Contribution of intragenic deletions to mutation spectrum in Chinese patients with Wilson's disease and possible mechanism underlying ATP7B gross deletions.

Introduction: Wilson's disease (WD) is an autosomal recessive disorder of copper metabolism due to ATP7B pathogenic mutations. Disease manifestations can be prevented if early diagnosis and effective treatment are given. Direct sequencing is routinely used to confirm WD diagnosis, but cannot identify gross rearrangements.

Methods: Sanger sequencing of ATP7B was performed in 142 newly recruited WD index patients. The clinical effects of identified variants were classified according to American College of Medical Genetics and Genomics (ACMG) standards and guidelines. Multiplex ligation-dependent probe amplification (MLPA) was performed in 168 WD cases with clinical WD unexplained by Sanger sequencing, selected from our total case series of 774 WD patients. After identifying gross rearrangements within ATP7B, the breakpoints were determined by long-range PCR and direct sequencing.

Results: In the 142 WD patients, we identified 71 sequence alterations in ATP7B, of which 15 were novel; 14 of these were classified as 'pathogenic' or 'likely pathogenic', including 2 intronic variants affecting splice sites. In 6 of 168 WD patients, MLPA identified four heterozygous gross ATP7B deletions. One was a whole gene deletion, and three were intragenic deletions which were mapped to breakpoint locations, revealing non-homologous end joining.

Conclusion: Intragenic deletions are responsible for WD and non-homologous end joining could be the pathogenesis, therefore the detection of intragenic deletions should be included in comprehensive genetic testing for WD.