Mondo Description Distal monosomy 3p is a rare chromosomal anomaly syndrome, resulting from a partial deletion of the short arm of chromosome 3, with a highly variable phenotype typically characterized by pre- and post-natal growth retardation, intellectual disability, developmental delay and craniofacial dysmorphism (microcephaly, trigonocephaly, downslanting palpebral fissures, telecanthus, ptosis, micrognathia). Postaxial polydactyly, hypotonia, renal anomalies and congenital heart defects (e.g. atrioventricular septal defect) may be associated.