rs587777875

Positions:

• chr1-11999054-C-T

Variant summary

Our verdict is Pathogenic. Variant got 19 ACMG points: 19P and 0B. PM1 PM2 PM5 PP2 PP3_Strong PP5_Very_Strong

The NM_014874.4(MFN2):​c.775C>T​(p.Arg259Cys) variant causes a missense change involving the alteration of a conserved nucleotide. The variant allele was found at a frequency of 0.00000137 in 1,461,886 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. 13/21 in silico tools predict a damaging outcome for this variant. Variant has been reported in ClinVar as Likely pathogenic (★★). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. R259H) has been classified as Likely pathogenic.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000014 (0 hom.)
• Consequence: MFN2 NM_014874.4 missense
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:8 U:1
• Conservation: PhyloP100: 7.57

Genes affected

MFN2 (HGNC:16877): (mitofusin 2) This gene encodes a mitochondrial membrane protein that participates in mitochondrial fusion and contributes to the maintenance and operation of the mitochondrial network. This protein is involved in the regulation of vascular smooth muscle cell proliferation, and it may play a role in the pathophysiology of obesity. Mutations in this gene cause Charcot-Marie-Tooth disease type 2A2, and hereditary motor and sensory neuropathy VI, which are both disorders of the peripheral nervous system. Defects in this gene have also been associated with early-onset stroke. Two transcript variants encoding the same protein have been identified. [provided by RefSeq, Jul 2008]

ACMG classification

Verdict is Pathogenic. Variant got 19 ACMG points.

• PM1: In a hotspot region, there are 2 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 0 benign, 10 uncertain in NM_014874.4
• PM2: Very rare variant in population databases, with high coverage
• PM5: Other missense variant is known to change same aminoacid residue: Variant chr1-11999055-G-T is described in ClinVar as [Pathogenic]. Clinvar id is 637279.Status of the report is criteria_provided_single_submitter, 1 stars.
• PP2: Missense variant in gene, where missense usually causes diseases (based on misZ statistic), MFN2. . Gene score misZ 1.6575 (greater than the threshold 3.09). Trascript score misZ 3.2174 (greater than threshold 3.09). GenCC has associacion of gene with Charcot-Marie-Tooth disease type 2A2, axonal hereditary motor and sensory neuropathy, hereditary motor and sensory neuropathy type 6, Charcot-Marie-Tooth disease, axonal, autosomal recessive, type 2a2b;, multiple symmetric lipomatosis, severe early-onset axonal neuropathy due to MFN2 deficiency.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.956
• PP5: Variant 1-11999054-C-T is Pathogenic according to our data. Variant chr1-11999054-C-T is described in ClinVar as [Likely_pathogenic]. Clinvar id is 155730.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
MFN2	NM_014874.4	c.775C>T	p.Arg259Cys	missense_variant	8/19	ENST00000235329.10

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
MFN2	ENST00000235329.10	c.775C>T	p.Arg259Cys	missense_variant	8/19	1	NM_014874.4	P1

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 0.00000137 AC: 2 AN: 1461886 Hom.: 0 Cov.: 32 AF XY: 0.00000138 AC XY: 1 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: 0.00

Gnomad4 OTH exome AF: 0.0000331

GnomAD4 genome Cov.: 32

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:8 Uncertain:1

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

not provided Pathogenic:3

Pathogenic, criteria provided, single submitter	clinical testing	CeGaT Center for Human Genetics Tuebingen	Apr 01, 2023	MFN2: PM1, PM2, PM5, PS2:Moderate, PP2, PP3, PP4 -
Likely pathogenic, criteria provided, single submitter	clinical testing	Athena Diagnostics	Feb 16, 2017	- -
Likely pathogenic, criteria provided, single submitter	clinical testing	GeneDx	Nov 28, 2017	A variant that is likely pathogenic has been identified in the MFN2 gene. The R259C variant has been previously reported in multiple individuals with CMT2A (Sitarz et al., 2012; Drew et al., 2015; Leonardi et al., 2015). TheR259C variant is not observed in large population cohorts (Lek et al., 2016). The R259C variant is anon-conservative amino acid substitution, which is likely to impact secondary protein structure as these residues differ in polarity, charge, size and/or other properties. In-silico analyses, including protein predictors and evolutionary conservation, support a deleterious effect. Additionally, missense variants in a nearby residue (S263P) and at the sameresidue (R259L/H) have been reported in the Human Gene Mutation Database in association with MFN2-related neuropathy (Stenson et al., 2014), supporting the functional importance of this region of the protein. Therefore, this variant is likely pathogenic; however, the possibility that it is benign cannot be excluded. -

