Mutations in both RyR1 and RyR2 are associated with a number of human diseases. Mutations in the RYR1 gene underlie several debilitating and/or life-threatening muscle diseases including malignant hyperthermia (MH) (
MacLennan et al. 1990), heat/exercise induced exertional rhabdomyolysis (
Capacchione et al. 2010), central core disease (CCD) (
Zhang et al. 1993), multiminicore disease (MmD) (
Ferreiro et al. 2002), and atypical periodic paralyses (APP) (
Zhou et al. 2010). Mutations in RyR2 cause/are associated with catecholaminergic polymorphic ventricular tachycardia (CPVT) and arrhythmogenic right ventricular dysplasia type 2 (ARVD2) (
Phillips et al. 1994,
Zhang et al. 1993,
Magee et al. 1956). Today around 300 mutations have been identified and linked to diseases associated with RyR ().
MH is an autosomal dominant disease in which genetically susceptible individuals respond to inhalation anesthetics (e.g., halothane) and muscle relaxants (e.g., succinylcholine) with sustained muscle contractions (
Mickelson and Louis 1996). More than 150 different point mutations in the RYR1 gene have been identified and linked to MH (). The majority of RyR1 mutations linked to MH cluster in the cytoplasmic domains of RyR1 (amino acids 35 to 614 and 2129 to 2458). Another cluster of mutations is found near the carboxyl terminus (4637 to 4973) (
Phillips et al. 1994;
Quane et al. 1994;
Lynch et al. 1999;
Monnier et al. 2000;
Scacheri et al. 2000;
Tilgen et al. 2001). MH is often a silent disorder that goes undetected until the patient undergoes surgery or is exposed to high ambient temperatures (~37°C) (
Jurkat-Roth et al. 2000). The underlying physiological consequence of MH is abnormal calcium homeostasis with increase sensitivity of channel opening in response to activators (
Tong et al. 1999).
An MH episode is characterized by elevations in body temperature, metabolic acidosis, hypoxia, tachycardia, skeletal muscle rigidity, and rhabdomyolysis (
Denborough et al. 1962;
Ellis et al. 1988;
Pamukcoglu 1988;
Britt et al. 1991;
Ryan and Tedeschi 1997) and is life threatening if not immediately treated with dantrolene, currently the only clinically approved treatment for MH (
Ward et al. 1986;
Zhao et al. 2001;
Paul-Pletzer et al. 2002). The incidence of MH is ~1 in 15,000 anesthetized children and ~1 in 50,000 to 100,000 anesthetized adults (
MacLennan 1992;
Strazis and Fox 1993;
Rosenberg et al. 2007). Another disorder related to MH is heat/exercise-induced exertional rhabdomyolysis; a clinical syndrome where heat/exercise-induced triggers breakdown of striated muscles that results in renal failure, hyperkalemia, and multi-organ failure. Approximately 26,000 cases are identified per year in United States (
Capacchione et al. 2010).
MmD is an autosomal recessive myopathy characterized by weakness in axial and proximal limb muscles, hypoxia, and muscle biopsies showing characteristic mini cores due to lack of oxidative enzyme activity (
Jungbluth 2007b;
Sharma et al. 2007).
APP are dominant and genetically heterogeneous conditions characterized by muscle weakness and are divided into hypokalemic periodic paralysis and hyperkalemic periodic paralysis. Mutations on SCN4A and CASNAS1S gene that codes for α1s subunit of DHPR have been identified as general cause of hypokalemic- and hyperkalemic-periodic paralysis, respectively. Recently in a patient suffering from MmD the RyR1 mutation Arg2939Lys has been identified and clinical features of the patient are reminiscent of hyperkalemic periodic paralysis, suggesting a new RyR1-related form of periodic paralysis with additional myopathy features (
Zhou et al. 2010).
Mutations in RyR2 produce altered Ca
2+ homeostasis leading to ARVD2 (
Dalla Volta et al. 1961;
Marcus et al. 1982;
Fontaine et al. 1984) and CPVT (
Marks et al. 2002;
Priori et al. 2002;
Laitinen et al. 2003). ARVD2 an autosomal dominant cardiac disease characterized by replacement of myocytes with fibro-fatty tissue leading to ventricular arrhythmias (
Corrado et al. 2000). Mutations in RyR2 are detected at three regions that are homologous to the mutations on RyR1 associated with MH and CCD. Studies in ARVD2 suggest that Ca
2+ leakage from myocardial SR via dysfunctional RyR2 is associated with development of ventricular arrhythmias (
Tiso et al. 2001). The incidence of ARVD2 is ~1 in 10,000 adults in United States (
Fontaine et al. 2001). CPVT is characterized by stress-induced ventricular tachycardia (
Marks et al. 2002;
Priori et al. 2002;
Laitinen et al. 2003). Roles for protein kinase A (PKA) and Ca
2+/calmodulin dependent protein kinase II (CaMKII) phosphorylation and enhancement of RyR2 open probability in these arrhythmias has been suggested (
Valdivia et al. 1995;
Marx et al. 2000;
Wehrens et al. 2004). In single channel recordings it has been shown that CPVT RyR2 mutation Arg4496Cys increases open probability at low Ca
2+ concentrations (~5 nM) but not at higher concentrations (~150 nM) (
Jiang et al. 2002;
Wehrens and Marks 2003). In patients with CPVT increased PKA phosphorylation and leaky RyR2 channels was observed during β-adrenergic stress and exercise. Binding studies in vitro suggested that the mutant RyR2 associated with CPVT have lower affinity for FKBP12.6 (
Wehrens et al. 2003). Later studies suggested that CPVT RyR2 expressing cells are more sensitive to β-adrenergic receptor stimulation (by either isoproterenol or forskolin) and have prolonged Ca
2+ transients under these conditions. This sensitivity does not appear to be caused by differences either in RyR2 phosphorylation or loss of FKBP12.6 (
George et al. 2003). Nonsense or missense mutations in the calsequestrin 2 gene have also been associated with autosomal recessive form of CPVT (
Lahat et al. 2001;
Postma et al. 2002).
RyR3 is the least studied ryanodine receptor, and consequently little is known of its function. Recently, RyR3 was suggested to play a role in Alzheimer’s disease, and up-regulation of RyR3 in cortical neurons is neuroprotective in TgCRND8 mouse model of Alzheimer’s disease (
Supnet et al. 2009).