Mucopolysaccharidosis (MPS) is a group of lysosomal storage diseases caused by an inherited deficiency of an enzyme involved in the breaking down of glycosaminoglycans (mucopolysaccharides). First MPS was described in 1919 by Dr. Gertrud Hurler and later named Hurler’s syndrome. From 1929 to 1962 scientists discovered and described all forms of MPS known today (Muenzer, 2011).
Currently there are seven main forms of MPS and numerous subtypes. Different types of mucopolysaccharidosis have their own characteristics. But traditionally MPS is divided into two main phenotypes: the Hurler-like phenotype and the Morkquio-like phenotype. The Hurler-like phenotype is often accompanied by dementia, hepatosplenomegaly and peculiar apperance and facial features (elongated appearance of the head, low nasal bridge, prominent foreheads, flattened appearance of the face, short and stiff neck, and abnormal curvature of the lower spine). The Morkquio-like phenotype represents the attenuated form of MPS when patients do not have coarse facial features or mental retardation. Other common symptoms of MPS are disproportionately short trunk (dwarfism), visual impairment (corneal opacity, etc.), hearing impairment (hearing loss), heart and vascular diseases (arrhythmias, myocardial hypertrophy, and heart valve diseases), respiratory system diseases (Bukhari, 2015).
MPS II is X-linked disorder that is caused by a deficiency of iduronate 2-sulfatase (IDS) and missense mutations, whereas all other forms of MPS are autosomal recessive disorders. As of today, at least 530 genetic mutations responsible for MPS II are identified, besides it is confirmed that gross alterations lead to severe form. Missense mutations comprising around one third of the MPS II mutations lead to heterogeneous phenotypes that range from severe to attenuated form (Hopwood, Bunge, Morris, et al., 1993).
Urine test to look for abnormally high levels of glycosaminoglycans (GAGs) is the initial step in diagnosis of MPS. However, more definitive diagnosis requires a test measuring enzyme activity levels in the blood or skin cells. Finally, DNA testing allows to detect the specific genetic changes that code for the missing enzyme. Since MPS I is an inherited disorder, family screening is crucial. Prenatal and newborn screenings are also available (Lehman, Miller, Norquist, et al., 2011).
Prognosis depends on the form and severity of MPS.