Chromosomal microarray (CMA) is increasingly utilized for genetic testing of individuals with unexplained developmental delay/intellectual disability (DD/ID), autism spectrum disorders (ASD), or multiple congenital anomalies (MCA). Performing CMA and G-banded karyotyping on every patient substantially increases the total cost of genetic testing. The International Standard Cytogenomic Array (ISCA) Consortium held two international workshops and conducted a literature review of 33 studies, including 21,698 patients tested by CMA. We provide an evidence-based summary of clinical cytogenetic testing comparing CMA to G-banded karyotyping with respect to technical advantages and limitations, diagnostic yield for various types of chromosomal aberrations, and issues that affect test interpretation. CMA offers a much higher diagnostic yield (15%-20%) for genetic testing of individuals with unexplained DD/ID, ASD, or MCA than a G-banded karyotype ( approximately 3%, excluding Down syndrome and other recognizable chromosomal syndromes), primarily because of its higher sensitivity for submicroscopic deletions and duplications. Truly balanced rearrangements and low-level mosaicism are generally not detectable by arrays, but these are relatively infrequent causes of abnormal phenotypes in this population (<1%). Available evidence strongly supports the use of CMA in place of G-banded karyotyping as the first-tier cytogenetic diagnostic test for patients with DD/ID, ASD, or MCA. G-banded karyotype analysis should be reserved for patients with obvious chromosomal syndromes (e.g., Down syndrome), a family history of chromosomal rearrangement, or a history of multiple miscarriages.

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Double minutes (dmin) and homogeneously staining regions (hsr) are the cytogenetic hallmarks of genomic amplification in cancer. Different mechanisms have been proposed to explain their genesis. Recently, our group showed that the MYC-containing dmin in leukemia cases arise by excision and amplification (episome model). In the present paper we investigated 10 cell lines from solid tumors showing MYCN amplification as dmin or hsr. Particularly revealing results were provided by the two subclones of the neuroblastoma cell line STA-NB-10, one showing dmin-only and the second hsr-only amplification. Both subclones showed a deletion, at 2p24.3, whose extension matched the amplicon extension. Additionally, the amplicon structure of the dmin and hsr forms was identical. This strongly argues that the episome model, already demonstrated in leukemias, applies to solid tumors as well, and that dmin and hsr are two faces of the same coin. The organization of the duplicated segments varied from very simple (no apparent changes from the normal sequence) to very complex. MYCN was always overexpressed (significantly overexpressed in three cases). The fusion junctions, always mediated by nonhomologous end joining, occasionally juxtaposed truncated genes in the same transcriptional orientation. Fusion transcripts involving NBAS (also known as NAG), FAM49A, BC035112 (also known as NCRNA00276), and SMC6 genes were indeed detected, although their role in the context of the tumor is not clear.

In childhood malignancies such as retinoblastoma and Wilms tumour, of which both familial and sporadic forms exist, recessive mutations of presumed differentiation genes have been implicated in tumorigenesis. A proportion of cases appear with microscopically visible chromosome deletions which indicate the regions where the genes concerned are located. Mutation or loss of one allele causes a cancer predisposition. For tumour development functional loss of the remaining normal allele is also required. In cancers with both familial and sporadic forms, molecular-genetic studies have shown that deletion is often one of the mutational events. Although familial and sporadic forms have never been distinguished in lung cancer, deletions of the short arm of chromosome 3 have been described for small cell lung cancer (SCLC), but their general occurrence in SCLC has been disputed. Using a molecular-genetic approach, we here present evidence for a consistent deletion at the chromosomal region 3p21, not only in SCLC, but in all major types of lung cancer.

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Sporadic clear cell renal cell carcinoma (cRCC) is genetically characterized by the recurrent loss of the short arm of chromosome 3, with a hotspot for copy number loss in the 3p21 region. We applied a method called "gene identification by nonsense-mediated mRNA decay inhibition" to a panel of 10 cRCC cell lines with 3p21 copy number loss to identify biallelic inactivated genes located at 3p21. This revealed inactivation of the histone methyltransferase gene SETD2, located on 3p21.31, as a common event in cRCC cells. SETD2 is nonredundantly responsible for trimethylation of the histone mark H3K36. Consistent with this function, we observed loss or a decrease of H3K36me3 in 7 out of the 10 cRCC cell lines. Identification of missense mutations in 2 out of 10 primary cRCC tumor samples added support to the involvement of loss of SETD2 function in the development of cRCC tumors. Cancer Res; 70(11); 4287-91. ©2010 AACR.

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In the past decade important progress has been made in our understanding of the epigenetic regulatory machinery. It has become clear that genetic aberrations in multiple epigenetic modifier proteins are associated with various types of cancer. Moreover, targeting the epigenome has emerged as a novel tool to treat cancer patients. Recently, the first drugs have been reported that specifically target SETD2-negative tumors. In this review we discuss the studies on the associated protein, Set domain containing 2 (SETD2), a histone modifier for which mutations have only recently been associated with cancer development. Our review starts with the structural characteristics of SETD2 and extends to its corresponding function by combining studies on SETD2 function in yeast, Drosophila, Caenorhabditis elegans, mice, and humans. SETD2 is now generally known as the single human gene responsible for trimethylation of lysine 36 of Histone H3 (H3K36). H3K36me3 readers that recruit protein complexes to carry out specific processes, including transcription elongation, RNA processing, and DNA repair, determine the impact of this histone modification. Finally, we describe the prevalence of SETD2-inactivating mutations in cancer, with the highest frequency in clear cell Renal Cell Cancer, and explore how SETD2-inactivation might contribute to tumor development.