1-161306819-C-A

Position:

• chr1-161306819-C-A

Variant summary

Our verdict is Uncertain significance. Variant got 5 ACMG points: 5P and 0B. PM1 PM2 PP3

The NM_000530.8(MPZ):​c.337G>T​(p.Val113Phe) variant causes a missense change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.000000684 in 1,461,884 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 (★★). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. V113I) has been classified as Benign.

• Frequency:
  • Genomes: not found (cov: 29)
  • Exomes 𝑓: 6.8e-7 (0 hom.)
• Consequence: MPZ NM_000530.8 missense
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts P:1 U:3
• Conservation: PhyloP100: 0.679

Genes affected

MPZ (HGNC:7225): (myelin protein zero) This gene is specifically expressed in Schwann cells of the peripheral nervous system and encodes a type I transmembrane glycoprotein that is a major structural protein of the peripheral myelin sheath. The encoded protein contains a large hydrophobic extracellular domain and a smaller basic intracellular domain, which are essential for the formation and stabilization of the multilamellar structure of the compact myelin. Mutations in this gene are associated with autosomal dominant form of Charcot-Marie-Tooth disease type 1 (CMT1B) and other polyneuropathies, such as Dejerine-Sottas syndrome (DSS) and congenital hypomyelinating neuropathy (CHN). A recent study showed that two isoforms are produced from the same mRNA by use of alternative in-frame translation termination codons via a stop codon readthrough mechanism. [provided by RefSeq, Oct 2015]

ACMG classification

Verdict is Uncertain_significance. Variant got 5 ACMG points.

• PM1: In a disulfide_bond (size 77) in uniprot entity MYP0_HUMAN there are 81 pathogenic changes around while only 1 benign (99%) in NM_000530.8
• PM2: Very rare variant in population databases, with high coverage
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.765

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
MPZ	NM_000530.8	c.337G>T	p.Val113Phe	missense_variant	3/6	ENST00000533357.5	NP_000521.2
MPZ	NM_001315491.2	c.337G>T	p.Val113Phe	missense_variant	3/6		NP_001302420.1
MPZ	XM_017001321.3	c.367G>T	p.Val123Phe	missense_variant	3/6		XP_016856810.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
MPZ	ENST00000533357.5	c.337G>T	p.Val113Phe	missense_variant	3/6	1	NM_000530.8	ENSP00000432943	P1

Frequencies

GnomAD3 genomes Cov.: 29

GnomAD4 exome AF: 6.84e-7 AC: 1 AN: 1461884 Hom.: 0 Cov.: 34 AF XY: 0.00 AC XY: 0 AN XY: 727246

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.00

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: 8.99e-7

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 29

ClinVar

Significance: Uncertain significance

Submissions summary: Pathogenic:1 Uncertain:3

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Charcot-Marie-Tooth disease type 1B Pathogenic:1

Pathogenic, no assertion criteria provided

literature only

GeneReviews

Mar 26, 2015

- -

Charcot-Marie-Tooth disease Uncertain:1

Uncertain significance, no assertion criteria provided

literature only

Inherited Neuropathy Consortium

-

- -

not provided Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

GeneDx

May 29, 2018

A variant of uncertain significance has been identified in the MPZ gene. The V113F variant has been previously reported in an individual with demyelinating and axonal peripheral neuropathy, pes cavus, and pupillary light-near dissociation (Bienfait et al., 2002). However, this individual was also found to carry another variant (H81Y) on the same allele and parental studies were not performed. The V113F variant is not observed in large population cohorts (Lek et al., 2016). The V113F variant is a semi-conservative amino acid substitution, which may impact secondary protein structure as these residues differ in some properties. Missense variants in nearby residues have been reported in the Human Gene Mutation Database in individuals with MPZ-related disorders (Stenson et al., 2014). However, in-silico analyses, including protein predictors and evolutionary conservation, support that this variant does not alter protein structure/function. Therefore, based on the currently available information, it is unclear whether this variant is a pathogenic variant or a rare benign variant. -

Charcot-Marie-Tooth disease, type I Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Aug 20, 2019

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. 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: "Probably Damaging"; Align-GVGD: "Class C0"). This variant has been observed on the same chromosome (in cis) as another MPZ variant in an individual affected with peripheral neuropathy with demyelinating and axonal features (PMID: 11801400). ClinVar contains an entry for this variant (Variation ID: 41020, 208147). This variant is not present in population databases (ExAC no frequency). This sequence change replaces valine with phenylalanine at codon 113 of the MPZ protein (p.Val113Phe). The valine residue is highly conserved and there is a small physicochemical difference between valine and phenylalanine. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Uncertain	0.40
BayesDel_addAF	Pathogenic	0.18	D
BayesDel_noAF	Uncertain	0.020
CADD	Uncertain	25
DANN	Uncertain	0.99
DEOGEN2	Benign	0.32	T
Eigen	Uncertain	0.25
Eigen_PC	Uncertain	0.23
FATHMM_MKL	Benign	0.73	D
LIST_S2	Uncertain	0.89	D
M_CAP	Benign	0.030	D
MetaRNN	Pathogenic	0.77	D
MetaSVM	Benign	-0.79	T
MutationAssessor	Benign	1.8	L
MutationTaster	Benign	1.0	D;D;D;D
PrimateAI	Uncertain	0.55	T
PROVEAN	Benign	-2.0	N
REVEL	Uncertain	0.31
Sift	Benign	0.41	T
Sift4G	Benign	0.69	T
Polyphen		1.0	D
Vest4		0.76
MutPred		0.44		Loss of ubiquitination at K108 (P = 0.1264);
MVP		0.97
MPC		1.6
ClinPred		0.86	D
GERP RS		3.9
Varity_R		0.69
gMVP		0.97

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.010		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: rs281865126; hg19: chr1-161276609;