Abstract
The principal component of the protein homeostasis network is the ubiquitin-proteasome system. Ubiquitination is mediated by an enzymatic cascade involving, i.e., E3 ubiquitin ligases, many of which belong to the cullin-RING ligases family. Genetic defects in the ubiquitin-proteasome system components, including cullin-RING ligases, are known causes of neurodevelopmental disorders. Using exome sequencing to diagnose a pediatric patient with developmental delay, pyramidal signs, and limb ataxia, we identified a de novo missense variant c.376G>C; p.(Asp126His) in the FEM1C gene encoding a cullin-RING ligase substrate receptor. This variant alters a conserved amino acid located within a highly constrained coding region and is predicted as pathogenic by most in silico tools. In addition, a de novo FEM1C mutation of the same residue p.(Asp126Val) was associated with an undiagnosed developmental disorder, and the relevant variant (FEM1CAsp126Ala) was found to be functionally compromised in vitro. Our computational analysis showed that FEM1CAsp126His hampers protein substrate binding. To further assess its pathogenicity, we used the nematode Caenorhabditis elegans. We found that the FEM-1Asp133His animals (expressing variant homologous to the FEM1C p.(Asp126Val)) had normal muscle architecture yet impaired mobility. Mutant worms were sensitive to the acetylcholinesterase inhibitor aldicarb but not levamisole (acetylcholine receptor agonist), showing that their disabled locomotion is caused by synaptic abnormalities and not muscle dysfunction. In conclusion, we provide the first evidence from an animal model suggesting that a mutation in the evolutionarily conserved FEM1C Asp126 position causes a neurodevelopmental disorder in humans.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
We provided information about another reported de novo mutation in the same residue (FEM1CAsp126Val) as well as about a de novo mutation in another member of the FEM1 family, FEM1BArg126Gln, both of which are associated with syndromic intellectual disability and indicate the involvement of FEM1 receptors in the development of the nervous system. We also included a more detailed clinical description of the patient. Finally, we provided additional functional data on C. elegans and computational identification of the deleterious effect of mutations of FEM1C Asp126 residues on interactions with a specific protein substrate.
Abbreviations
- Ach
- acetylcholine
- AchE
- acetylcholinesterase
- ADHD
- attention deficit hyperactivity disorder
- ADS
- amplicon deep sequencing
- ASD
- autism spectrum disorder
- CCR
- constrained coding region
- CP
- cerebral palsy
- CRLs
- cullin-RING ligases
- DD
- developmental delay
- E1
- ubiquitin-activating enzyme
- E2
- ubiquitin-conjugating enzyme
- E3
- ubiquitin ligase
- ID
- intellectual disability
- LOF
- loss of function
- nAchR
- nicotinic acetylcholine receptor
- NDDs
- neurodevelopmental disorders
- NGM
- nematode growth medium
- MRI
- magnetic resonance imaging
- UPS
- ubiquitin-proteasome system
- RING
- Really Interesting New Gene
- RNA
- ribonucleic acid
- RNAi
- ribonucleic acid interference
- RMSD
- root-mean-square deviation
- WES
- whole exome sequencing