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Intellectual disability

Gene: METTL23

Green List (high evidence)

METTL23 (methyltransferase like 23)
EnsemblGeneIds (GRCh38): ENSG00000181038
EnsemblGeneIds (GRCh37): ENSG00000181038
OMIM: 615262, Gene2Phenotype
METTL23 is in 3 panels

2 reviews

Ivone Leong (Genomics England Curator)

Comment on list classification: New gene added by external expert and reviewed by curation team: Sufficient evidence has been provided by the external expert review for this gene to be rated green.
Created: 19 Feb 2019, 9:43 a.m.

Konstantinos Varvagiannis (Other)

Green List (high evidence)

Biallelic pathogenic variants in METTL23 cause Mental retardation, autosomal recessive 44 (MIM 615942).

Reiff et al. (PMID: 24501276) report on a consanguineous pedigree of Yemeni origin with 7 individuals presenting intellectual disability. Clinical details are provided for 3 subjects from one branch of the family. Findings included moderate (2/3) or severe (1/3) ID, seizures (2/3) and some common facial features. Seizures were not observed in individuals from other branch of the family. The affected individuals were homozygous for a 4-bp deletion.

Bernkopf et al. (PMID: 24626631) report on a consanguineous family from Pakistan with 2 affected sibs as well as a non-consanguineous family from Austria with 4 affected sibs. The parents in the latter family originated from a small - geographically isolated - village. Individuals from the Pakistani family were homozygous for a nonsense variant, while the sibs from the Austrian family for a frameshift variant. Mild ID was noted in all.

In total 3 different LoF variants have been reported. Extensive functional studies have been performed in both articles.

METTL23 (methyltransferase like 23) is expressed at low-to-moderate levels in the developping human brain. Bernkopf et al. suggest that METTL23 is indeed a methyltransferase.

The gene has 7 transcripts of which one is non-coding. 3 transcripts encode isoform 1 and 3 other encode isoform 2.

The variant reported by Reiff et al. affects the coding region of 3 (of the 6 coding) transcripts (corresponding to isoform 1) and the 5'-UTR of the other 3 transcripts. It is however shown that this first coding exon (specific to isoform 1) is expressed in the developing human brain, though at lower levels than downstream exons common to both isoforms. In addition, only isoform 1 appears to be conserved in most other species.

The variants described by Bernkopf et al. affect all 6 coding trancripts and as a result both isoforms. [However, the individuals reported by Bernkopf et al. were less severely affected compared to those reported by Reiff et al.]

Nonsense-mediated decay appeared unlikely since mRNA levels for both isoforms in lymphoblasts from affected individuals were similar to controls (upon qRT-PCR) [The specific nonsense variant tested would be expected to be subject to NMD given its localization].

METTL23 is not associated with any phenotype in G2P.

This gene is included in gene panels for intellectual disability offered by various diagnostic laboratories.

As a result, METTL23 can be considered for inclusion in the ID panel as green (or amber).
Sources: Literature
Created: 10 Dec 2018, 1:39 a.m.

Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal

Mental retardation, autosomal recessive 44 (MIM 615942)


Variants in this GENE are reported as part of current diagnostic practice


Mode of Inheritance
BIALLELIC, autosomal or pseudoautosomal
  • Expert Review Green
  • Mental retardation, autosomal recessive 44, 615942
Clinvar variants
Variants in METTL23
Panels with this gene

History Filter Activity

19 Feb 2019, Gel status: 3

Entity classified by Genomics England curator

Ivone Leong (Genomics England Curator)

Gene: mettl23 has been classified as Green List (High Evidence).

19 Feb 2019, Gel status: 0

Set Phenotypes

Ivone Leong (Genomics England Curator)

Phenotypes for gene: METTL23 were changed from Mental retardation, autosomal recessive 44 (MIM 615942) to Mental retardation, autosomal recessive 44, 615942

10 Dec 2018, Gel status: 0

Created, Added New Source, Set mode of inheritance, Set publications, Set Phenotypes, Set penetrance

Konstantinos Varvagiannis (Other)

gene: METTL23 was added gene: METTL23 was added to Intellectual disability. Sources: Literature Mode of inheritance for gene: METTL23 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: METTL23 were set to 24501276; 24626631 Phenotypes for gene: METTL23 were set to Mental retardation, autosomal recessive 44 (MIM 615942) Penetrance for gene: METTL23 were set to Complete Review for gene: METTL23 was set to GREEN gene: METTL23 was marked as current diagnostic