Mucopolysaccharidosis (MPS) is subdivided into 6 types from type I to type VII. Mucopolysaccharidosis type I is known as Hurler syndrome, MPS III is known as Sanfilippo syndrome, MPS IV as Morquio syndrome, MPS VI as Maroteaux-Lamy syndrome and MPS VII as Sly syndrome. Hunter syndrome is type II mucopolysaccharidosis. They fall in the group of lysosomal storage diseases in which there is deficiency in inheriting an enzyme that is responsible in breaking down mucopolysaccharides, which are now known as glycosaminoglycans. Hunter syndrome is caused by deficiency or absence of iduronate 2-sulfatase deficiency (IDS). All of the above diseases have autosomal recessive inheritance pattern, except Hunter syndrome that has X-linked recessive pattern. Due to X-linked recessive pattern, Hunter syndrome is found exclusively in males because there is a rare chance of both X chromosomes affected in women.
What Are The Symptoms Of Hunter Syndrome?
Hunter syndrome is a chronic disease and can be further divided into two types, type A and type B. Type A mucopolysaccharidosis type II is the severe form and type B mucopolysaccharidosis type II is the milder form. The clinical course encompasses involvement of multiple organs along with their progressive deterioration. The phenotypic symptoms of the disease include enlargement of organs, coarse facial appearance, and growth failure. Hunter syndrome, in addition to other MPS and lysosomal storage disorders, has dysostosis complex, which is a combination of skeletal findings. These skeletal findings are large skull with J shaped sella, hypoplasia of pelvis with small femoral head and hip deformity, hypoplasia of thoracic and lumbar vertebrae, oar shaped ribs, tapering of proximal phalanges and diaphyseal and metaphyseal expansion of long bones. (1)
Type A Hunter syndrome usually presents itself in childhood at around the age of 2 to 4 years. The clinical features are a manifestation of continued neurological involvement. These include progressive coarsening of facial features, skeletal deformities, claw like appearance of fingers, broad chest, joint stiffness, kyphosis, stiff gait, short stature (seen after 3 years of age), short neck, delay in development, retinal degeneration, papilledema (due to optic nerve damage) leading to visual impairment, recurrent ear infections, progressive hearing loss (conductive, sensorineural or mixed), enlargement of tongue (greater in children >5 years), spacing between teeth, umbilical hernia, protuberance of abdomen, hepatosplenomegaly, carpal tunnel syndrome and severe disability in intellect.
Increased intracranial pressure can develop and neurological deterioration is more pronounced in the second and third decade of life and can even lead to seizures. The deposition of mucopolysaccharides in the heart can lead to can lead to valvular heart dysfunction, thickening of myocardium, coronary artery dysfunction, heart disease, pulmonary hypertension and respiratory disease. Gastrointestinal system may also be affected with the development of chronic diarrhea (younger people) and constipation (older people).
Hunter syndrome (both type A and type B) is characteristic of dermatological involvement. It shows skin lesions of ivory colored papules distributed symmetrically on upper back, upper arms and thighs. The skin lesions have reticular pattern and have pebble shaped appearance, which is the characteristic sign of the disease. In addition, there may also be thickening of skin, Mongolian spots found in the back and buttocks area, excessive hair growth that can even lead to unibrow.
Death is a result of cardiac compromise or airway obstruction or both.
Hunter type B is a milder form of type A and usually presents later in life when adolescent or adult. The rate of progression of the disease is usually slow and there is less disability in this type. Intellect of the patient is not affected. The physical symptoms of coarse facial features, hearing impairment, joint stiffness, airway obstruction, carpal tunnel syndrome and papilledema are still present. Skeletal deformities are mild with dysplasias of the pelvis, and femoral head without profound involvement of bony structures. Like in type A, type B patients also die of cardiac or respiratory complications; however, patients with Hunter type B can live beyond the fifth decade of life.