Mondo Description Monosomy 13q34 is a rare chromosomal anomaly syndrome, resulting from the partial deletion of the long arm of chromosome 13, principally characterized by global developmental delay, mild intellectual disability, obesity and mild craniofacial dysmorphism (microcephaly, wide rectangular forehead, downslanting palpebral fissures, mild ptosis, prominent nose with long nasal bridge and broad tip, small chin). Other variable reported features include congenital heart defects, hand and foot anomalies (e.g. polydactyly) and agenesis of the corpus callosum.