ObjectivesNeurodevelopmental disorders (NDDs) are a group of conditions that are clinically and etiologically heterogeneous. Biallelic variants inACBD6were previously reported in 7 patients with NDDs. Unfortunately, their clinical information remains very limited with descriptions of only their neurologic and craniofacial features. The purpose of this report is to expand the clinical phenotype of theACBD6-associated NDDs.MethodsWe identified 2 Thai siblings with NDDs. Clinical and radiologic features of the proband were described. The affected siblings and parents underwent whole-exome sequencing and PCR-Sanger sequencing.ResultsClinical manifestations that have never been previously reported include morbid obesity, pancytopenia with severe infections, diabetes mellitus, cirrhosis, and renal failure, leading to deaths in their early 30s. Molecular studies identified a novel homozygous 1 base-pair duplication (c.360dup; p.Leu121Thrfs*27) in theACBD6gene.DiscussionThis study reported 1 novel single base-pair duplication, expanding the mutational spectrum, and described the clinical features establishing the entity ofACBD6-associated NDDs.