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Synonym: mucopolysaccharidosis type IH, mucopolysaccharidosis I, MPS I
The mucopolysaccharidoses are a group of inherited disorders caused by a lack of specific lysosomal enzymes involved in the degradation of glycosaminoglycans (GAGs). Deficiency of alpha-L-iduronidase can result in a wide range of phenotypes including Hurler's (severe), Scheie's (mild) and Hurler-Scheie (intermediate) syndromes. The genetic defect involves a mutation in the gene IDUA that encodes alpha-L-iduronidase on chromosome 4.
- One study, using a unique longitudinal data set, initiated and maintained over a period of more than 20 years by the Society for Mucopolysaccharide Diseases (UK), found a birth prevalence in England and Wales of 1.07/100,000.
- The mode of inheritance is autosomal recessive.
Affected children appear normal at birth but usually develop the characteristic appearance within the first year of life. The median age of onset of symptoms is 6 months.
- General learning disability: maximum functional development is reached when the child is aged between 2 and 4 years.
- Short stature.
- Coarse facies and enlarged tongue.
- Corneal clouding.
- Hearing impairment.
- Umbilical and inguinal hernias.
- Joint stiffness and skeletal deformities.
- Cardiomyopathy and coronary heart disease.
- Dysostosis multiplex: enlarged skull, enlarged but shortened bones, malformed pelvis, and other skeletal defects.
- Other mucopolysaccharidoses: Hunter's syndrome (mucopolysaccharidosis type II) has no corneal clouding and progression is slower.
- Other causes of general learning disability and short stature.
- Urine: raised levels of dermatan sulfate and heparan sulfate (metabolites related to GAG) are found in patients with mucopolysaccharidoses.
- Lymphocytes examined in blood smears may show abnormal cytoplasmic inclusions.
- Definitive diagnosis is established by alpha-L-iduronidase enzyme assay using artificial substrates in cultured fibroblasts or isolated leukocytes.
- Carrier testing can be performed by differentiating normal enzyme activity from half-normal levels of enzyme activity.
- Prenatal diagnosis: using cultured amniotic fluid cells or chorionic villus biopsies.
- Molecular diagnosis: difficult because of genetic heterogeneity.
- Assessment of complications will include an echocardiogram and MRI brain scan.
- In severe cases, radiography of the skeleton (especially the spine) may detect a gibbus deformity of the lower spine.
- A mild form of dysostosis multiplex may be seen on X-ray.
- Ultrasound imaging of the ophthalmic nerve sheath and sclera is a useful technique for assessing the presence of morphological changes.
- Palliative treatment includes the provision of multidisciplinary treatment and support for affected children and their families.
- Orthopaedic surgery for joint contractures and skeletal deformities.
- Other surgical procedures may include myringotomy, hernia repair and adenoidectomy/tonsillectomy.
- Corneal transplants may be required.
- Enzyme replacement therapy with laronidase can be used pre- and peri-haemopoietic stem cell transplant, which is now the gold standard treatment in those patients diagnosed under 2.5 years of age.[7, 8, 9]
- Gene therapy may present treatment possibilities in the future.
- Orthopaedic complications lead to pain and immobility.
- Upper airways obstruction; progressive airway, craniofacial and skeletal abnormalities may make both ventilation and intubation difficult.
- Increased susceptibility to infections of the respiratory tract.
- There is a high morbidity and mortality, causing in many cases severe neurological and somatic damage in the first years of life.
- The median survival for mucopolysaccharidosis I (MPS I) patients is 11.6 years.
- Common causes of death include upper airways obstruction, cardiac insufficiency and respiratory tract infections.
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