these individuals.

GnomAD4 genome Cov.: 32

Alfa AF: 0.00 Hom.: 0

Bravo AF: 0.00000378

ClinVar

Significance: Likely pathogenic

Submissions summary: Pathogenic:1

Revision: criteria provided, single submitter

Submissions by phenotype

Jeune thoracic dystrophy;C0687120:Nephronophthisis Pathogenic:1

Jul 14, 2023

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may disrupt the consensus splice site. ClinVar contains an entry for this variant (Variation ID: 528907). This variant has not been reported in the literature in individuals affected with TTC21B-related conditions. This variant is not present in population databases (gnomAD no frequency). This sequence change affects an acceptor splice site in intron 21 of the TTC21B gene. It is expected to disrupt RNA splicing. Variants that disrupt the donor or acceptor splice site typically lead to a loss of protein function (PMID: 16199547), and loss-of-function variants in TTC21B are known to be pathogenic (PMID: 18327258, 21068128, 21258341, 23559409, 24876116, 25492405, 27491411, 29068549). In summary, the currently available evidence indicates that the variant is pathogenic, but additional data are needed to prove that conclusively. Therefore, this variant has been classified as Likely Pathogenic. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.63	D
BayesDel_noAF	Pathogenic	0.36
CADD	Pathogenic	30
DANN	Uncertain	0.99
Eigen	Pathogenic	1.1
Eigen_PC	Pathogenic	1.0
FATHMM_MKL	Pathogenic	0.99	D
PhyloP100		7.6
GERP RS		5.8
RBP_binding_hub_radar		0.0
RBP_regulation_power_radar		1.1
Mutation Taster		=1/99	disease causing (ClinVar)

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Pathogenic	1.0
dbscSNV1_RF	Pathogenic	0.93
SpliceAI score (max)		0.99		Details are displayed if max score is > 0.2
DS_AL_spliceai		0.99		Position offset: -2

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

Other links and lift over

dbSNP: rs1553508246; hg19: chr2-166755279;