Singleton Merten syndrome

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Singleton Merten syndrome
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Overview

Singleton-Merten syndrome is an extremely rare, inherited, multisystem disorder in which the major characteristics are abnormalities of tooth (dental dysplasia), calcifications in the aorta (the biggest artery of the body), and certain valves of the heart (aortic and mitral valves), and progressive thinning and weakness of the bones (osteoporosis), typically in the hands and feet.

Females have been affected more frequently than males in a ratio of 3 to 1. Less than 10 individual cases have been reported in the medical literature along with three families with multiple affected members.

Causes:

Singleton-Merten syndrome, an inherired disorder, is caused due to a mutation in the IFIH1 gene, the gene responsible for making 'melanoma differentiation-associated gene 5' (MDA5) protein.

MDA5 protein, normally activated in the presence of virus, in individuals with Singleton-Merten syndrome, appears to always be activated, even in the absence of any virus infection, leading to an overactive immune system. This immune state may derange calcium metabolism in the body, leading to abnormal calcification of the cardiac valves and aorta, and loss of calcification in the bones.

Another gene, DDX58, has been associated with atypical Singleton-Merten syndrome.

Signs and symptoms:

Common physical findings and symptoms associated with Singleton-Merten syndrome include generalized weakness of muscles, progressive loss or wasting away of muscle tissue (muscle atrophy), delayed physical growth, possibly resulting in delayed development and short stature, thickened patches of red, scaly skin, particularly on the fingers, vision problems, eye redness, blurred vision, delay in ability to coordinate muscles and carry out certain tasks, and malformation of the hips and feet.

Affected patients may develop dental cavities (caries) and suffer with premature loss of their primary (deciduous) teeth. Certain permanent teeth may not develop at all, or may erupt late, and when erupted, are usually malformed (dysplastic).

Secondary to the calcification of aorta and cardiac valves, affected individuals may experience hypertension, abnormal electrical impulses that coordinate the activity of the heart muscle (heart block), abnormal heart contractions (systolic murmurs), and enlargement of the heart (cardiomegaly). As the patients grow older, usually by late adolescence, the heart may not be to pump blood effectively, leading to heart failure, a potentially life-threatening situation.

Other observable signs and symptoms include abnormal thinning and weakness of the bones, muscle weakness and malformations of the hips and feet, and abnormal sensitivity to light. Typical facial features of Singleton Merten syndrome include high anterior hairline, drooping of the upper eyelids (ptosis), broad forehead, loss of vertical groove between the nose and upper lip (philtrum), and a thin upper lip border (vermillion).

Mild form of Singleton-Merten syndrome may be associated wth only one symptom, such as a skin rash (psoriasis).

Diagnosis:

Diagnosis of singleton-merten syndrome may be confirmed by a thorough clinical evaluation based upon the identification of characteristic physical findings, a detailed patient history, and specialized tests.

X-ray tests are carried out to confirm the presence and extent of calcium deposits in the aorta. Cardiac catheterization is done to confirm narrowing of the affected heart valves. X-ray of bones of hands and feet might reveal abnormal widening of the bone marrow cavities.

Management:

Treatment requires the coordinated efforts of a team of specialists, including pediatricians, surgeons, cardiologists, dentists, physical therapists, dermatologists, and other health care professionals that work together to comprehensively plan a patient's treatment.

Specific therapies are symptomatic and supportive in nature. Affected children must be provided with physical therapy, medical, social, and vocational services. Genetic and psychosocial counselling of the affected families must be undertaken.

Other names for this condition:

Merten-Singleton syndrome