Partial 21q monosomy due to 21q inversion and 21 chromosome ring: two case reports.

Backround: Children with multiple congenital anomalies (MCAs) are usually evaluated in the search of a known syndrome with chromosomal, monogenic or multifactorial causes. Aneuploidies of chromosome 21 are the most common chromosomal abnormalities in humans. 21q deletion syndrome is a very rare genetic disorder caused by missing of the genetic material in the long arm of chromosome 21 with variable clinical features. Aim: to report two cases of 21 deletion syndrome produced by two different mechanisms with variable clinical manifestations at early ages. Case 1: 10-year-old boy with growth retardation, intellectual disability, microcephaly, facial dysmorphism, joint stiffness, scoliosis. Karyotype 45, XY, -21. Mother with 46, XX, inv(21)(p12q22.1). On array we found partial 18p deletion and 21q deletion. Case 2: a boy with growth retardation, global developmental delay, microtia, short neck, scoliosis, hemivertebrae, interatrial communication. Array showed partial deletion 21q secondary to a 21-chromosome ring. Discussion: there are different mechanisms of 21 deletion syndrome and a variety of clinical manifestations and severity depending on the rearrangements and other chromosomes involved. Conclusion: both patients have growth retardation and intellectual disability, but differ in facial dysmorphisms and the presence of other congenital malformations such as cardiac and genitourinary. The correct approach of MCAs and intellectual disability allows to give an appropriate diagnosis and genetic counseling.