This study , published by the American College of Medical Genetics and Genomics, analyses clinical data for 87 patients with a molecularly confirmed diagnosis of MWS, including 62 previously reported patients and 25 unpublished cases, and compared them with patients previously reported by other authors. The data was obtained through collaborations involving clinicians from various countries. Such primary data have never been collated from a large cohort of affected individuals. In this article we present a comprehensive study of MWS features underlining a highly consistent phenotype for the disease, its genotype–phenotype correlations, and the phenotypic and clinical evolution taking place with age. The purpose of the article is to assist clinicians to identify the disease and to provide them with updated care recommendations for patient management.