DNA replication-associated mutations are repaired by two components: polymerase proofreading and mismatch repair. The mutation consequences of disruption to both repair components in humans are not well studied. We sequenced cancer genomes from children with inherited biallelic mismatch repair deficiency (bMMRD). High-grade bMMRD brain tumors exhibited massive numbers of substitution mutations (>250/Mb), which was greater than all childhood and most cancers (>7,000 analyzed). All ultra-hypermutated bMMRD cancers acquired early somatic driver mutations in DNA polymerase ɛ or δ. The ensuing mutation signatures and numbers are unique and diagnostic of childhood germ-line bMMRD (P < 10(-13)). Sequential tumor biopsy analysis revealed that bMMRD/polymerase-mutant cancers rapidly amass an excess of simultaneous mutations (∼600 mutations/cell division), reaching but not exceeding ∼20,000 exonic mutations in <6 months. This implies a threshold compatible with cancer-cell survival. We suggest a new mechanism of cancer progression in which mutations develop in a rapid burst after ablation of replication repair.

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Purpose To uncover the genetic events leading to transformation of pediatric low-grade glioma (PLGG) to secondary high-grade glioma (sHGG). Patients and Methods We retrospectively identified patients with sHGG from a population-based cohort of 886 patients with PLGG with long clinical follow-up. Exome sequencing and array CGH were performed on available samples followed by detailed genetic analysis of the entire sHGG cohort. Clinical and outcome data of genetically distinct subgroups were obtained. Results sHGG was observed in 2.9% of PLGGs (26 of 886 patients). Patients with sHGG had a high frequency of nonsilent somatic mutations compared with patients with primary pediatric high-grade glioma (HGG; median, 25 mutations per exome; P = .0042). Alterations in chromatin-modifying genes and telomere-maintenance pathways were commonly observed, whereas no sHGG harbored the BRAF-KIAA1549 fusion. The most recurrent alterations were BRAF V600E and CDKN2A deletion in 39% and 57% of sHGGs, respectively. Importantly, all BRAF V600E and 80% of CDKN2A alterations could be traced back to their PLGG counterparts. BRAF V600E distinguished sHGG from primary HGG (P = .0023), whereas BRAF and CDKN2A alterations were less commonly observed in PLGG that did not transform (P < .001 and P < .001 respectively). PLGGs with BRAF mutations had longer latency to transformation than wild-type PLGG (median, 6.65 years [range, 3.5 to 20.3 years] v 1.59 years [range, 0.32 to 15.9 years], respectively; P = .0389). Furthermore, 5-year overall survival was 75% ± 15% and 29% ± 12% for children with BRAF mutant and wild-type tumors, respectively (P = .024). Conclusion BRAF V600E mutations and CDKN2A deletions constitute a clinically distinct subtype of sHGG. The prolonged course to transformation for BRAF V600E PLGGs provides an opportunity for surgical interventions, surveillance, and targeted therapies to mitigate the outcome of sHGG.

