6-25081259-C-G

Variant names:

• chr6-25081259-C-G
• rs159988
• ENST00000471416.2:n.927G>C

Variant summary

Our verdict is Likely benign. The variant received -2 ACMG points: 2P and 4B. PM2 BP4_Strong

The ENST00000471416.2(CMAHP):​n.927G>C variant causes a non coding transcript exon change involving the alteration of a non-conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a benign outcome for this variant. No clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar.

• Frequency: Genomes: not found (cov: 31)
• Consequence: CMAHP ENST00000471416.2 non_coding_transcript_exon
• Clinical Significance: Not reported in ClinVar
• Conservation: PhyloP100: -2.14
• Publications: 6 publications found

Genes affected

CMAHP (HGNC:):

CMAHP (HGNC:2098): (cytidine monophospho-N-acetylneuraminic acid hydroxylase, pseudogene) Sialic acids are terminal components of the carbohydrate chains of glycoconjugates involved in ligand-receptor, cell-cell, and cell-pathogen interactions. The two most common forms of sialic acid found in mammalian cells are N-acetylneuraminic acid (Neu5Ac) and its hydroxylated derivative, N-glycolylneuraminic acid (Neu5Gc). Studies of sialic acid distribution show that Neu5Gc is not detectable in normal human tissues although it was an abundant sialic acid in other mammals. Neu5Gc is, in actuality, immunogenic in humans. The absense of Neu5Gc in humans is due to a deletion within the human gene CMAH encoding cytidine monophosphate-N-acetylneuraminic acid hydroxylase, an enzyme responsible for Neu5Gc biosynthesis. Sequences encoding the mouse, pig, and chimpanzee hydroxylase enzymes were obtained by cDNA cloning and found to be highly homologous. However, the homologous human cDNA differs from these cDNAs by a 92-bp deletion in the 5' region. This deletion, corresponding to exon 6 of the mouse hydroxylase gene, causes a frameshift mutation and premature termination of the polypeptide chain in human. It seems unlikely that the truncated human hydroxylase mRNA encodes for an active enzyme explaining why Neu5Gc is undetectable in normal human tissues. Human genomic DNA also shows evidence of this deletion which does not occur in the genomes of African great apes. Nonetheless, the CMAH gene maps to 6p21.32 in humans and great apes indicating that mutation of the CMAH gene occurred following human divergence from chimpanzees and bonobos. [provided by RefSeq, Jul 2008]

ACMG classification

Our verdict: Likely_benign. The variant received -2 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• BP4: Computational evidence support a benign effect (BayesDel_noAF=-0.86).

Variant Effect in Transcripts

ACMG analysis was done for transcript: ENST00000471416.2. You can select a different transcript below to see updated ACMG assignments.

RefSeq Transcripts

Sel.	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	CMAHP	NR_002174.2		n.2276G>C		non_coding_transcript_exon	Exon 13 of 13

Ensembl Transcripts

Sel.	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	CMAHP	ENST00000471416.2	TSL:2	n.927G>C		non_coding_transcript_exon	Exon 2 of 2
	CMAHP	ENST00000643807.1		n.2640G>C		non_coding_transcript_exon	Exon 16 of 16
	CMAHP	ENST00000761678.1		n.2510G>C		non_coding_transcript_exon	Exon 15 of 15

Frequencies

GnomAD3 genomes Cov.: 31

GnomAD4 exome Cov.: 0

GnomAD4 genome Cov.: 31

ClinVar

Not reported in ClinVar

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
BayesDel_noAF	Benign	-0.86
CADD	Benign	0.0070
DANN	Benign	0.42
PhyloP100		-2.1

Splicing

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

Other links and lift over

dbSNP: rs159988; hg19: chr6-25081487;