What is Mucopolysaccharidosis Type IIIB? Mucopolysaccharidosis type III, or Sanfilippo syndrome, consists of four disease sub-types based on the gene that causes the disease. All sub-types of MPS III are inherited lysosomal storage disorders and have similar clinical features. Mucopolysaccharidosis type IIIB (MPS IIIB), also known as Sanfilippo syndrome Type B, is caused by harmful changes (mutations) in the NAGLU gene. The symptoms associated with MPS IIIB are caused by a buildup of harmful substances in the central nervous system and cause progressive destruction of nerve cells. The severity of the disease can range from mild to severe, even among affected individuals in the same family. While infants with MPS IIIB appear normal at birth, delays in speech and motor skills may begin before one year of age, and nearly all children will experience some sort of developmental delay before six years of age. Children often have recurrent ear, nose, and throat infections. Behavioral issues, such as aggressiveness, sleeplessness, and hyperactivity, typically develop in early childhood, often between ages three and five years. Intellectual disability becomes more severe during this time period, in part because seizures frequently develop. Individuals may experience recurrent diarrhea and hearing loss. Many children start to lose the ability to speak by age 10. Motor problems, such as difficulty swallowing and stiff or rigid muscles (spasticity), will also develop. Most individuals with MPS IIIB lose the ability to walk by their mid-teens. Physical features of the disease can include coarse facial features, skeletal abnormalities, a large head (macrocephaly), and thick or excess body hair (hirsutism). Some affected individuals may develop heart problems as they get older. How common is Mucopolysaccharidosis Type IIIB? The incidence of MPS IIIB varies significantly by region. Where estimates have been made, the occurrence ranges from 1 in 125,000 to 1 in 500,000, with an average incidence of approximately 1 in 280,000. Incidence may be higher in individuals of southern European and Middle Eastern descent. How is Mucopolysaccharidosis Type IIIB treated? There is currently no cure for MPS IIIB. The treatment for MPS IIIB is based on the patient's particular symptoms and may include speech or occupational therapy for developmental delays, medication to treat seizures and recurrent infections, and ear tubes or hearing aids. Feeding tubes may be required in later stages of the disease. Overall, treatment is intended to relieve pain and increase the quality of life (palliative). What is the prognosis for an individual with Mucopolysaccharidosis Type IIIB? MPS IIIB is a progressive disease that has no cure, and affected individuals have a shortened lifespan. Most individuals with MPS IIIB do not survive past the second or third decade of life, with an average lifespan of approximately 15 years. However, there are rare reports of individuals with MPS IIIB who have lived into their fourth or fifth decade. Other names formucopolysaccharidosis type IIIB MPS3B N-acetyl-alpha-D-glucosaminidase deficiency NAGLU deficiency References Andrade et al., 2015, Pediatr Int, 57(3):331-8, PMID: 25851924 Héron et al., 2011, Am J Med Genet A, 155A(1):58-68, PMID: 21204211 Nijmeijer et al., 2019, J Inherit Metab Dis., 42(2):276-85, PMID: 30671988 Nijmeijer et al., 2019, Orphanet J Rare Dis. 14(1):249, PMID: 31718697 Valstar et al., 2008, J Inherit Metab Dis, 31(2):240-52, PMID: 18392742 Wagner et al., 2019, https://www.ncbi.nlm.nih.gov/books/NBK546574/