Neonatal diabetes can be either permanent or transient. We have recently shown that permanent neonatal diabetes can result from complete deficiency of glucokinase activity. Here we report three new cases of glucokinase-related permanent neonatal diabetes. The probands had intrauterine growth retardation (birth weight <1,900 g) and insulin-treated diabetes from birth (diagnosis within the first week of life). One of the subjects was homozygous for the missense mutation Ala378Val (A378V), which is an inactivating mutation with an activity index of only 0.2% of wild-type glucokinase activity. The second subject was homozygous for a mutation in the splice donor site of exon 8 (intervening sequence 8 [IVS8] ؉ 2T3 G), which is predicted to lead to the synthesis of an inactive protein. The third subject (second cousin of subject 2) was a compound heterozygote with one allele having the splice-site mutation IVS8 ؉ 2T3 G and the other the missense mutation Gly264Ser (G264S), a mutation with an activity index of 86% of normal activity. The five subjects with permanent neonatal diabetes due to glucokinase deficiency identified to date are characterized by intrauterine growth retardation, permanent insulin-requiring diabetes from the first day of life, and hyperglycemia in both parents. Autosomal recessive inheritance and enzyme deficiency are features typical for an inborn error of metabolism, which occurred in the glucose-insulin signaling pathway in these subjects. Diabetes 52: 2854 -2860, 2003 N eonatal diabetes, insulin-requiring hyperglycemia occurring within the first month of life is often associated with intrauterine growth retardation (IUGR) and can be either transient or permanent (1). Transient neonatal diabetes is associated with abnormalities of chromosome 6, including paternal uniparental disomy and paternal duplications of 6q24, with loss of imprinting (1,2) and increased risk of diabetes later in life. Mutations in the insulin promoter factor-1, a transcription factor implicated in pancreatic development and the regulation of insulin gene expression, result in permanent neonatal diabetes (PNDM) caused by pancreatic agenesis (3). We have recently shown that complete deficiency of the glycolytic enzyme glucokinase is another cause of PNDM (4). Two patients presented with IUGR, permanent insulin requirement from shortly after birth and homozygosity for mutations in the glucokinase gene (GCK). Here we present the results of screening eight cases of PNDM for mutations in glucokinase. Three of these had glucokinase-related PNDM, including a subject who inherited different inactivating mutations from each parent. RESEARCH DESIGN AND METHODSSubjects. The screening included eight cases of PNDM, defined as a diagnosis of permanent diabetes before age 1 month. The probands of families 1-3 were identified by one of the authors (P.R.N.) by a PubMed literature search, after which the corresponding authors (N.S. and S.U.S.) were contacted. The other PNDM patients were from the Department of Pediatrics, University of Be...

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The prevalence and penetrance of GI neoplasia in children with BMMRD is high, with rapid development of carcinoma. Colorectal and small bowel surveillance should commence at ages 3-5 and 8 years, respectively.

Biallelic mismatch repair deficiency (bMMRD) is a cancer predisposition syndrome affecting primarily individuals from consanguinous families resulting in multiple childhood cancers including high grade gliomas (HGG). This is the first study to assess the prevalence of bMMRD among patients with HGG in countries where consanguinity is high. We collected molecular and clinical information on all children diagnosed with HGG and supratentorial primitive neuroectodermal tumors (sPNET) between 2003 and 2013 at King Hussein Cancer Center, Jordan. Comparison was made to a similar cohort from Toronto. Clinical data regarding presence of caf e au lait macules(CAL), family history of cancer, consanguinity, pathology and treatment were collected. Tumors were centrally reviewed and tested for MMRD by immunohistochemistry of the corresponding proteins. Fortytwo patients fulfilled the inclusion criteria, including 36 with HGG. MMRD was observed in 39% of HGG of whom79% also lost MMR staining in the corresponding normal cells suggestive of bMMRD. P53 dysfunction was highly enriched in MMR deficient tumors (p 5 0.0003).The frequency of MMRD was significantly lower in Toronto cohort (23%, p 5 0.03). Both evidence of CAL and consanguinity correlated with bMMRD (p 5 0.005 and 0.05,respectively) but family history of cancer didn't. HGG with all three bMMRD risk factors had evidence of MMRD and all children affected by multiple bMMRD related cancers had identical gene loss by immunohistochemical staining. In Jordan, the frequency of clinical and immunohistochemical alterations suggestive of bMMRD in pediatric HGG is high. Genetic testing will enable appropriate counseling and cancer screening to improve survival of these patients.Biallelic mismatch repair deficiency (bMMRD) is an autosomal recessive cancer predisposition syndrome caused by a biallelic germline mutation in the DNA mismatch repair (MMR) genes. This is one of the most devastating cancer syndromes associated with high penetrance and mortality during childhood.1-3 The MMR genes which are known to cause this syndrome in humans are MLH1, MSH2, MSH6 and PMS2. In contrast to heterozygous carriers of mutations in these genes who are at risk to develop gastrointestinal and urogenital tumors as adults, 4,5 bMMRD is characterized by a broad spectrum of early onset tumors during childhood. The most common cancers affecting children are brain tumors followed by hematological malignancies and a variety of premalignant and malignant lesions of the gastrointestinal tract. High grade gliomas (HGG) are the most common CNS tumors associated with bMMRD and are the major cause of

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