Outcomes From Whole-Brain Reirradiation Using Pulsed Reduced Dose Rate Radiation Therapy.

PURPOSE: Recurrent intracranial metastases after whole-brain irradiation pose a clinical challenge owing to the escalating morbidity associated with their treatment. Although stereotactic radiosurgery is increasingly being used, there are still situations in which whole-brain reirradiation (ReRT) continues to be appropriate. Here, we report our experience using whole-brain pulsed reduced dose rate radiation therapy (PRDR), a method that delivers radiation at a slower rate of 0.067 Gy/min to potentially increase sublethal damage repair and decrease toxicity. METHODS AND MATERIALS: Patients undergoing whole-brain ReRT with PRDR from January 1, 2001 to March 2019 were analyzed. The median PRDR ReRT dose was 26 Gy in 2 Gy fractions, resulting in a median total whole-brain dose of 59.5 Gy. Cox regression analysis was used for multivariate analysis. The Kaplan-Meier method was used for overall survival, progression free survival, and to evaluate the ReRT score. Binary logistic regression was employed to evaluate variables associated with rapid death. RESULTS: Seventy-five patients were treated with whole-brain PRDR radiation therapy. The median age was 54 (range, 26-72), the median Karnofsky performance status (KPS) was 80, and 86.7% had recursive partitioning analysis scores of 2. Thirty-two patients had over 10 metastases and 11 had leptomeningeal disease. The median overall survival was 4.1 months (range, 0.29-59.5 months) with a 1 year overall survival of 10.4%. Age, KPS, dexamethasone usage, and intracranial disease volume were significantly correlated with overall survival on multivariate analysis. A KPS ≤70 was associated with rapid death after radiation. The prognostic value of the ReRT score was validated. The most common acute toxicities were fatigue (23.1%) and headache (16.9%). CONCLUSIONS: In this large cohort of patients with advanced intracranial metastases, PRDR achieves acceptable survival and may decrease toxicity associated with ReRT. PRDR is an easily implemented technique and is a viable treatment option for ReRT of brain metastases.

Mutations in the Glycosyltransferase Domain of GLT8D1 Are Associated with Familial Amyotrophic Lateral Sclerosis.

Amyotrophic lateral sclerosis (ALS) is a severe neurodegenerative disorder without effective neuroprotective therapy. Known genetic variants impair pathways, including RNA processing, axonal transport, and protein homeostasis. We report ALS-causing mutations within the gene encoding the glycosyltransferase GLT8D1. Exome sequencing in an autosomal-dominant ALS pedigree identified p.R92C mutations in GLT8D1, which co-segregate with disease. Sequencing of local and international cohorts demonstrated significant ALS association in the same exon, including additional rare deleterious mutations in conserved amino acids. Mutations are associated with the substrate binding site, and both R92C and G78W changes impair GLT8D1 enzyme activity. Mutated GLT8D1 exhibits in vitro cytotoxicity and induces motor deficits in zebrafish consistent with ALS. Relative toxicity of mutations in model systems mirrors clinical severity. In conclusion, we have linked ALS pathophysiology to inherited mutations that diminish the activity of a glycosyltransferase enzyme.

Targeted Genetic Screen in Amyotrophic Lateral Sclerosis Reveals Novel Genetic Variants with Synergistic Effect on Clinical Phenotype.

Amyotrophic lateral sclerosis (ALS) is underpinned by an oligogenic rare variant architecture. Identified genetic variants of ALS include RNA-binding proteins containing prion-like domains (PrLDs). We hypothesized that screening genes encoding additional similar proteins will yield novel genetic causes of ALS. The most common genetic variant of ALS patients is a G4C2-repeat expansion within C9ORF72. We have shown that G4C2-repeat RNA sequesters RNA-binding proteins. A logical consequence of this is that loss-of-function mutations in G4C2-binding partners might contribute to ALS pathogenesis independently of and/or synergistically with C9ORF72 expansions. Targeted sequencing of genomic DNA encoding either RNA-binding proteins or known ALS genes (n = 274 genes) was performed in ALS patients to identify rare deleterious genetic variants and explore genotype-phenotype relationships. Genomic DNA was extracted from 103 ALS patients including 42 familial ALS patients and 61 young-onset (average age of onset 41 years) sporadic ALS patients; patients were chosen to maximize the probability of identifying genetic causes of ALS. Thirteen patients carried a G4C2-repeat expansion of C9ORF72. We identified 42 patients with rare deleterious variants; 6 patients carried more than one variant. Twelve mutations were discovered in known ALS genes which served as a validation of our strategy. Rare deleterious variants in RNA-binding proteins were significantly enriched in ALS patients compared to control frequencies (p = 5.31E-18). Nineteen patients featured at least one variant in a RNA-binding protein containing a PrLD. The number of variants per patient correlated with rate of disease progression (t-test, p = 0.033). We identified eighteen patients with a single variant in a G4C2-repeat binding protein. Patients with a G4C2-binding protein variant in combination with a C9ORF72 expansion had a significantly faster disease course (t-test, p = 0.025). Our data are consistent with an oligogenic model of ALS. We provide evidence for a number of entirely novel genetic variants of ALS caused by mutations in RNA-binding proteins. Moreover we show that these mutations act synergistically with each other and with C9ORF72 expansions to modify the clinical phenotype of ALS. A key finding is that this synergy is present only between functionally interacting variants. This work has significant implications for ALS therapy development.