Charcot-Marie-Tooth disease type 2A2 Pathogenic:2

Pathogenic, no assertion criteria provided	literature only	Northcott Neuroscience Laboratory, ANZAC Research Institute	-	- -
Pathogenic, criteria provided, single submitter	research	Neurogenomics Lab, Neuroscience Institute, University Of Cape Town	May 22, 2024	PM2_supporting: The highest population allele frequency in gnomAD v4.0. is 0.00003311(0.003%; 2/60396 alleles in Remaining populations). PM1 met: variant occurs in the dynamin-like GTPase domain together with other pathogenic variants. PS4 met: variant identified in =10 unrelated probands with consistent phenotype for disorder. PP3_strong: Revel score is 0.95. PM5 met: MFN2 p.Arg259Leu classified as LP. PP1 not met: variant segregates with 2 informative meioses in 1 family (PMID 25802885). -

Charcot-Marie-Tooth disease Pathogenic:1 Uncertain:1

Uncertain significance, no assertion criteria provided	literature only	Inherited Neuropathy Consortium	-	- -
Likely pathogenic, criteria provided, single submitter	clinical testing	Molecular Genetics Laboratory, London Health Sciences Centre	-	- -

Inborn genetic diseases Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Ambry Genetics

May 12, 2022

The p.R259C variant (also known as c.775C>T), located in coding exon 6 of the MFN2 gene, results from a C to T substitution at nucleotide position 775. The arginine at codon 259 is replaced by cysteine, an amino acid with highly dissimilar properties. This variant has been detected in the heterozygous state in multiple patients with Charcot-Marie-Tooth Type 2A (CMT2A) disease (Sitarz KS et al. Brain, 2012 Aug;135:e219, 1-3; author reply e220, 1-3; Bombelli F et al. JAMA Neurol, 2014 Aug;71:1036-42; Drew AP et al. Mol Genet Genomic Med, 2015 Mar;3:143-54; Volodarsky M et al. J Med Genet, 2021 04;58:284-288; Ma Y et al. Front Neurol, 2021 Oct;12:757518; Wu R et al. Front Neurosci, 2021 Jul;15:705277). This variant was detected de novo in the heterozygous state in a patient with CMT2A (Felice KJ et al. Muscle Nerve, 2021 10;64:454-461). This amino acid position is highly conserved in available vertebrate species. In addition, this alteration is predicted to be deleterious by in silico analysis. Based on the supporting evidence, this variant is expected to be causative of autosomal dominant CMT2A; however, its clinical significance for autosomal recessive Charcot-Marie-Tooth disease, axonal, type 2A2B is unclear. -

Charcot-Marie-Tooth disease type 2 Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

May 13, 2023

For these reasons, this variant has been classified as Pathogenic. This variant disrupts the p.Arg259 amino acid residue in MFN2. Other variant(s) that disrupt this residue have been determined to be pathogenic (PMID: 19350291, 24627108, 24863639). This suggests that this residue is clinically significant, and that variants that disrupt this residue are likely to be disease-causing. 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) performed at Invitae indicates that this missense variant is expected to disrupt MFN2 protein function. ClinVar contains an entry for this variant (Variation ID: 155730). This missense change has been observed in individuals with autosomal dominant Charcot-Marie-Tooth disease (PMID: 22492563, 24957169, 25802885, 25957633). This variant is not present in population databases (gnomAD no frequency). This sequence change replaces arginine, which is basic and polar, with cysteine, which is neutral and slightly polar, at codon 259 of the MFN2 protein (p.Arg259Cys). -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.96
BayesDel_addAF	Pathogenic	0.55	D
BayesDel_noAF	Pathogenic	0.55
CADD	Pathogenic	34
DANN	Pathogenic	1.0
DEOGEN2	Pathogenic	0.91	D;D
Eigen	Pathogenic	0.92
Eigen_PC	Pathogenic	0.88
FATHMM_MKL	Uncertain	0.96	D
LIST_S2	Pathogenic	0.99	D;.
M_CAP	Pathogenic	0.44	D
MetaRNN	Pathogenic	0.96	D;D
MetaSVM	Pathogenic	1.1	D
MutationAssessor	Pathogenic	3.2	M;M
MutationTaster	Benign	1.0	D;D;D
PrimateAI	Pathogenic	0.93	D
PROVEAN	Pathogenic	-7.1	D;D
REVEL	Pathogenic	0.95
Sift	Pathogenic	0.0	D;D
Sift4G	Pathogenic	0.0	D;D
Polyphen		1.0	D;D
Vest4		0.96
MutPred		0.78		Loss of MoRF binding (P = 0.0187);Loss of MoRF binding (P = 0.0187);
MVP		0.98
MPC		2.1
ClinPred		1.0	D
GERP RS		5.6
RBP_binding_hub_radar		0.0
RBP_regulation_power_radar		1.7
Varity_R		0.87
gMVP		0.98

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.050		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: rs587777875; hg19: chr1-12059111; COSMIC: COSV52426484;