Diagnosis; Mutation Confirmation; Predictive; Prognostic

Mutations in the SCN4A gene have been identified in a group of related muscular disorders, including hyperkalemic periodic paralysis (HYPP; 170500), paramyotonia congenita (PMC; 168300), a group of disorders classified as potassium-aggravated myotonia (608390), and hypokalemic periodic paralysis type 2 (HOKPP2; 613345).

Establish or confirm diagnosis

(hyperPP1) is characterized by attacks of flaccid limb weakness (which may also include weakness of the muscles of the eyes, throat, and trunk), hyperkalemia (serum potassium concentration >5 mmol/L) or an increase of serum potassium concentration of at least 1.5 mmol/L during an attack of weakness and/or provoking/worsening of an … (hyperPP1) is characterized by attacks of flaccid limb weakness (which may also include weakness of the muscles of the eyes, throat, and trunk), hyperkalemia (serum potassium concentration >5 mmol/L) or an increase of serum potassium concentration of at least 1.5 mmol/L during an attack of weakness and/or provoking/worsening of an attack by oral potassium intake, normal serum potassium and muscle strength between attacks, onset before age 20 years, and absence of paramyotonia (muscle stiffness aggravated by cold and exercise) View more

All coding exons and 20 bp of flanking intronic sequence are enriched using an LHSC custom targeted hybridization protocol (Roche Nimblegen), followed by high throughput sequencing (Illumina). This chemistry and analysis pipeline provides a highly sensitive and specific detection of sequence and copy number alterations in a single assay that … All coding exons and 20 bp of flanking intronic sequence are enriched using an LHSC custom targeted hybridization protocol (Roche Nimblegen), followed by high throughput sequencing (Illumina). This chemistry and analysis pipeline provides a highly sensitive and specific detection of sequence and copy number alterations in a single assay that exceeds the previous gold standard of Sanger sequence and MLPA. Sequence variants and copy number changes are assessed and interpreted using clinically validated algorithms and commercial software (SoftGenetics: Nextgene, Geneticist Assistant, Mutation Surveyor; and Alamut Visual). All genes have >1000x mean read depth coverage, with a minimum 200x coverage at a single nucleotide resolution. Mitochondrial DNA testing is validated for heteroplasmy detection sensitivity of 2-5%. All variants interpreted as either ACMG category 1, 2, or 3 (pathogenic, likely pathogenic, VUS; PMID: 25741868) are confirmed using Sanger sequencing, MLPA, or other assays. ACMG category 4 and 5 variants (likely benign, benign) are not reported, but are available upon request. View more

Mutations identified are repeated in an independent assay using either Sanger sequence or MLPA

Tests performed
Entire test performed in-house

This assay meets the sensitivity and specificity of combined Sanger sequencing and MLPA copy number analysis, >99%

Is proficiency testing performed for this test? Help
No

Software used to interpret novel variations Help
SoftGenetics: Nextgene, Geneticist Assistant, Mutation Surveyor; and Alamut Visual

Laboratory's policy on reporting novel variations Help
All variants interpreted as either ACMG category 1, 2, or 3 (pathogenic, likely pathogenic, VUS; PMID: 25741868) are confirmed using Sanger sequencing, MLPA, or other assays. ACMG category 4 and 5 variants (likely benign, benign) are not reported, but are available upon request.