A rare case of unilateral adrenal hyperplasia accompanied by hypokalaemic periodic paralysis caused by a novel dominant mutation in CACNA1S: features and prognosis after adrenalectomy

Towards Zebrafish Models of CNS Channelopathies

Channelopathies are a large group of systemic disorders whose pathogenesis is associated with dysfunctional ion channels. Aberrant transmembrane transport of K⁺, Na⁺, Ca²⁺ and Cl^- by these channels in the brain induces central nervous system (CNS) channelopathies, most commonly including epilepsy, but also migraine, as well as various movement and psychiatric disorders. Animal models are a useful tool for studying pathogenesis of a wide range of brain disorders, including channelopathies. Complementing multiple well-established rodent models, the zebrafish (Danio rerio) has become a popular translational model organism for neurobiology, psychopharmacology and toxicology research, and for probing mechanisms underlying CNS pathogenesis. Here, we discuss current prospects and challenges of developing genetic, pharmacological and other experimental models of major CNS channelopathies based on zebrafish.

Mutations associated with hypokalemic periodic paralysis: from hotspot regions to complete analysis of CACNA1S and SCN4A genes

Familial periodic paralyses (PPs) are inherited disorders of skeletal muscle characterized by recurrent episodes of flaccid muscle weakness. PPs are classified as hypokalemic (HypoPP), normokalemic (NormoPP), or hyperkalemic (HyperPP) according to the potassium level during the paralytic attacks. HypoPP is an autosomal dominant disease caused by mutations in the CACNA1S gene, encoding for Cav1.1 channel (HypoPP-1), or SCN4A gene, encoding for Nav1.4 channel (HypoPP-2). In the present study, we included 60 patients with a clinical diagnosis of HypoPP. Fifty-one (85%) patients were tested using the direct sequencing (Sanger method) of all reported HypoPP mutations in CACNA1S and SCN4A genes; the remaining 9 (15%) patients were analyzed through a next-generation sequencing (NGS) panel, including the whole CACNA1S and SCN4A genes, plus other genes rarely associated to PPs. Fifty patients resulted mutated: 38 (76%) cases showed p.R528H and p.R1239G/H CACNA1S mutations and 12 (24%) displayed p.R669H, p.R672C/H, p.R1132G/Q, and p.R1135H SCN4A mutations. Forty-one mutated cases were identified among the 51 patients managed with Sanger sequencing, while all the 9 cases directly analyzed with the NGS panel showed mutations in the hotspot regions of SCN4A and CACNA1S. Ten out of the 51 patients unresolved through the Sanger sequencing were further analyzed with the NGS panel, without the detection of any mutation. Hence, our data suggest that in HypoPP patients, the extension of genetic analysis from the hotspot regions using the Sanger method to the NGS sequencing of the entire CACNA1S and SCN4A genes does not lead to the identification of new pathological mutations.

Inherited Neuromuscular Disorders: Which Role for Serum Biomarkers?

Inherited neuromuscular disorders (INMD) are a heterogeneous group of rare diseases that involve muscles, motor neurons, peripheral nerves or the neuromuscular junction. Several different lab abnormalities have been linked to INMD: sometimes they are typical of the disorder, but they usually appear to be less specific. Sometimes serum biomarkers can point out abnormalities in presymtomatic or otherwise asymptomatic patients (e.g., carriers). More often a biomarker of INMD is evaluated by multiple clinicians other than expert in NMD before the diagnosis, because of the multisystemic involvement in INMD. The authors performed a literature search on biomarkers in inherited neuromuscular disorders to provide a practical approach to the diagnosis and the correct management of INMD. A considerable number of biomarkers have been reported that support the diagnosis of INMD, but the role of an expert clinician is crucial. Hence, the complete knowledge of such abnormalities can accelerate the diagnostic workup supporting the referral to specialists in neuromuscular disorders.

CACNA1S Arg528Cys mutation in a young Chinese man with thyrotoxic hypokalemic periodic paralysis

It has long been believed that the patients with thyrotoxic hypokalemic periodic paralysis (THPP) may harbor genetic mutations commonly found in familial hypokalemic periodic paralysis. Despite extensive testing, such a mutation has escaped detection until now.

Impact of immunohistochemistry on the diagnosis and management of primary aldosteronism: An important tool for improved patient follow-up

BACKGROUND AND AIMS

Primary aldosteronism is a common cause of secondary hypertension. Primary aldosteronism is caused by an aldosterone-producing adenoma or bilateral hyperplasia that in some cases is asymmetrical with one adrenal dominating aldosterone secretion. Most patients with aldosterone-producing adenoma are biochemically cured by unilateral adrenalectomy, but patients with bilateral hyperplasia have a significant risk of residual or recurrent disease. Here, immunohistochemistry of CYP11B1 and B2 was used to investigate whether these markers could aid in the diagnostic workup of primary aldosteronism patients.

MATERIALS AND METHODS

A total of 39 patients with primary aldosteronism who underwent unilateral adrenalectomy for a presumed adenoma during 2013-2016 were included. Immunohistochemistry using monoclonal antibodies identifying the enzymes CYP11B1 and B2 was part of routine histopathological workup in 6 cases; in 33 cases, it was applied retrospectively. The hyperplasia diagnosis was suggested when there was no dominating nodule but immunoreactivity for CYP11B2 was seen in several nodules, which were also seen on routine sections. To distinguish between adenoma and hyperplasia, a ratio between the largest and second largest CYP11B2-positive nodules was calculated.

RESULTS

In all, 22 patients had an aldosterone-producing adenoma, while 13 patients were judged to have hyperplasia. In four cases, a final diagnosis could not be established, thus these were judged equivocal. Among the 33 cases investigated retrospectively, the primary histopathological diagnosis was altered from hyperplasia to aldosterone-producing adenoma in 9 cases (27%) after immunohistochemistry, and the immunohistochemically rectified adenoma group displayed improved clinical cure rates compared to the routine H&E-diagnosed cohort. Moreover, the B2 ratio was significantly higher in adenoma than in hyperplasia and equivocal cases.

CONCLUSION

Immunohistochemistry detecting CYP11B1 and B2 expression is of great help in establishing a final histopathological diagnosis in patients with primary aldosteronism. This procedure should be part of the histopathological routine in all operated primary aldosteronism patients.

Rhabdomyolysis and fluctuating asymptomatic hyperCKemia associated with CACNA1S variant

BACKGROUND AND PURPOSE

CACNA1S encodes Ca_v 1.1, a voltage sensor for muscle excitation-contraction coupling, which activates the ryanodine receptor 1 (RYR1) leading to calcium release from the sarcoplasmic reticulum. CACNA1S mutations cause hypokalemic periodic paralysis, malignant hyperthermia and congenital myopathy. RYR1 mutations result in congenital myopathy, malignant hyperthermia and rhabdomyolysis.

METHODS

The aim was to describe a novel phenotype associated with a CACNA1S variant at a site previously linked to hypokalemic periodic paralysis.

RESULTS

The patient presented with fluctuating asymptomatic creatine kinase elevation after an episode of rhabdomyolysis but has no history of periodic paralysis. His muscle biopsy showed core-like structures occurring mainly in type 2 fibers. He carries a novel Ca_v 1.1 variant (p.Arg528Leu) affecting a highly conserved amino acid. Different mutations at the same location cause hypokalemic periodic paralysis.

CONCLUSION

This case underscores the similarity between the phenotypes caused by mutations in two functionally linked proteins, RYR1 and Ca_v 1.1.