Mucopolysaccharidosis type I (MPS I) is a rare genetic condition, resulting from disease-causing changes in the IDUA gene called pathogenic variants. There are two different types of variants: • Null variants – cells cannot make the alpha-L-iduronidase enzyme • Missense variants – cells make a partly functional or severely reduced amount of the fully functional enzymeThe alpha-L-iduronidase enzyme breaks down large sugar molecules called glycosaminoglycans (GAGs). In people with MPS I, the enzyme is unable to break down GAGs and they build up in cells.Based on the severity of the condition, doctors categorise MPS I into two types, called phenotypes:• Attenuated MPS I • Severe MPS ITreatment options differ depending on MPS I phenotype. There are currently no tests that accurately determine MPS I phenotype. Using information from the MPS I Registry, researchers wanted to find out whether knowing the specific combination of the 2 disease-causing gene variants (genotype) can help predict whether a person has an attenuated or severe phenotypeThis Plain Language Summary of Publication article from Future Rare Disease discusses a rare genetic condition called mucopolysaccharidosis type I (MPS I). The summary describes a study where researchers wanted to find out whether knowing the specific combination of two disease-causing gene variants can help predict whether a person has an attenuated or severe phenotype.

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The original article on which this summary is based is called ‘Genotype-phenotype relationships in mucopolysaccharidosis type I (MPS I): Insights from the International MPS I Registry’ and is published in Clinical Genetics.

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