1-45500333-A-G

Position:

• chr1-45500333-A-G

Variant summary

Our verdict is Pathogenic. Variant got 20 ACMG points: 20P and 0B. PVS1 PS1_Moderate PM2 PP5_Very_Strong

The NM_015506.3(MMACHC):​c.1A>G​(p.Met1?) variant causes a start lost change. The variant allele was found at a frequency of 0.0000041 in 1,461,762 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 Pathogenic (★★).

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000041 (0 hom.)
• Consequence: MMACHC NM_015506.3 start_lost
• Clinical Significance: Pathogenic criteria provided, multiple submitters, no conflicts P:5
• Conservation: PhyloP100: 5.22

Genes affected

MMACHC (HGNC:24525): (metabolism of cobalamin associated C) The exact function of the protein encoded by this gene is not known, however, its C-terminal region shows similarity to TonB, a bacterial protein involved in energy transduction for cobalamin (vitamin B12) uptake. Hence, it is postulated that this protein may have a role in the binding and intracellular trafficking of cobalamin. Mutations in this gene are associated with methylmalonic aciduria and homocystinuria type cblC. [provided by RefSeq, Oct 2009]

ACMG classification

Verdict is Pathogenic. Variant got 20 ACMG points.

• PVS1: Start lost variant, no new inframe start found.
• PS1: Another start lost variant in NM_015506.3 (MMACHC) was described as [Pathogenic] in Lovd
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 1-45500333-A-G is Pathogenic according to our data. Variant chr1-45500333-A-G is described in ClinVar as [Pathogenic]. Clinvar id is 381577.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
MMACHC	NM_015506.3	c.1A>G	p.Met1?	start_lost	1/4	ENST00000401061.9	NP_056321.2
MMACHC	NM_001330540.2	c.-222A>G		5_prime_UTR_variant	1/4		NP_001317469.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
MMACHC	ENST00000401061.9	c.1A>G	p.Met1?	start_lost	1/4	2	NM_015506.3	ENSP00000383840	P1
MMACHC	ENST00000616135.1			upstream_gene_variant		2		ENSP00000478859

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD3 exomes AF: 0.00000801 AC: 2 AN: 249570 Hom.: 0 AF XY: 0.0000148 AC XY: 2 AN XY: 135394

Gnomad AFR exome AF: 0.00

Gnomad AMR exome AF: 0.0000290

Gnomad ASJ exome AF: 0.00

Gnomad EAS exome AF: 0.00

Gnomad SAS exome AF: 0.0000327

Gnomad FIN exome AF: 0.00

Gnomad NFE exome AF: 0.00

Gnomad OTH exome AF: 0.00

GnomAD4 exome AF: 0.00000410 AC: 6 AN: 1461762 Hom.: 0 Cov.: 30 AF XY: 0.00000688 AC XY: 5 AN XY: 727190

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.0000224

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.00

Gnomad4 SAS exome AF: 0.0000232

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.00000270

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 32

Bravo AF: 0.00000378

ExAC AF: 0.00000827 AC: 1

ClinVar

Significance: Pathogenic

Submissions summary: Pathogenic:5

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Cobalamin C disease Pathogenic:3

Pathogenic, criteria provided, single submitter	clinical testing	Counsyl	Mar 15, 2017	- -
Pathogenic, criteria provided, single submitter	clinical testing	Genome-Nilou Lab	Apr 11, 2023	- -
Pathogenic, criteria provided, single submitter	clinical testing	Labcorp Genetics (formerly Invitae), Labcorp	Dec 26, 2023	This sequence change affects the initiator methionine of the MMACHC mRNA. The next in-frame methionine is located at codon 58. This variant is present in population databases (rs758477536, gnomAD 0.003%). Disruption of the initiator codon has been observed in individuals with methylmalonic aciduria and homocystinuria (PMID: 16311595, 17768669, 19760748, 28693988). ClinVar contains an entry for this variant (Variation ID: 381577). For these reasons, this variant has been classified as Pathogenic. -

not provided Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

GeneDx

Aug 04, 2022

Initiation codon variant in a gene for which loss of function is a known mechanism of disease; Not observed at significant frequency in large population cohorts (gnomAD); This variant is associated with the following publications: (PMID: 19370762, 25398587, 19573432, 17768669, 30157807, 29731766, 35314707, 33691766, 32943488, 35361390, 34102818, 30863077, 22560872) -

Methylmalonic acidemia with homocystinuria cblC Pathogenic:1

Pathogenic, no assertion criteria provided

clinical testing

Natera, Inc.

Sep 16, 2020

- -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.54	D
BayesDel_noAF	Pathogenic	0.64
CADD	Uncertain	24
DANN	Uncertain	0.99
DEOGEN2	Benign	0.087	T
Eigen	Uncertain	0.60
Eigen_PC	Uncertain	0.60
FATHMM_MKL	Uncertain	0.91	D
LIST_S2	Uncertain	0.90	D
M_CAP	Pathogenic	0.98	D
MetaRNN	Pathogenic	0.99	D
MetaSVM	Pathogenic	0.99	D
MutationTaster	Benign	1.0	D
PROVEAN	Benign	-1.1	N
REVEL	Pathogenic	0.75
Sift	Pathogenic	0.0	D
Sift4G	Pathogenic	0.0	D
Polyphen		0.95	P
Vest4		0.96
MutPred		1.0		Loss of methylation at K4 (P = 0.105);
MVP		0.98
ClinPred		0.99	D
GERP RS		5.8
Varity_R		0.97
gMVP		0.63

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: rs758477536; hg19: chr1-45966005; COSMIC: COSV68984607; COSMIC: COSV68984607;