Implications of a Chr7q21.11 microdeletion and the role of the PCLO gene in developmental delay

We report here a 4-year-old boy with global developmental delay who was referred for karyotyping and fragile X studies. A small interstitial deletion on chromosome 7 at band 7q21 was detected in all cells examined. Subsequent molecular karyotype analysis gave the more detailed result of a 6.3 Mb heterozygous deletion involving the interstitial chromosome region 7q21.11. In this relatively gene-poor region, the presynaptic cytomatrix protein, Piccolo [PCLO] gene appears to be the most likely candidate for copy number loss leading to a clinical phenotype. G-banded chromosome analysis of the parents showed this deletion was inherited from the father. Molecular karyotype analysis of the father's genome confirmed that it was the same deletion as that seen in the son; however, the father did not share the severity of his son's phenotype. This cytogenetically-visible deletion may represent another example of a chromosomal rearrangement conferring a variable phenotype on different family members

Clinical outcomes and counseling issues regarding partial trisomy of terminal Xp in a child with developmental delay

Female carriers of balanced translocations involving an X chromosome and an autosome present genetic councelling challenges. This is in view of the number of possible meiotic outcomes, but also due to the impact of X chromosome-localised genes that are no longer subject to gene silencing through the X chromosome inactivation centre. We present a case where delineation of the extent of X chromosome-localised genes on the derivative autosome using molecular karyotyping offers critical information in the context of genetic councelling

Array-based identification of copy number changes in a diagnostic setting. Simultaneous gene-focused and low resolution whole human genome analysis

The aim of this study was to develop and validate a comparative genomic hybridisation [CGH] array that would allow simultaneous targeted analysis of a panel of disease genes and low resolution whole genome analysis. A bespoke Roche NimbleGen 12x135K CGH array [Roche NimbleGen Inc., Madison, Wisconsin, USA] was designed to interrogate the coding regions of 66 genes of interest, with additional widelyspaced backbone probes providing coverage across the whole genome. We analysed genomic deoxyribonucleic acid [DNA] from 20 patients with a range of previously characterised copy number changes and from 8 patients who had not previously undergone any form of dosage analysis. The custom-designed Roche NimbleGen CGH array was able to detect known copy number changes in all 20 patients. A molecular diagnosis was also made for one of the additional 4 patients with a clinical diagnosis that had not been confirmed by sequence analysis, and carrier testing for familial copy number variants was successfully completed for the remaining four patients. The custom-designed CGH array described here is ideally suited for use in a small diagnostic laboratory. The method is robust, accurate, and cost-effective, and offers an ideal alternative to more conventional targeted assays such as multiplex ligation-dependent probe amplification