14-88824730-T-A

Variant summary

Our verdict is Uncertain significance. Variant got 3 ACMG points: 3P and 0B. PM2 PP3

The NM_144596.4(TTC8):c.23T>A(p.Leu8Gln) variant causes a missense change. The variant allele was found at a frequency of 0.00000248 in 1,610,732 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Uncertain significance (★). Synonymous variant affecting the same amino acid position (i.e. L8L) has been classified as Likely benign.

• Frequency:
  • Genomes: 𝑓 0.000020 (0 hom., cov: 32)
  • Exomes 𝑓: 6.9e-7 (0 hom.)
• Consequence: TTC8 NM_144596.4 missense
• Clinical Significance: Uncertain significance criteria provided, single submitter U:1
• Conservation: PhyloP100: 5.54

Genes affected

TTC8 (HGNC:20087): (tetratricopeptide repeat domain 8) This gene encodes a protein that has been directly linked to Bardet-Biedl syndrome. The primary features of this syndrome include retinal dystrophy, obesity, polydactyly, renal abnormalities and learning disabilities. Experimentation in non-human eukaryotes suggests that this gene is expressed in ciliated cells and that it is involved in the formation of cilia. A mutation in this gene has also been implicated in nonsyndromic retinitis pigmentosa. Alternative splicing results in multiple transcript variants. [provided by RefSeq, Jan 2014]

ACMG classification

Verdict is Uncertain_significance. Variant got 3 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.815

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
TTC8	NM_144596.4	c.23T>A	p.Leu8Gln	missense_variant	1/15	ENST00000380656.7

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
TTC8	ENST00000380656.7	c.23T>A	p.Leu8Gln	missense_variant	1/15	2	NM_144596.4

Frequencies

GnomAD3 genomes AF: 0.0000197 AC: 3 AN: 152098 Hom.: 0 Cov.: 32

Gnomad AFR AF: 0.00

Gnomad AMI AF: 0.00

Gnomad AMR AF: 0.00

Gnomad ASJ AF: 0.00

Gnomad EAS AF: 0.000581

Gnomad SAS AF: 0.00

Gnomad FIN AF: 0.00

Gnomad MID AF: 0.00

Gnomad NFE AF: 0.00

Gnomad OTH AF: 0.00

GnomAD4 exome AF: 6.86e-7 AC: 1 AN: 1458634 Hom.: 0 Cov.: 31 AF XY: 0.00 AC XY: 0 AN XY: 725290

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.00

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.0000252

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.00

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome AF: 0.0000197 AC: 3 AN: 152098 Hom.: 0 Cov.: 32 AF XY: 0.0000404 AC XY: 3 AN XY: 74298

Gnomad4 AFR AF: 0.00

Gnomad4 AMR AF: 0.00

Gnomad4 ASJ AF: 0.00

Gnomad4 EAS AF: 0.000581

Gnomad4 SAS AF: 0.00

Gnomad4 FIN AF: 0.00

Gnomad4 NFE AF: 0.00

Gnomad4 OTH AF: 0.00

Bravo AF: 0.00000378

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:1

Revision: criteria provided, single submitter

Submissions by phenotype

Bardet-Biedl syndrome Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Invitae

Nov 15, 2022

This variant has not been reported in the literature in individuals affected with TTC8-related conditions. 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. Advanced modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) has been performed at Invitae for this missense variant, however the output from this modeling did not meet the statistical confidence thresholds required to predict the impact of this variant on TTC8 protein function. ClinVar contains an entry for this variant (Variation ID: 1471826). This variant is present in population databases (no rsID available, gnomAD 0.1%). This sequence change replaces leucine, which is neutral and non-polar, with glutamine, which is neutral and polar, at codon 8 of the TTC8 protein (p.Leu8Gln). -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.30	D
BayesDel_noAF	Pathogenic	0.19
Cadd	Pathogenic	28
Dann	Uncertain	1.0
DEOGEN2	Benign	0.25	T;T;.;.;T;T;.;.;.
Eigen	Pathogenic	0.75
Eigen_PC	Pathogenic	0.72
FATHMM_MKL	Uncertain	0.90	D
LIST_S2	Pathogenic	0.98	D;D;D;D;.;.;D;.;D
M_CAP	Uncertain	0.22	D
MetaRNN	Pathogenic	0.81	D;D;D;D;D;D;D;D;D
MetaSVM	Uncertain	0.57	D
MutationTaster	Benign	1.0	D;D;D;D;D;D
PrimateAI	Uncertain	0.62	T
Sift4G	Uncertain	0.022	D;D;D;D;D;D;T;D;D
Polyphen		0.98, 1.0	.;.;D;.;.;.;D;D;D
Vest4		0.79
MutPred		0.50		Gain of helix (P = 0.0034);Gain of helix (P = 0.0034);Gain of helix (P = 0.0034);Gain of helix (P = 0.0034);Gain of helix (P = 0.0034);Gain of helix (P = 0.0034);Gain of helix (P = 0.0034);Gain of helix (P = 0.0034);Gain of helix (P = 0.0034);
MVP		0.99
MPC		0.54
ClinPred		0.99	D
GERP RS		5.5
RBP_binding_hub_radar		0.0
RBP_regulation_power_radar		2.0
gMVP		0.67

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: rs1277993132; hg19: chr14-89291074;