MED13L haploinsufficiency syndrome: A de novo frameshift and recurrent intragenic deletions due to parental mosaicism

MED13L haploinsufficiency syndrome is a clinical condition manifesting intellectual disability and developmental delay in association with various complications including congenital heart defects and dysmorphic features. Most of the previously reported patients showed de novo loss-of-function mutations in MED13L. Additional three patients with MED13L haploinsufficiency syndrome were identified here in association with rare complications. One patient had a de novo deletion (c.257delT) and T2-weighted high intensity in the occipital white matter on magnetic resonance imaging. Two siblings exhibited an intragenic deletion involving exons 3-14, which led to an in-frame deletion in MED13L. The deletion was inherited from their carrier mother who possessed low frequency mosaicism. The older sister of the siblings showed craniosynostosis; this condition has never been reported in patients with MED13L haploinsufficiency syndrome. Dysmorphic features were observed in these patients; however, most of the findings were nonspecific. Further information would be necessary to understand this clinical condition better.