||Recently, 3 unrelated children with a potentially novel 3q26.33-3q27.2 microdeletion syndrome were reported. We now report a new 9 ½ years old Caucasian boy with a 2 Mb deletion of the same genomic region in combination with Klinefelter syndrome. He presented with facial dysmorphism, developmental delay, Asperger syndrome, thrombocytopenia, recurrent infections and hypogammaglobulinemia. The deletion in our patient improves upon the minimum region of the novel 3q26.33-3q27.2 microdeletion, and provides additional insights into the underlying genetic basis of the observed phenotypes. Consistent with two of three previously described patients, our patient also presents with thrombocytopenia, which we postulate is caused by haploinsufficiency of THPO. In addition, haploinsufficiency of LAMP3, a lymphoid and dendritic cell expressed protein that is implicated in bacterial and viral infections, pulmonary surfactant protein transport and amelogenin degradation, may be a novel cause for the immune deficiency, lung disease and dental abnormalities respectively as seen in these patients.