Homozygous loss of ADAM3A revealed by genome-wide analysis of pediatric high-grade glioma and diffuse intrinsic pontine gliomas

Abstract

Overall, pediatric high-grade glioma (pHGG) has a poor prognosis, in part due to the lack of understanding of the underlying biology. High-resolution 244 K oligo array comparative genomic hybridization (CGH) was used to analyze DNA from 38 formalin-fixed paraffin-embedded predominantly pretreatment pHGG samples, including 13 diffuse intrinsic pontine gliomas (DIPGs). The patterns of gains and losses were distinct from those seen in HGG arising in adults. In particular, we found 1q gain in up to 27% of our cohort compared with 9% reported in adults. A total of 13% had a balanced genetic profile with no large-scale copy number alterations. Homozygous loss at 8p12 was seen in 6 of 38 (16%) cases of pHGG. This novel deletion, which includes the ADAM3A gene, was confirmed by quantitative real-time PCR (qPCR). Loss of CDKN2A/CDKN2B in 4 of 38 (10%) samples by oligo array CGH was confirmed by fluorescent in situ hybridization on tissue microarrays and was restricted to supratentorial tumors. Only ∼50% of supratentorial tumors were positive for CDKN2B expression by immunohistochemistry (IHC), while ∼75% of infratentorial tumors were positive for CDKN2B expression (P = 0.03). Amplification of the 4q11-13 region was detected in 8% of cases and included PDGFRA and KIT, and subsequent qPCR analysis was consistent with the amplification of PDGFRA. MYCN amplification was seen in 5% of samples being significantly associated with anaplastic astrocytomas (P= 0.03). Overall, DIPG shared similar spectrum of changes to supratentorial HGG with some notable differences, including high-frequency loss of 17p and 14q and lack of CDKN2A/CDKN2B deletion. Informative genetic data providing insight into the underlying biology and potential therapeutic possibilities can be generated from archival tissue and typically small biopsies from DIPG. Our findings highlight the importance of obtaining pretreatment samples.

Fig. 1.

Ideogram showing all areas of gain and loss on chromosomes 1, 4, 14, and 17 in 25 HGG samples and 13 DIPGs. Red indicates regions of gain, and green indicates regions of loss.

Fig. 2.

Heatmap showing loss of 8p12 in 6 of the samples (green indicates regions of loss, red indicates regions of gain), and gene view showing specific loss of ADAM3A in 1 sample (probes in regions of loss are highlighted in green).

Fig. 3.

p16 FISH on pHGG TMAs: (A) sample with heterozygous loss of p16; (B) sample with homozygous loss of p16; (C) sample with normal copy of p16.

Fig. 4.

(A) Oligo aCGH profile showing amplification of MYCN in sample BSG9. (B) FISH showing high-level amplification of MYCN in sample BSG9. (C) Immunohistochemistry showing high nuclear expression of MYCN in sample BSG9.