Array comparative genomic hybridization (aCGH) is now widely adopted as a first-tier clinical diagnostic test for patients with developmental delay (DD)/intellectual disability (ID), autism spectrum disorders, and multiple congenital anomalies. Nevertheless, classic karyotyping still has its impact in diagnosing genetic diseases, particularly mosaic cases.
We report on a 30 year old patient with syndromic intellectual disability, a 22q13.2 microdeletion and mosaic trisomy 22. The patient had the following clinical features: intrauterine growth retardation at birth, hypotonia, cryptorchidism, facial asymmetry, enophthalmus, mild prognathism, bifid uvula, hypoplastic upper limb phalanges, DD including speech delay, and ID. Whole genome aCGH showed a de novo 1 Mb interstitial heterozygous deletion in 22q13.2, confirmed by fluorescence in situ hybridization in all cells examined. Moreover, 18% cells had an extra chromosome 22 suggesting a trisomy 22 mosaicism.
Almost all 22q13 deletions published so far have been terminal deletions with variable sizes (100 kb to over 9 Mb). Very few cases of interstitial 22q13.2 deletions were reported. In its mosaic form, trisomy 22 is compatible with life, and there are about 20 reports in the literature. It has a variable clinical presentation: growth restriction, dysmorphic features, cardiovascular abnormalities, hemihyperplasia, genitourinary tract anomalies and ID. Neurodevelopmental outcome ranges from normal to severe DD. The patient presents clinical features that are common to both the interstitial 22q13 deletion and the mosaic trisomy 22; characteristics related to the interstitial deletion alone and others explained solely by the mosaic trisomy.
Our case points out the role of conventional cytogenetic tools in mosaic cases that could be missed by microarray technology. We therefore suggest the combination of both conventional and molecular karyotyping in the investigation of certain genetic diseases.