Hypertrophic cardiomyopathy (HCM) is a well-recognized cardiac muscle disorder that has been known by various names, including idiopathic hypertrophic subaortic stenosis (IHSS). On echocardiography, the characteristic appearance includes a thickened ventricular septum and left ventricular posterior wall without an obvious etiology (eg, hypertension, aortic stenosis). The most common cause of HCM is now known to be one of over 200 possible mutations in at least 10 genes that involve sarcomeric proteins. 
Forms of HCM without evidence of mutations in sarcomeric proteins have also been identified. These diseases are a result of storage in cellular vacuoles and include Danon disease, Pompe disease, Fabry disease, and a form of HCM related to a mutation in the adenosine monophosphate (AMP)–activated, gamma-2 noncatalytic subunit of protein kinase (PRKG2).
In 1981, Danon described a multisystemic, lysosomal, glycogen-storage disease different from the previously described Pompe disease.  Danon disease is also known as lysosomal glycogen-storage disease with normal acid maltase. Danon disease is a rare form of HCM and muscular dystrophy. 
Various genetic causes result in HCM as an isolated finding. In Danon disease, however, although HCM is a major feature, other organ systems are also involved; the disease includes a component of skeletal myopathy with proximal-limb muscle weakness, mild muscular atrophy, elevated plasma concentrations of creatine kinase (CK), ophthalmologic involvement, possible mental retardation, and elevated hepatic enzyme levels. 
Lysosomal-associated membrane protein-2 (LAMP2) is a heavily glycosylated protein found inside the lysosomal membrane.  Microscopic characteristics of LAMP2 deficiency include small autophagic vacuoles in muscle fibers and excessive glycogen accumulation similar to that observed with maltase deficiency; however, acid maltase activity is normal.  The excessive intrasarcomeric glycogen is mostly responsible for the severe myocardial hypertrophy and is possibly responsible for pre-excitation.
A study by Hashem et al using induced pluripotent stem cell–derived cardiomyocytes indicated that LAMP2 protein deficiency in Danon disease results in autophagic flux impairment, which in turn causes excessive oxidative stress and, subsequently, cardiomyocyte apoptosis. 
In a study that included two girls, aged 10 and 13 years, Hedberg Oldfors et al found evidence that early onset HCM in Danon disease, in contrast to the late-onset cases that can occur, may result from an uneven distribution of LAMP2 protein in cardiac muscle, with the protein lacking in some large portions of the muscle, while its expression is preserved in other large myocardial areas. 
The incidence of Danon disease has not been determined. HCM is estimated to be present in 2 of every 1000 young adults, according to one large study. 
Charron et al examined 197 independent index cases with HCM.  Genomic sequencing for the LAMP2 gene revealed mutations in 2 of 197 (1%) patients with HCM.
In another study, 75 patients with possible HCM underwent genetic analysis, 6 had LAMP2 mutations. 
Reports from several countries describe Danon disease in patients of several nationalities. [10, 5] However, the incidence of Danon disease appears to be too low to allow investigators to estimate its frequency in a given population.
The prognosis for Danon disease in male patients is poor. Sugie et al reviewed the clinical features of 38 patients with genetically confirmed Danon disease.  The mean age at death was 19 years (± 6 y) in male patients compared with 40 years (± 7 y) in female patients. See Prognosis.
Reports of Danon disease have been published in several countries around the world.
Although HCM has been reported in different races and although several reports mentioned that multiple races were included in patient populations, no studies have described a racial distribution; some studies describe Danon disease only in whites. [8, 1, 11]
The disease is inherited as an X-linked dominant trait, although spontaneous mutations have been reported in several families. 
Males are usually more severely affected than females, particularly in degree of cardiomyopathy and age of death. This difference is at least partially explained by a gene-dosage effect.  Male individuals have only one X chromosome with the LAMP2 mutation, and most female individuals have one X chromosome with the mutation and one normal X chromosome; therefore, the effect is most pronounced in males. Maron et al reported 7 patients with LAMP2 mutations who have severe HCM, including one a female diagnosed at age 11 years with maximal LV thickness of 30 mm. 
The age of presentation is somewhat variable. The greatest factor that affects the age at presentation is the patient's sex. The age at presentation can range from infancy to the second decade in males but is less well defined in females. Male patients typically present in their teens and rarely survive beyond their 20s. [2, 12, 4, 11]
Lacoste-Collin et al reported a new diagnosis of Danon disease in a 41-year-old man. 
Van der Kooi et al reported several males from the same family with the proband who presented at age 46 years.  Other male siblings had symptoms beginning in the mid 40s and are still alive in their 60s. Interestingly, a female sibling died suddenly at age 13 years.
In a series by Sugie et al, the age at presentation in males ranged from 10 months to 19 years (17 ± 7 y), with a mean age of death at 19 years (± 6 y).  Female patients have a relatively mild form of the disease and often survive into their 30s and 40s. For female patients, the mean age at presentation was 38 years (± 12 y) with a mean age at death of 40 years (± 7 y).
What would you like to print?