Long‐Read Sequencing Expands the Genotypic Spectrum of Patients With Mucopolysaccharidosis Type <scp>II</scp>

The substantial genetic heterogeneity associated with mucopolysaccharidosis type II (MPS II) poses major challenges to current genetic testing. A comprehensive analysis of MPS II (CAMPS II), integrating long-range PCR with long-read sequencing (LRS), was established to identify IDS variants in 92 patients with clinically suspected MPS II. Comparative analysis against conventional genetic testing including multiplex ligation-dependent probe amplification (MLPA) and Sanger sequencing revealed concordant results in 75% (69/92) of cases, with discordant results in 25% (23/92) of cases. Among 23 discordant cases, CAMPS II newly identified IDS variants in 18 patients and enhanced variant detection in five patients. The diagnostic yield of CAMPS II for pathogenic variants was 82.6% (76/92), significantly higher than 66.3% (61/92) with conventional methods. CAMPS II expanded the genotypic spectrum in 92 probands, including 79.3% (73/92) SNVs/Indels, 15.2% (14/92) IDS/IDSP1 inversions, 2.2% (2/92) complete IDS deletions, 2.2% (2/92) gross deletions/duplications, and 1.1% (1/92) IDS/IDSP1 deletions. Moreover, 14.1% (13/92) of the patients carried novel variants. Junction characterization in 15 patients with complex rearrangement revealed hotspot regions prone to inversion and conversion events. Above all, this study highlights the advantages of CAMPS II in identifying diverse IDS variants, improving diagnostic yields, and identifying carrier status.