rs756313678

Positions:

• chr8-63061337-G-A

Variant summary

Our verdict is Uncertain significance. Variant got 4 ACMG points: 4P and 0B. PM1 PM2

The NM_000370.3(TTPA):​c.752C>T​(p.Ser251Phe) variant causes a missense change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.0000155 in 1,613,758 control chromosomes in the GnomAD database, with no homozygous occurrence. Variant has been reported in ClinVar as Uncertain significance (★★).

• Frequency:
  • Genomes: 𝑓 0.0000066 (0 hom., cov: 33)
  • Exomes 𝑓: 0.000016 (0 hom.)
• Consequence: TTPA NM_000370.3 missense
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:6
• Conservation: PhyloP100: 2.92

Genes affected

TTPA (HGNC:12404): (alpha tocopherol transfer protein) This gene encodes a soluble protein that binds alpha-trocopherol, a form of vitamin E, with high selectivity and affinity. This protein plays an important role in regulating vitamin E levels in the body by transporting vitamin E between membrane vesicles and facilitating the secretion of vitamin E from hepatocytes to circulating lipoproteins. Mutations in this gene cause hereditary vitamin E deficiency (ataxia with vitamin E deficiency, AVED) and retinitis pigmentosa. [provided by RefSeq, Nov 2009]

ACMG classification

Verdict is Uncertain_significance. Variant got 4 ACMG points.

• PM1: In a chain Alpha-tocopherol transfer protein (size 277) in uniprot entity TTPA_HUMAN there are 18 pathogenic changes around while only 3 benign (86%) in NM_000370.3
• PM2: Very rare variant in population databases, with high coverage

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
TTPA	NM_000370.3	c.752C>T	p.Ser251Phe	missense_variant	5/5	ENST00000260116.5

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
TTPA	ENST00000260116.5	c.752C>T	p.Ser251Phe	missense_variant	5/5	1	NM_000370.3	P1
TTPA	ENST00000521138.1	n.233-12734C>T		intron_variant, non_coding_transcript_variant		5

Frequencies

GnomAD3 genomes AF: 0.00000657 AC: 1 AN: 152150 Hom.: 0 Cov.: 33

Gnomad AFR AF: 0.00

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: 0.0000147

Gnomad OTH AF: 0.00

GnomAD3 exomes AF: 0.0000477 AC: 12 AN: 251322 Hom.: 0 AF XY: 0.0000442 AC XY: 6 AN XY: 135824

Gnomad AFR exome AF: 0.00

Gnomad AMR exome AF: 0.000318

Gnomad ASJ exome AF: 0.00

Gnomad EAS exome AF: 0.00

Gnomad SAS exome AF: 0.00

Gnomad FIN exome AF: 0.00

Gnomad NFE exome AF: 0.00000880

Gnomad OTH exome AF: 0.00

GnomAD4 exome AF: 0.0000164 AC: 24 AN: 1461608 Hom.: 0 Cov.: 31 AF XY: 0.0000165 AC XY: 12 AN XY: 727118

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.000358

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: 0.00000540

Gnomad4 OTH exome AF: 0.0000331

GnomAD4 genome AF: 0.00000657 AC: 1 AN: 152150 Hom.: 0 Cov.: 33 AF XY: 0.0000135 AC XY: 1 AN XY: 74318

Gnomad4 AFR AF: 0.00

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: 0.0000147

Gnomad4 OTH AF: 0.00

Alfa AF: 0.0000282 Hom.: 0

Bravo AF: 0.0000113

ExAC AF: 0.00000824 AC: 1

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:6

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

not provided Uncertain:3

Uncertain significance, criteria provided, single submitter	clinical testing	Invitae	Sep 01, 2022	This sequence change replaces serine, which is neutral and polar, with phenylalanine, which is neutral and non-polar, at codon 251 of the TTPA protein (p.Ser251Phe). This variant is present in population databases (rs756313678, gnomAD 0.03%). This variant has not been reported in the literature in individuals affected with TTPA-related conditions. ClinVar contains an entry for this variant (Variation ID: 448840). Algorithms developed to predict the effect of missense changes on protein structure and function are either unavailable or do not agree on the potential impact of this missense change (SIFT: "Deleterious"; PolyPhen-2: "Possibly Damaging"; Align-GVGD: "Class C0"). 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. -
Uncertain significance, criteria provided, single submitter	clinical testing	Athena Diagnostics	Oct 25, 2022	Available data are insufficient to determine the clinical significance of the variant at this time. The frequency of this variant in the general population is uninformative in assessment of its pathogenicity (http://gnomad.broadinstitute.org). Computational tools predict that this variant is not damaging. -
Uncertain significance, criteria provided, single submitter	clinical testing	Mayo Clinic Laboratories, Mayo Clinic	Apr 19, 2022	- -

Familial isolated deficiency of vitamin E Uncertain:2

Uncertain significance, no assertion criteria provided	clinical testing	Natera, Inc.	Nov 11, 2019	- -
Uncertain significance, criteria provided, single submitter	clinical testing	Illumina Laboratory Services, Illumina	Jan 13, 2018	This variant was observed in the ICSL laboratory as part of a predisposition screen in an ostensibly healthy population. It had not been previously curated by ICSL or reported in the Human Gene Mutation Database (HGMD: prior to June 1st, 2018), and was therefore a candidate for classification through an automated scoring system. Utilizing variant allele frequency, disease prevalence and penetrance estimates, and inheritance mode, an automated score was calculated to assess if this variant is too frequent to cause the disease. Based on the score, this variant could not be ruled out of causing disease and therefore its association with disease required further investigation. A literature search was performed for the gene, cDNA change, and amino acid change (if applicable). No publications were found based on this search. This variant was therefore classified as a variant of unknown significance for this disease. -

Inborn genetic diseases Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Ambry Genetics

Jun 11, 2024

The c.752C>T (p.S251F) alteration is located in exon 5 (coding exon 5) of the TTPA gene. This alteration results from a C to T substitution at nucleotide position 752, causing the serine (S) at amino acid position 251 to be replaced by a phenylalanine (F). Based on insufficient or conflicting evidence, the clinical significance of this alteration remains unclear. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Uncertain	0.45
BayesDel_addAF	Benign	-0.15	T
BayesDel_noAF	Benign	-0.14
CADD	Uncertain	24
DANN	Uncertain	0.99
DEOGEN2	Uncertain	0.78	D
Eigen	Uncertain	0.30
Eigen_PC	Uncertain	0.35
FATHMM_MKL	Uncertain	0.90	D
LIST_S2	Benign	0.78	T
M_CAP	Uncertain	0.088	D
MetaRNN	Uncertain	0.53	D
MetaSVM	Uncertain	0.023	D
MutationAssessor	Uncertain	2.7	M
MutationTaster	Benign	0.94	D
PrimateAI	Benign	0.48	T
PROVEAN	Uncertain	-2.7	D
REVEL	Uncertain	0.41
Sift	Uncertain	0.012	D
Sift4G	Benign	0.13	T
Polyphen		0.86	P
Vest4		0.37
MutPred		0.51		Loss of disorder (P = 0.0393);
MVP		0.91
MPC		0.45
ClinPred		0.39	T
GERP RS		4.0
Varity_R		0.55
gMVP		0.71

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: rs756313678; hg19: chr8-63973896; COSMIC: COSV99478502;