Evaluation and follow-up of newborns screening positive for mucopolysaccharidosis II: Results from an international modified Delphi consensus.

Mucopolysaccharidosis II (MPS II; Hunter syndrome; OMIM 309900) is a rare, X-linked lysosomal storage disease caused by deficient activity of the enzyme iduronate-2-sulfatase (I2S, EC 3.1.6.13), due to pathological variants of the I2S gene (IDS). Clinically, MPS II is a chronic progressive multisystem developmental and degenerative disorder, typically associated with manifestations in early childhood. Intravenous enzyme replacement therapy has been available since 2006, with improved outcomes seen with early initiation of therapy. Newborn screening for MPS II in a public health setting has been ongoing in Taiwan since 2015 and in some states of the USA since 2017. These developments prompted a successful nomination of MPS II to be included as a core screening condition on the US Federal Recommended Uniform Screening Panel (RUSP), which was approved by the US Secretary of Health and Human Services on August 2, 2022. With the promise of expanded public health screening for MPS II, there was a perceived need for a set of consensus recommendations on MPS II newborn screening, the clinical confirmation of screened positive cases, and their clinical management. To this end an international expert panel of 21 members from 8 countries was convened to conduct a modified Delphi consensus on the evaluation and follow-up of newborns who screened positive for MPS II, the results of which are presented.