When dementia affects children: Sanfilippo Syndrome
SanFilippo Syndrome is also known as mucopolysaccharidosis type 3A, and consists of an alteration in the functioning of certain cells called lysosomes: these are responsible for the breakdown and disposal of various substances
What is Sanfilippo Syndrome
In Sanfilippo Syndrome, this process does not occur for one sugar, called heparanesulphate, which then accumulates in lysosomes, causing the onset of dementia in children (Andrade et al., 2015).
However, there are some early onset symptoms, similar to those found in autism (hyperactivity, stereotypical behaviour, social behavioural changes) that cannot be explained by the accumulation of heparanesulphate.
Instead, it was seen that this would seem to result from an increased amount of dopamine in the brain, and the neurons that produce it; this phenomenon would not be caused by the accumulation of sugar, but by an altered functioning of it; it would therefore be a metabolic problem.
Furthermore, dopamine-producing neurons appear to be more numerous already in the foetus, which would allow Sanfilippo Syndrome to be considered a neurodevelopmental disorder.
The general prevalence is estimated at 1:70000 infants (Benetò et al., 2020), but could be skewed due to the difficulty in diagnosing the milder forms.
Furthermore, the different types have different prevalence depending on the geographical area: subtype A is more frequent in northern Europe, while subtype B is found more in the southern parts of the continent.
Subtype C is generally less common, while D is the rarest in all populations.
Diagnosis is made by analysing the amount of heparanesulphate in the urine.
Symptoms of Sanfilippo syndrome
The predominant aspect of the syndrome is a rapid mental deterioration. However, four different subtypes can be identified, depending on the genetic mutation involved and the resulting enzyme deficiency: type A, type B, type C and type D.
The symptomatology is however mainly shared by all subtypes: neurodegeneration begins in the first ten years of life, and includes cortical atrophy, progressive dementia, motor deterioration, hyperactivity, learning difficulties, aggressive behaviour, sleep disorders, and significant intellectual disability.
There may also be some somatic manifestations, including hirsutism, hepatosplenomegaly (enlarged liver and spleen), joint stiffness, dysphagia, hypertrichosis, hearing loss, speech loss, and skeletal changes; seizures usually occur after the age of 10.
Life expectancy for children affected by the syndrome is significantly lower than average, being between twenty and thirty years of age (Valstar et al. 2011).
There are currently no treatments that are effective in slowing or stopping neurodegeneration in children with Sanfilippo Syndrome
Intervention essentially consists of palliative measures to alleviate symptoms.
Several trials in animal and cellular models are currently underway, focusing mainly on intervention on the Central Nervous System.
These include enzyme replacement therapy (ERT), haematopoietic stem cell transplantation (HSCT), substrate reduction therapy (SRT), chaperone-mediated therapy and gene therapy.
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References:
Andrade, F.; Aldamiz-Echevarria, L.; Llarena, M.; Couce, M.L. (2015). Sanfilippo syndrome: Overall review. Pediatrics International, 57, 331–338.
Benetò, N., Vilageliu, L., Grinberg, D., Canals, I. (2020). Sanfilippo Syndrome: Molecular Basis, Disease Models and Therapeutic Approaches. International Journal of Molecular Sciences, 21(21), 7819.
Valstar, M.J.; Marchal, J.P.; Grootenhuis, M.; Colland, V.; Wijburg, F.A. (2011). Cognitive development in patients with Mucopolysaccharidosis type III (Sanfilippo syndrome). Orphanet Journal of Rare Diseases, 6, 43.
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