Also known as Congenital Disorder of Glycosylation Type IIm
A rare, X-linked dominant, inherited condition caused by an abnormal enzyme disrupting glycosylation. Symptoms manifest in infancy, including seizures, hypotonia (low muscle tone), global developmental delay, failure to thrive, splenomegaly (enlarged spleen), hearing and vision loss, ataxia (impaired balance or coordination), hypertrophic cardiomyopathy, coarse facial features, short limbs, scoliosis, and thrombocytopenia (low blood platelet count).
SLC35A2-CDG is an inherited condition that affects many parts of the body. Individuals with SLC35A2-CDG typically develop signs and symptoms of the condition during infancy. Affected infants may have seizures (such as hypsarrhythmia), low muscle tone, global developmental delay, and a failure to gain weight and grow at the expected rate (failure to thrive). Their bodies can be formed differently with coarse facial features, recessed chin, multi-colored eyes, low-set ears, widely spaced and inverted nipples, and short limbs. Brain imaging may show a small cerebellum. Some patients have an enlarged spleen, scoliosis, hearing loss, and lack coordination. Affected individuals may have a heart condition, such as structural heart condition, fluid around the heart, or hypertrophic cardiomyopathy (insufficient pump function of the heart). Many have a visual impairment with structurally normal eyes. Those who are mildly affected may have isolated developmental delay and intellectual disability. Laboratory abnormalities may include elevated liver enzymes, abnormal coagulation factor activities, thrombocytopenia, and anemia. There are more than 60 SLC35A2-CDG patients published in the medical literature.
Diagnostic testing relies on testing the appropriate glycosylation of common proteins (one commonly used glycoprotein is transferrin). This can be tested by different methods in blood, but can also be normal in SLC35A2-CDG, particularly if the patient is no longer an infant. The ultimate diagnosis is genetic testing in blood. Individuals with SLC35A2-CDG have one faulty copy of the SLC35A2 gene, which is on the X chromosome. It is usually caused by a new genetic mutation in the affected individual and not inherited from a parent.
Treatment and Prognosis
There is a potential nutritional intervention treatment for SLC35A2-CDG, by oral D-galactose supplementation (D-galactose 1.5 g/kg/day, maximum dose 50 g/day). This treatment is still being tested on a research basis. All of the symptoms do not fully recover on this therapy, therefore the rest of the treatment focuses on identifying treatable medical conditions and preventing complications, (including supportive heart treatment, physical therapy, occupational therapy, etc.).