14-88841177-G-T

Variant names:

• chr14-88841177-G-T
• rs754686957
• NM_144596.4:c.470G>T

Variant summary

Our verdict is Uncertain significance. The variant received 4 ACMG points: 4P and 0B. PM2 PP3_Moderate

The NM_144596.4(TTC8):​c.470G>T​(p.Arg157Ile) variant causes a missense change involving the alteration of a conserved nucleotide. The variant allele was found at a frequency of 0.000000684 in 1,461,782 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. No clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar. Another variant affecting the same amino acid position, but resulting in a different missense (i.e. R157K) has been classified as Uncertain significance.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 6.8e-7 (0 hom.)
• Consequence: TTC8 NM_144596.4 missense
• Clinical Significance: Not reported in ClinVar
• Conservation: PhyloP100: 9.87
• Publications: 1 publications found

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]

TTC8 Gene-Disease associations (from GenCC):

• Bardet-Biedl syndrome 8

  Inheritance: AR Classification: DEFINITIVE, STRONG, MODERATE Submitted by: Genomics England PanelApp, Ambry Genetics, Labcorp Genetics (formerly Invitae), G2P
• retinitis pigmentosa 51

  Inheritance: AR Classification: DEFINITIVE, STRONG Submitted by: Labcorp Genetics (formerly Invitae), G2P
• retinitis pigmentosa

  Inheritance: AD Classification: SUPPORTIVE Submitted by: Orphanet
• Bardet-Biedl syndrome

  Inheritance: AR Classification: SUPPORTIVE Submitted by: Orphanet

ACMG classification

Our verdict: Uncertain_significance. The variant received 4 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.882

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
TTC8	NM_144596.4	c.470G>T	p.Arg157Ile	missense_variant	Exon 5 of 15	ENST00000380656.7	NP_653197.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
TTC8	ENST00000380656.7	c.470G>T	p.Arg157Ile	missense_variant	Exon 5 of 15	2	NM_144596.4	ENSP00000370031.2

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD2 exomes AF: 0.00000399 AC: 1 AN: 250888 AF XY: 0.00000737

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: 6.84e-7 AC: 1 AN: 1461782 Hom.: 0 Cov.: 33 AF XY: 0.00000138 AC XY: 1 AN XY: 727182

⚠️ 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: 33472

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

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 26132

East Asian (EAS) AF: 0.00 AC: 0 AN: 39696

South Asian (SAS) AF: 0.0000116 AC: 1 AN: 86254

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53406

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

European-Non Finnish (NFE) AF: 0.00 AC: 0 AN: 1111976

Other (OTH) AF: 0.00 AC: 0 AN: 60386

⚠️ 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

ExAC AF: 0.00000824 AC: 1

ClinVar

Not reported in ClinVar

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Uncertain	0.48
BayesDel_addAF	Pathogenic	0.33	D
BayesDel_noAF	Pathogenic	0.33
CADD	Pathogenic	31
DANN	Uncertain	0.99
DEOGEN2	Benign	0.34	T;T;.;.;T;T;.;.
Eigen	Pathogenic	0.95
Eigen_PC	Pathogenic	0.91
FATHMM_MKL	Pathogenic	0.99	D
LIST_S2	Benign	0.83	T;D;D;D;.;.;.;D
M_CAP	Uncertain	0.12	D
MetaRNN	Pathogenic	0.88	D;D;D;D;D;D;D;D
MetaSVM	Uncertain	0.76	D
MutationAssessor	Benign	1.9	.;.;L;.;.;.;L;.
PhyloP100		9.9
PrimateAI	Uncertain	0.61	T
PROVEAN	Pathogenic	-7.4	.;.;.;.;D;D;D;D
REVEL	Pathogenic	0.85
Sift	Pathogenic	0.0	.;.;.;.;D;D;D;D
Sift4G	Pathogenic	0.0010	D;D;D;D;D;D;D;D
Polyphen		0.99, 1.0	.;.;D;.;.;.;D;D
Vest4		0.82
MutPred		0.68		.;.;Loss of MoRF binding (P = 0.0131);.;.;.;Loss of MoRF binding (P = 0.0131);.;
MVP		0.99
MPC		0.70
ClinPred		0.99	D
GERP RS		5.6
gMVP		0.83
Mutation Taster		=9/91	disease causing

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: rs754686957; hg19: chr14-89307521;