Two patients with congenital myasthenic syndrome caused by COLQ gene mutations and the consequent ColQ protein defect

Objective

To report two cases of congenital myasthenic syndromes (CMS) in a Chinese family with mutations in the COLQ gene and to prove the consequence defect of the ColQ protein.

Method

Clinical characteristics of the two children from the same family were described. Next-generation sequencing (NGS) and sanger sequencing was performed on the proband and family members. The consequence of the mutation was predicted by 3D protein structure prediction using I-TASSER. The wild type and mutant were transfected to 293T cells, and ColQ protein was detected by Western Blot.

Results

The diagnosis of CMS was based on a symptom combination of fatigable muscle weakness, ptosis, scoliosis, and hypotonia, aggravation of muscle weakness after the neostigmine test, and a 46% decrement in repetitive nerve stimulation. A muscle biopsy was performed on the proband, revealing mild variation in the myofiber size. NGS data revealed two compound heterozygous mutations at c.173delC (p.Pro58Hisfs*22) and c.C706T (p.R236X) in the COLQ gene, where the former was a novel mutation. A 3D structure prediction showed two truncated ColQ proteins with 78aa and 235aa, respectively. The truncated ColQ protein was proved in 293T cells transfected with c.173delC or c.C706T mutants by Western Blot.

Conclusions

The mutations of c.173delC and c.C706T in the COLQ gene led to truncated ColQ protein and contributed to the pathogenesis of CMS in this Chinese family.

Novel copy number variation of COLQ gene in a Moroccan patient with congenital myasthenic syndrome: a case report and review of the literature

Background

Congenital myasthenic syndromes (CMSs) are rare genetic diseases due to abnormalities of the neuromuscular junction leading to permanent or transient muscle fatigability and weakness. To date, 32 genes were found to be involved in CMSs with autosomal dominant and/or recessive inheritance patterns. CMS with acetylcholinesterase deficiency, in particular, was determined to be due to biallelic mutations of COLQ gene with early-onset clinical signs. Here, we report clinical features and novel molecular findings of COLQ-related CMS in a Moroccan patient with a review of the literature for this rare form.

Case presentation

In this study, we report the case of a 28-month-old Moroccan female patient with hypotonia, associated to axial muscle weakness, global motor delay, bilateral ptosis, unilateral partial visual field deficiency with normal ocular motility, and fatigable muscle weakness. Clinical exome sequencing revealed a novel homozygous deletion of exon 13 in COLQ gene, NM_005677.4(COLQ):c.(814+1_815-1)_(954+1_955-1) del p.(Gly272Aspfs*11). This finding was subsequently confirmed by quantitative real-time PCR (qPCR) in the proband and her parents. In silico analysis of protein-protein interaction network by STRING tool revealed that 12 proteins are highly associated to COLQ with an elevated confidence score. Treatment with Salbutamol resulted in clear benefits and recovery.

Conclusions

This clinical observation illustrates the important place of next-generation sequencing in the precise molecular diagnosis of heterogeneous forms of CMS, the appropriate management and targeted treatment, and genetic counseling of families, with a better characterization of the mutational profile of this rare disease in the Moroccan population.

Mechanisms of Congenital Myasthenia Caused by Three Mutations in the COLQ Gene

The gene encoding collagen like tail subunit of asymmetric acetylcholinesterase (COLQ) is responsible for the transcription of three strands of collagen of acetylcholinesterase, which is attached to the endplate of neuromuscular junctions. Mutations in the COLQ gene are inherited in an autosomal-recessive manner and can lead to type V congenital myasthenia syndrome (CMS), which manifests as decreased muscle strength at birth or shortly after birth, respiratory failure, restricted eye movements, drooping of eyelids, and difficulty swallowing. Here we reported three variants within COLQ in two unrelated children with CMS. An intronic variant (c.393+1G>A) and a novel missense variant (p.Q381P) were identified as compound heterozygous in a 13-month-old boy, with the parents being carriers of each. An intragenic deletion including exons 14 and 15 was found in a homozygous state in a 12-year-old boy. We studied the relative expression of the COLQ and AChE gene in the probands' families, performed three-dimensional protein structural analysis, and analyzed the conservation of the missense mutation c.1142A>C (p.Q381P). The splicing mutation c.393+1G>A was found to affect the normal splicing of COLQ exon 5, resulting in a 27-bp deletion. The missense mutation c.1142A>C (p.Q381P) was located in a conserved position in different species. We found that homozygous deletion of COLQ exons 14-15 resulted in a 241-bp deletion, which decreased the number of amino acids and caused a frameshift translation. COLQ expression was significantly lower in the probands than in the probands' parents and siblings, while AChE expression was significantly higher. Moreover, the mutations were found to cause significant differences in the predicted three-dimensional structure of the protein. The splicing mutation c.393+1G>A, missense mutation c.1A>C (p.Q381P), and COLQ exon 14-15 deletion could cause CMS.

Congenital myasthenic syndrome with novel pathogenic variants in the COLQ gene associated with the presence of antibodies to acetylcholine receptors

Congenital myasthenic syndrome (CMS) is a heterogeneous group of inherited disorder which does not associate with anti-acetylcholine receptor (AChR) antibody. The presence of AChR autoantibody is pathogenic and highly sensitive and specific for autoimmune myasthenia gravis (MG). We describe 2 children from unrelated families who presented with hypotonia, ptosis and fatigability in early infancy with anti-AChR antibodies detected via ELISA on 2 separate occasions in the sera. Both were treated as refractory autoimmune MG due to poor clinical response to acetylcholinesterase inhibitor and immunotherapy. In view of the atypical clinical features, genetic studies of CMS were performed and both were confirmed to have novel pathogenic mutations in the COLQ gene. To the best of our knowledge, the presence of anti-AChR antibody in COLQ-related CMS has never been reported in the literature. The clinical presentation of early onset phenotype, and refractoriness to acetylcholinesterase inhibitor and immunotherapy should prompt CMS as a differential diagnosis.