chr1-45508869-GGATAGAGGTGCCA-G

Variant names:

• chr1-45508869-GGATAGAGGTGCCA-G
• rs1553162923
• NM_015506.3:c.507_519delAGAGGTGCCAGAT

Variant summary

Our verdict is Pathogenic. The variant received 16 ACMG points: 16P and 0B. PVS1 PP5_Very_Strong

The NM_015506.3(MMACHC):​c.507_519delAGAGGTGCCAGAT​(p.Glu170CysfsTer36) variant causes a frameshift change. The variant was absent in control chromosomes in GnomAD project. It is difficult to determine the true allele frequency of this variant because it is of type DEL_BIG, and the frequency of such variant types in population databases may be underestimated and unreliable. Variant has been reported in ClinVar as Likely pathogenic (★★).

• Frequency: Genomes: not found (cov: 32)
• Consequence: MMACHC NM_015506.3 frameshift
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:5
• Conservation: PhyloP100: 6.36
• Publications: 0 publications found

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]

MMACHC Gene-Disease associations (from GenCC):

• methylmalonic aciduria and homocystinuria type cblC

  Inheritance: AR Classification: DEFINITIVE, STRONG, SUPPORTIVE Submitted by: Labcorp Genetics (formerly Invitae), Ambry Genetics, Myriad Women’s Health, ClinGen, G2P, Orphanet

ACMG classification

Our verdict: Pathogenic. The variant received 16 ACMG points.

• PVS1: Loss of function variant, product does not undergo nonsense mediated mRNA decay. Variant is located in the 3'-most exon, not predicted to undergo nonsense mediated mRNA decay. There are 54 pathogenic variants in the truncated region.
• PP5: Variant 1-45508869-GGATAGAGGTGCCA-G is Pathogenic according to our data. Variant chr1-45508869-GGATAGAGGTGCCA-G is described in ClinVar as Pathogenic/Likely_pathogenic. ClinVar VariationId is 556017.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Variant Effect in Transcripts

ACMG analysis was done for transcript: NM_015506.3. You can select a different transcript below to see updated ACMG assignments.

RefSeq Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	MMACHC	NM_015506.3	MANE Select	c.507_519delAGAGGTGCCAGAT	p.Glu170CysfsTer36	frameshift	Exon 4 of 4	NP_056321.2
	MMACHC	NM_001330540.2		c.336_348delAGAGGTGCCAGAT	p.Glu113CysfsTer36	frameshift	Exon 4 of 4	NP_001317469.1

Ensembl Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	MMACHC	ENST00000401061.9	TSL:2 MANE Select	c.507_519delAGAGGTGCCAGAT	p.Glu170CysfsTer36	frameshift	Exon 4 of 4	ENSP00000383840.4
	MMACHC	ENST00000616135.1	TSL:2	c.336_348delAGAGGTGCCAGAT	p.Glu113CysfsTer36	frameshift	Exon 4 of 5	ENSP00000478859.1

Frequencies

GnomAD3 genomes Cov.: 32

We have no GnomAD4 exomes data on this position. Probably position not covered by the project.

GnomAD4 genome Cov.: 32

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:5

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Cobalamin C disease Pathogenic:5

Apr 11, 2023

Genome-Nilou Lab

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Jan 11, 2024

Baylor Genetics

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Jan 08, 2018

Counsyl

Significance: Pathogenic

Review Status: no assertion criteria provided

Collection Method: clinical testing

This submission and the accompanying classification are no longer maintained by the submitter. For more information on current observations and classification, please contact variantquestions@myriad.com.

Feb 08, 2024

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This sequence change creates a premature translational stop signal (p.Glu170Cysfs*36) in the MMACHC gene. While this is not anticipated to result in nonsense mediated decay, it is expected to disrupt the last 113 amino acid(s) of the MMACHC protein. This variant is not present in population databases (gnomAD no frequency). This premature translational stop signal has been observed in individual(s) with combined methylmalonic acidemia and hyperhomocysteinemia (PMID: 20924684). ClinVar contains an entry for this variant (Variation ID: 556017). Experimental studies and prediction algorithms are not available or were not evaluated, and the functional significance of this variant is currently unknown. This variant disrupts a region of the MMACHC protein in which other variant(s) (p.Ile190Tyrfs*13, p.Trp203*, p.Tyr205*) have been determined to be pathogenic (PMID: 16311595, 20631720, 23954310, 27383490). This suggests that this is a clinically significant region of the protein, and that variants that disrupt it are likely to be disease-causing. For these reasons, this variant has been classified as Pathogenic.

Nov 16, 2018

Women's Health and Genetics/Laboratory Corporation of America, LabCorp

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Variant summary: MMACHC c.507_519del13 (p.Glu170CysfsX36) results in a premature termination codon, predicted to cause a truncation of the encoded protein or absence of the protein due to nonsense mediated decay, which are commonly known mechanisms for disease. Truncations downstream of this position have been classified as pathogenic by our laboratory (eg. p.Trp203X, p.Tyr205X). The variant was absent in 246244 control chromosomes. c.507_519del13 has been reported in the literature in individuals affected with Cobalamin C Disease (Methylmalonic Aciduria with Homocystinuria; Lerner-Ellis_2009, Wang_2010). These data indicate that the variant may be associated with disease. To our knowledge, no experimental evidence demonstrating an impact on protein function has been reported. One clinical diagnostic laboratory has submitted clinical-significance assessments for this variant to ClinVar after 2014 without evidence for independent evaluation. One laboratory classified the variant as pathogenic. Based on the evidence outlined above, the variant was classified as likely pathogenic.

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
PhyloP100		6.4
Mutation Taster		=2/198	disease causing (ClinVar)

Splicing

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

Other links and lift over

dbSNP: rs1553162923; hg19: chr1-45974541;