Intellectual disability
Gene: SHMT2

SHMT2 (serine hydroxymethyltransferase 2)
EnsemblGeneIds (GRCh38): ENSG00000182199
EnsemblGeneIds (GRCh37): ENSG00000182199
OMIM: 138450, Gene2Phenotype
SHMT2 is in 5 panels

3 reviews

Sarah Leigh (Genomics England Curator)

The rating of this gene has been updated following NHS Genomic Medicine Service approval.
Created: 9 Mar 2022, 3:40 p.m. | Last Modified: 9 Mar 2022, 3:40 p.m.

Panel Version: 3.1510

Created: 9 Mar 2022, 3:40 p.m.
Last Modified: 9 Mar 2022, 3:40 p.m.
Panel version: 3.1510

Arina Puzriakova (Genomics England Curator)

Comment on list classification: New gene added by Konstantinos Varvagiannis. Sufficient number of unrelated cases (>3) with ID of relevant severity to this panel. Some functional data indicating variants result in impaired SHMT2 enzymatic function. Rating Amber but should be promoted to Green at the next GMS panel update (added 'for-review' tag)

SHMT2 is listed in Gene2Phenotype with a 'probable' disease confidence rating for 'SHMT2-related neurodevelopmental syndrome', and is also associated with 'Neurodevelopmental disorder with cardiomyopathy, spasticity, and brain abnormalities, MIM# 619121' in OMIM.
Created: 21 Dec 2020, 11:18 a.m. | Last Modified: 21 Dec 2020, 11:18 a.m.

Panel Version: 3.665

Created: 21 Dec 2020, 11:18 a.m.
Last Modified: 21 Dec 2020, 11:18 a.m.
Panel version: 3.665

Konstantinos Varvagiannis (Other)

Green List (high evidence)

García‑Cazorla et al. (2020 - PMID: 33015733) report 5 individuals (from 4 families) with a novel brain and heart developmental syndrome caused by biallelic SHMT2 pathogenic variants.

All affected subjects presented similar phenotype incl. microcephaly at birth (5/5 OFC < -2 SD though in 2/5 cases N OFC was observed later), DD and ID (1/5 mild-moderate, 1/5 moderate, 3/5 severe), motor dysfunction in the form of spastic (5/5) paraparesis, ataxia/dysmetria (3/4), intention tremor (in 3/?) and/or peripheral neuropathy (2 sibs). They exhibited corpus callosum hypoplasia (5/5) and perisylvian microgyria-like pattern (4/5). Cardiac problems were reported in all, with hypertrophic cardiomyopathy in 4/5 (from 3 families) and atrial-SD in the 5th individual (1/5). Common dysmorphic features incl. long palpebral/fissures, eversion of lateral third of lower eylids, arched eyebrows, long eyelashes, thin upper lip, short Vth finger, fetal pads, mild 2-3 toe syndactyly, proximally placed thumbs.

Biallelic variants were identified following exome sequencing in all (other investigations not mentioned). Identified variants were in all cases missense SNVs or in-frame del, which together with evidence from population databases and mouse model might suggest a hypomorphic effect of variants and intolerance/embryonic lethality for homozygous LoF ones.

SHMT2 encodes the mitohondrial form of serine hydroxymethyltransferase. The enzyme transfers one-carbon units from serine to tetrahydrofolate (THF) and generates glycine and 5,10,methylene-THF.

Mitochondrial defect was suggested by presence of ragged red fibers in myocardial biopsy of one patient. Quadriceps and myocardial biopsies of the same individual were overall suggestive of myopathic changes.

While plasma metabolites were within N range and SHMT2 protein levels not significantly altered in patient fibroblasts, the authors provide evidence for impaired enzymatic function eg. presence of the SHMT2 substrate (THF) in patient but not control (mitochondria-enriched) fibroblasts , decrease in glycine/serine ratios, impared folate metabolism. Patient fibroblasts displayed impaired oxidative capacity (reduced ATP levels in a medium without glucose, diminished oxygen consumption rates). Mitochondrial membrane potential and ROS levels were also suggestive of redox malfunction.

Shmt2 ko in mice was previously shown to be embryonically lethal attributed to severe mitochondrial respiration defects, although there was no observed brain metabolic defect.

The authors performed Shmt2 knockdown in motoneurons in Drosophila, demonstrating neuromuscular junction (# of satellite boutons) and motility defects (climbing distance/velocity).

Overall this gene can be considered for inclusion with (probably) green rating in gene panels for ID, metabolic / mitochondrial disorders, cardiomyopathy, congenital microcephaly, corpus callosum anomalies, etc.
Sources: Literature
Created: 10 Oct 2020, 9:56 p.m.

Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal

Phenotypes
Congenital microcephaly; Infantile axial hypotonia; Spastic paraparesis; Global developmental delay; Intellectual disability; Abnormality of the corpus callosum; Abnormal cortical gyration; Hypertrophic cardiomyopathy; Abnormality of the face; Proximal placement of thumb; 2-3 toe syndactyly

Publications

33015733

Created: 10 Oct 2020, 9:56 p.m.

Panel version: 3.420

Details

Mode of Inheritance

BIALLELIC, autosomal or pseudoautosomal

Sources

Expert Review Green

Phenotypes

Neurodevelopmental disorder with cardiomyopathy, spasticity, and brain abnormalities, OMIM:619121

OMIM

138450

Clinvar variants

Variants in SHMT2

Penetrance

Complete

Publications

33015733

Panels with this gene