COLQ-Congenital myasthenic syndrome in an Iranian cohort: the clinical and genetics spectrum

Abstract

Background: Congenital myasthenic syndrome (CMS) is a group of neuromuscular disorders caused by abnormal signal transmission at the motor endplate. Mutations in the collagen-like tail subunit gene (COLQ) of acetylcholinesterase are responsible for recessive forms of synaptic congenital myasthenic syndromes with end plate acetylcholinesterase deficiency. Clinical presentation includes ptosis, ophthalmoparesis, and progressive weakness with onset at birth or early infancy.

Methods: We followed 26 patients with COLQ-CMS over a mean period of 9 years (ranging from 3 to 213 months) and reported their clinical features, electrophysiologic findings, genetic characteristics, and therapeutic management.

Results: In our population, the onset of symptoms ranged from birth to 15 years. Delayed developmental motor milestones were detected in 13 patients (∼ 52%), and the most common presenting signs were ptosis, ophthalmoparesis, and limb weakness. Sluggish pupils were seen in 8 (∼ 30%) patients. All patients who underwent electrophysiologic study showed a significant decremental response (> 10%) following low-frequency repetitive nerve stimulation. Moreover, double compound muscle action potential was evident in 18 patients (∼ 75%). We detected 14 variants (eight novel variants), including six missense, three frameshift, three nonsense, one synonymous and one copy number variation (CNV), in the COLQ gene. There was no benefit from esterase inhibitor treatment, while treatment with ephedrine and salbutamol was objectively efficient in all cases.

Conclusion: Despite the rarity of the disease, our findings provide valuable information for understanding the clinical and electrophysiological features as well as the genetic characterization and response to the treatment of COLQ-CMS.

Keywords: COLQ gene; Acetylcholinesterase-associated collagen protein; Cholinesterase inhibitors; Congenital myasthenic syndrome (CMS); Muscle weakness.

Fig. 1

Geographical origin of 26 Iranian patients with COLQ-CMS

Fig. 2

(A) Mutations in the COLQ gene identified in our patients. The yellow boxes represent the exons but do not reflect the exon length. The novel mutations are marked in red. (B) Three COLQ domains [1]: conserved domains of COLQ include an N-terminal proline-rich attachment domain (PRAD) [2], a central collagen domain that contains two heparan sulfate proteoglycan binding (HSPBD) domains, and [3] a C-terminal region