Ring chromosome 21 syndrome is an autosomal anomaly characterized by variable clinical features, most commonly including growth retardation, developmental delay, intellectual disability, epilepsy, microcephaly, short stature, dysmorphic features, hypogammaglobulinemia, thrombocytopenia and unspecific skeletal anomalies (hemivertebrae, clinodactyly, syndactyly). In rare cases, it has been described in phenotypically normal individuals. The disease is MONDO_0015437 (ring chromosome 21). Also known as: Chromosome 21 Ring, Ring chromosome type 21, chromosome 21 en anneau.