NSMCE3 and Immunodeficiency: Here, we identify homozygous and compound heterozygous missense mutations in NSMCE3 as the cause of what we believe to be a new autosomal recessive chromosome breakage syndrome, characterized by failure to thrive, absent (or mild) dysmorphic features, immune deficiency, and severe and eventually fatal pediatric pulmonary disease, initially resembling PARDS, in early childhood.