Acknowledgements
We thank the patients and their families for participating in this study. We thank the Center of Clinical Gene Diagnosis and Therapy of the State Key Laboratory of Medical Genetics of China for technical assistance.
Declaration of interest
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.
Funding
This study was supported by the National Natural Science Foundation of China (81370394) and the National Basic Research Program of China (973 Program) (2012CB517900).