Developmental delay and brain anomalies leading to significant morbidity and mortality are frequently caused by chromosomal rearrangements. We report on a familial unbalanced translocation resulting in distal monosomy 5p15.3-pter with trisomy 12q24.2-qter in 2 half siblings with cerebral dysgenesis, severe intellectual disability, dysmorphic features, progressive weakness, and atrophy of muscles.