Phenotypic Diversity of 15q11.2 BP1-BP2 Deletion in Three Korean Families with Development Delay and/or Intellectual Disability: A Case Series and Literature Review.

The 15q11.2 breakpoint (BP) 1-BP2 deletion syndrome is emerging as the most frequent pathogenic copy number variation in humans related to neurodevelopmental diseases, with changes in cognition, behavior, and brain morphology. Previous publications have reported that patients with 15q11.2 BP1-BP2 deletion showed intellectual disability (ID), speech impairment, developmental delay (DD), and/or behavioral problems. We describe three new cases, aged 3 or 6 years old and belonging to three unrelated Korean families, with a 350-kb 15q11.2 BP1-BP2 deletion of four highly conserved genes, namely, the TUBGCP5, CYFIP1, NIPA2, and NIPA1 genes. All of our cases presented with global DD and/or ID, and the severity ranged from mild to severe, but common facial dysmorphism and congenital malformations in previous reports were not characteristic. The 15q11.2 BP1-BP2 deletion was inherited from an unaffected parent in all cases. Our three cases, together with previous findings from the literature review, confirm some of the features earlier reported to be associated with 15q11.2 BP1-BP2 deletion and help to further delineate the phenotype associated with 15q11.2 deletion. Identification of more cases with 15q11.2 BP1-BP2 deletion will allow us to obtain a better understanding of the clinical phenotypes. Further explanation of the functions of the genes within the 15q11.2 BP1-BP2 region is required to resolve the pathogenic effects on neurodevelopment.