Description, Causes and Risk Factors:
Naxos disease is an autosomal recessive disorder that combines palmoplantar keratoderma and othre ectodermal features with cardiac disorders suggesting arrhythomogenic right ventricular dysplasia/cardiomyopathy. It was first reported in families on the Greek island of Naxos by Protonotarios. The association of curly hair and the cardiac abnormality with palmoplantar keratoderma is reported in literature.
Naxos disease is characterized by wolly hair, diffuse palmoplanter keratoderma with clear borders and sometimes erythematous appearing within the first year of life. Cardiac abnormalities will not appear until late puberty which include ventricular arrhythmias, heart failure, dilated cardiomyopathy or even sudden death.
The disease was first described by Protonotarios in families originating from the Greek island of Naxos. Apart from Naxos, affected families have been detected in other Greek Aegean islands, Turkey, Israel and Saudi Arabia. The prevalence of the disease in the Greek islands may be as high as 1:1000. A variety of Naxos disease, reported as Carvajal syndrome, has been described in families from India and Ecuador. It clinically presents at younger age with predominantly left ventricular involvement leading to early heart failure and exhibits a clinical phenotype similar to that of dilated cardiomyopathy.
Genetic studies have located two causative genes, encoding for the proteins plakoglobin and desmoplakin. Plakoglobin and desmoplakin are proteins of cell-cell adhesion. A 2-base-pair deletion mutation of the plakoglobin gene (Pk2157del2TG) truncating the C-terminal of the protein causes Naxos disease. This mutation was identified in 13 families from Greece and in one family from Turkey. The prevalence of heterozygous carriers is up to 5% of the Naxos population (20,000 inhabitants). Heterozygotes present normal phenotype except in a small minority who show woolly hair as well as a few electrocardiographic or echocardiographic abnormalities not fulfilling the criteria for ARVC. Two different mutations of the desmoplakin gene (Dsp7901del1G and DspG2375R), truncating the C-terminal of the protein, have been found to underlie a similar cardiocutaneous syndrome in families from Ecuador and Israel.
Researchers speculate that in Naxos disease the disruption of desmosomes function (caused by the mutant plakoglobin under mechanical stretch) leads to detachment of the myocytes at the intercalated disc with progressive myocyte death. Apoptotic myocardial cell death has been reported to occur in ARVC; also it seems that plakoglobin is involved in the pathways of apoptosis. The reason for preferential involvement of the right ventricle could be related to the early exposure of the right ventricular myocardium to mechanical stretch especially during the fetal period. An increased mechanical stretch of the heart might have a triggering effect for a rapid and massive myocardial cell detachment and apoptotic cell death. This could explain the severity of the disease in the young.
The symptoms of Naxos disease are more critical and severe compared to autosomal dominant arrhythmogenic right ventricular dysplasia (ARVD). The following are some of the symptoms of this disorder:
Thickened skin on soles.
Thickened skin on palms.
In order to make the diagnosis of Naxos disease being a variant of ARVD includes the following:
Electrocardiogram (EKG or ECG), which has the ability to record the electrical activity of the heart overtime.
Echocardiography is also called as the ultrasound of the heart.
Right ventricular angiography, which is considered to be the gold standard in the diagnosis of all ARVD.
The primary goal is the prevention of sudden cardiac death. Implantation of an automatic cardioverter defibrillator (ICD) is indicated in patients who develop symptoms and/or structural progression, particularly before the age of 35 years. Antiarrhythmic drugs are indicated for preventing recurrences of episodes of sustained ventricular tachycardia; sotalol and amiodarone, either alone or in combination with classical ?-blockers, seem to be the most effective. Patients with congestive heart failure are managed with diuretics and angiotensin-converting enzyme (ACE) inhibitors, while heart transplantation is considered at the end stages.
In an attempt to control Naxos disease, systematic genetic screening of the populations at risk has been initiated and is starting to identify the heterozygous carriers of the plakoglobin gene mutation.
NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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