Detection of an Underlying 22q11.2 Duplication in a Female Neonate With Trisomy 18

Current guidelines indicate that in patients with developmental disabilities or congenital anomalies, chromosomal microarray (CMA) is a first-tier diagnostic test. However, for patients with obvious chromosomal syndromes such as trisomy 13, 18, and 21, G-banded karyotyping is still recommended over CMA for establishing a diagnosis. In the case presented herein, a female neonate was suspected of having trisomy 18 based on pre- and postnatal evaluations. Karyotyping was requested but not performed due to insufficient cell growth; Interphase fluorescence in situ hybridization (i-FISH) found an extra copy of chromosome 18. CMA analysis uncovered gain of chromosome 18 and an additional duplication in chromosome 22q11.2, which went undetected with FISH. Our patient died within 40 hours after birth, but it is expected that patients with recognizable chromosomal syndromes could benefit from the discovery of coexisting copy number variations (CNVs) using CMA. This case shows that CMA can be a useful test for patients with recognizable chromosomal syndromes because of the potential benefits for patients and their families when co-existing CNVs are found.