Anticipatory banking of samples enables diagnosis of adenylosuccinase deficiency following molecular autopsy in an infant with vacuolating leukoencephalopathy.

Adenylosuccinase deficiency is a rare inborn error of metabolism. We present a newborn who died at 52 days of age with clinical features suggestive of severe epileptic encephalopathy and leukodystrophy of unknown cause. Post-mortem examination showed an unusual vacuolar appearance of the brain. A molecular autopsy performed via singleton clinical exome analysis revealed a known pathogenic and a variant of uncertain significance in ADSL that encodes adenylosuccinase. Tests on previously stored plasma samples showed elevated succinyladenosine and succinylaminoimidazole carboxamide riboside levels. Adenylosuccinase activity in stored fibroblasts was only ~5% of control confirming the diagnosis of adenylosuccinase deficiency in the child. The parents opted for a chorionic villus biopsy in a subsequent pregnancy and had a child unaffected by adenylosuccinase deficiency. This report adds vacuolating leukodystrophy as a novel feature of adenylosuccinase deficiency and shows the power of biochemical investigations directed by genomic studies to achieve accurate diagnosis. Importantly, this case demonstrates the importance of anticipatory banking of biological samples for reverse biochemical phenotyping in individuals with undiagnosed disorders who may not survive.

Personalised virtual gene panels reduce interpretation workload and maintain diagnostic rates of proband-only clinical exome sequencing for rare disorders.

PURPOSE: The increased adoption of genomic strategies in the clinic makes it imperative for diagnostic laboratories to improve the efficiency of variant interpretation. Clinical exome sequencing (CES) is becoming a valuable diagnostic tool, capable of meeting the diagnostic demand imposed by the vast array of different rare monogenic disorders. We have assessed a clinician-led and phenotype-based approach for virtual gene panel generation for analysis of targeted CES in patients with rare disease in a single institution. METHODS: Retrospective survey of 400 consecutive cases presumed by clinicians to have rare monogenic disorders, referred on singleton basis for targeted CES. We evaluated diagnostic yield and variant workload to characterise the usefulness of a clinician-led approach for generation of virtual gene panels that can incorporate up to three different phenotype-driven gene selection methods. RESULTS: Abnormalities of the nervous system (54.5%), including intellectual disability, head and neck (19%), skeletal system (16%), ear (15%) and eye (15%) were the most common clinical features reported in referrals. Combined phenotype-driven strategies for virtual gene panel generation were used in 57% of cases. On average, 7.3 variants (median=5) per case were retained for clinical interpretation. The overall diagnostic rate of proband-only CES using personalised phenotype-driven virtual gene panels was 24%. CONCLUSIONS: Our results show that personalised virtual gene panels are a cost-effective approach for variant analysis of CES, maintaining diagnostic yield and optimising the use of resources for clinical genomic sequencing in the clinic.

Constitutional de novo deletion CNV encompassing REST predisposes to diffuse hyperplastic perilobar nephroblastomatosis (HPLN).

BACKGROUND: Nephroblastomatosis is a recognised precursor for the development of Wilms tumour (WT), the most common childhood renal tumour. While the majority of WT is sporadic in origin, germline intragenic mutations of predisposition genes such as WT1, REST and TRIM28 have been described in apparently isolated (non-familial) WT.Despite constitutional CNVs being a well-studied cause of developmental disorders, their role in cancer predisposition is less well defined, so that the interpretation of cancer risks associated with specific CNVs can be complex. OBJECTIVE: To highlight the role of a constitutional deletion CNV (delCNV) encompassing the REST tumour suppressor gene in diffuse hyperplastic perilobar nephroblastomatosis (HPLN). METHODS/RESULTS: Array comparative genomic hybridisation in an infant presenting with apparently sporadic diffuse HPLN revealed a de novo germline CNV, arr[GRCh37] 4q12(57,385,330-57,947,405)x1. The REST tumour suppressor gene is located at GRCh37 chr4:57,774,042-57,802,010. CONCLUSION: This delCNV encompassing REST is associated with nephroblastomatosis. Deletion studies should be included in the molecular work-up of inherited predisposition to WT/nephroblastomatosis. Detection of delCNVs involving known cancer predisposition genes can yield insights into the relationship between underlying genomic architecture and associated tumour risk.

Chromosome 1q31.2q32.1 deletion in an adult male with intellectual disability, dysmorphic features and obesity.

Intermediate interstitial deletions of the long arm of chromosome 1 are typically associated with developmental delay and dysmorphic features. We describe the case of a 31-year-old male with intellectual disability, obesity and dysmorphic features, in whom array-comparative genomic hybridization identified a de novo 9.55 Mb deletion at 1q31.2q32.1. We discuss the genes encompassed within the deleted region; in particular, the implications of the deleted cancer-predisposing gene, CDC-73, and compare our clinical findings to other cases with similar deletions. The absence of microcephaly and growth retardation appears to differentiate more proximal interstitial 1q deletions from intermediate 1q deletions, and the presence of obesity is a newly reported phenotype within the 1q deletion spectrum. It is imperative that surveillance for CDC-73 related disorders, including parathyroid carcinoma, is considered in the management of interstitial intermediate 1q deletions.