The disease itself
Sanfilippo syndrome is caused by the accumulation of partially degraded heparan sulfate molecules in body’s tissues (heparan sulfate is a polysaccharide found in all animal tissues). This occurs as a consequence of a genetic mutation affecting the activity of an enzyme necessary for heparan sulfate degradation. Undigested molecules, which cannot be eliminated, impair normal brain development and further kill brain cells.
The first symptoms of the disease – delayed cognitive development associated with hyperactivity, autistic behavior and sleep disorders – usually appear before the ages of 3 years. Neurological damage subsequently causes intellectual deficiencies and reduced motor skills, leading to a loss of autonomy at about 10 years of age. There is also slight facial dysmorphia.
Epidemiology
Sanfilippo syndrome is often diagnosed late. Incidence in France, UK and Greece has been documented in a retrospective epidemiological study conducted by the Institut Pasteur and the AP-HP in 2009 (Héron B et al. Incidence and natural history of mucopolysaccharidosis type III in France and comparison with United Kingdom and Greece. Am J Med Genet A. January, 2011). It varies from 0.6 to 1.2 diagnosed cases per 100,000 life births.
There are four types of Sanfilippo syndrome – A, B, C and D – and each type is caused by a different enzyme deficiency. Genetic transmission, the same for the four types, is recessive autosomic: a child has a risk of being affected if both parents carry a genetic mutation associated with the disease. The clinical expression of the two most common types – type A and type B – is identical.
Treatment and management
There is currently no treatment for the disease, while care of the symptoms is difficult. Supplying functional enzyme, especially to the brain very early in life is presumably the best strategy to modify the dramatic natural course of the disease.
June 2021
