Case report: Dihydropyridine receptor (CACNA1S) congenital myopathy, a novel phenotype with early onset periodic paralysis

Abstract

Introduction: CACNA1S related congenital myopathy is an emerging recently described entity. In this report we describe 2 sisters with mutations in the CACNA1S gene and the novel phenotype of congenital myopathy and infantile onset episodic weakness.

Clinical description: Both sisters had neonatal onset hypotonia, muscle weakness, and delayed walking. Episodic weakness started in infancy and continued thereafter, provoked mostly by cold exposure. Muscle imaging revealed fat replacement of gluteus maximus muscles. Next generation sequencing found the missense p.Cys944Tyr variant and the novel splicing variant c.3526-2A>G in CACNA1S. Minigene assay revealed the splicing variant caused skipping of exon 28 from the transcript, potentially affecting protein folding and/or voltage dependent activation.

Conclusion: This novel phenotype supports the notion that there are age related differences in the clinical expression of CACNA1S gene mutations. This expands our understanding of mutations located in regions of the CACNA1S outside the highly conserved S4 segment, where most mutations thus far have been identified.

Keywords: CACNA1S; Cav1.1; DHPR; congenital myopathy; episodic weakness; novel phenotype; periodic paralysis; splice minigene assay.

Figure 1

MRI of the pelvis, thighs, upper limbs, and neck was performed on proband 1 using a 1.5T scanner (Toshiba, USA). Axial and coronal T1 and STIR sequences were obtained using a sense neuro vascular coil for the neck, and a multi coil for the rest. Axial T1 image at the level of the pelvic floor (A), and coronal T1 image of the thigh, (B) show symmetrical fat replacement of both gluteus maximus muscles (M), red and green arrows, respectively. The pelvic and thigh muscles bilaterally appear uninvolved. (C) Axial STIR images show suppression of the intramuscular fat (M).

Figure 2

(A) Pedigree. Sanger sequencing was used to study segregation in family members. Asymptomatic sister II.2 showed only c.3526-2A>G in heterozygosity while asymptomatic sister II.3 showed neither of the two variants. The arrow indicates Proband 1. (B) Bioinformatic analysis of novel variants.

Figure 3

Minigene assay. (A) Both c.3526-2A>G allele and WT allele from one of the patients were cloned in pcDNA3.1 plasmid and were transfected in tsA human epithelial kidney (HEK) cells. The genomic region cloned encompassed exons 26–30. (B) Agarose gel showing RT-PCR products derived from minigenes. The product from c.3526-2A>G allele is smaller than that of the WT allele. (C) Sequence electropherograms showing the effect of c.3526-2A>G in the alteration of physiological splicing of exon 28. Two independent transfections are shown. (D) Schematic representation of minigene products. Both transcripts lacked exon 29 which is alternatively spliced into embryonic tissues.