AAV gene therapy for Batten disease

Posted by & filed under Part 16: LYSOSOMAL DISORDERS.

In this work, Beverly Davidson’s group investigated delivery of the gene encoding the soluble lysosomal enzyme tripeptidyl peptidase 1 (TPP1) enzyme to the ependymal cells in a dog model of a Batten disease.  They show that this strategy delayed disease onset, extended life span, and protected dogs from early cognitive decline, suggesting that this approach could improve the lives of children suffering from the same or similar diseases.

http://stm.sciencemag.org/content/7/313/313ra18

Posted by Nicola Brunetti-Pierri

Somatic mutation in single human brain cells

Posted by & filed under Exome sequencing, Part 03: GENERAL THEMES, Part 28: NEUROGENETICS.

Neurons live for decades in a postmitotic state and their genomes are susceptible to DNA damage. Using genome sequencing for individual human brain cells (postmortem), Lodato et al. have searched for somatic single-nucleotide variants (SNVs) in the human brain. After sequencing 36 neurons from the cerebral cortex of three normal individuals, they demonstrated that the average human neuron carries 1700 mutations.

Most of these mutations were unique to single neurons, rather than present in all cells, suggesting that most brain mutations arise after the brain has fully formed. Also, unlike germline and cancer SNVs, which are often caused by errors in DNA replication, in this study mutations were enriched in genes involved in neural function and development and are thought to have happened during gene transcription.

Somatic mutation in single human neurons tracks developmental and transcriptional history. Lodato et al. Science. 2015 Oct 2;350(6256):94-8.

Posted by Yannis Trakadis, MD

iINDs and inborn errors of metabolism

Posted by & filed under Treatment.

In the recent edition of Molecular Genetics and Metabolism, P. Dickson and J. Tolar discuss the potential of individual investigational new drug applications (iINDs) for N-of-One therapeutic trials of experimental therapies in inborn errors of metabolism (Mol Gen Metab 116 (2015):1-3). They discuss “pros”: faster bench to bedside translation, treating life-threatening conditions with no other therapeutic options, and “cons”: introducing risk to drug approvals, diminish patient pools for larger, controlled studies.

In the end, my take-away from this commentary is that that iINDs should be approached with a cautious optimism in carefully selected therapeutics for patients for inborn errors of metabolism. I also feel strongly that results of these N-of-One therapeutic trials, whether effective or not, should be made available to the metabolic community to guide further therapeutic decision making.

Hilary Vernon, MD PhD

ACVR1 R206H receptor mutation: a “gain of function” mutation cause of fibrodysplasia ossificans progressiva

Posted by & filed under Part 22: CONNECTIVE TISSUE.

Hatsell et al (Sci Transl Med. 2015 Sep 2;7(303):303ra137. doi: 10.1126/scitranslmed.aac4358) recently published very exciting work on the mechanism of the common ACVR1 gene mutation underlying fibrodysplasia ossificans progressive (FOP). This mutation confers the ability of the BMP 1 receptor ACVR1 to respond to  the inflammatory response ligand Activin A, and induce bone formation. This mechanism explains why individuals with FOP are not born with heterotopic bone, but develop this over time and characteristically after trauma.

This offers a novel directed mechanism of treatment, in that mice with a conditional ACVR1 R206H can be spared from heterotopic bone formation via introduction of an antibody directed at ActivinA1.

Hilary Vernon, MD PhD

 

Heimler Syndrome: a mild peroxisome biogenesis disorder

Posted by & filed under Part 15: PEROXISOMES.

Peroxisome biogenesis disorders are generally considered to be severe multisystem disorders, often with a progressive component. However, Ratbi et al, in the recent edition of American Journal of Human Genetics (2015 (97): 535-545) report that Heimler Syndrome, a disorder of hearing loss, abnormal dentition and nails, with or without retinitis pigmentosa, is due to hypomorphic alleles of the peroxisomal genes PEX1 and PEX6. The responsible genes were uncovered using whole exome sequencing in 7 families, and biochemically characterized via functional peroxisome testing of patient derived fibroblasts.

This is an excellent example of the marriage of both molecular and biochemical techiques to prove genetic causation of an inborn error of metabolism.

Hilary Vernon, MD PhD

Phase 3 Trial in Lysosomal Acid Lipase Deficiency

Posted by & filed under Part 12: LIPIDS, Treatment.

 

Lysosomal  acid lipase deficiency can cause cirrhosis and severe dyslipidemia. Burton et al. recently published in N Engl J Med a multicenter, randomized, double-blind, placebo-controlled study involving 66 patients with lysosomal acid lipase deficiency. This was a phase 3 clinical trial of enzyme-replacement therapy in children and adults, using sebelipase alfa.

Sebelipase alfa was administered intravenously (1 mg per kg; every other week) and the primary end point was normalization of the alanine aminotransferase level. Secondary end points included, lipid levels, fat content, as well as, safety and side-effect profile. The placebo-controlled phase of the study was 20 weeks long and was followed by open-label treatment for all patients.

A total of 65 of the 66 patients who underwent randomization completed the trial. At 20 weeks, the alanine aminotransferase level was normal in 11 of 36 patients (31%) in the sebelipase alfa group and in 2 of 30 (7%) in the placebo group (P=0.03). Lipid levels and hepatic fat content improved (P<0.001) for all comparisons, except for triglycerides (P=0.04). No adverse events related to treatment were identified.

A Phase 3 Trial of Sebelipase Alfa in Lysosomal Acid Lipase Deficiency. Burton BK et al. N Engl J Med. 2015 Sep 10;373(11):1010-20. doi: 10.1056/NEJMoa1501365. PMID: 26352813

Posted by Yannis Trakadis, MD

Post-zygotic Point Mutations

Posted by & filed under Part 06: DIAGNOSTIC APPROACHES.

My general practice in counseling families with a  child who has a suspected “de novo” dominant disorder is to estimate an approximate 5% recurrence risk for their future children based on potential gonadal mosaicism in the parents.

However, a recent paper by Acuna-Hidalgo et al (AJHG, Volume 97, Issue 1, p67–74, 2 July 2015) presented work in which they found that 6.5% of de novo mutations were actually present as mosaic mutations in the blood of the affected individual, and therefore likely happened post-zygotically.

If detection of this low level mosaicism were routinely available, this would significantly improve estimates of risk for parental gonadal mosaicism.

Hilary Vernon, MD PhD

Propofol use in methylmalonic acidemia

Posted by & filed under Part 09: ORGANIC ACIDS.

Our department’s general practice when advising on patients with organic acidemias who require surgery is to avoid the use of propofol. This practice was developed after a patient with methylmalonic acidemia (MMA) developed pancreatitis after a surgical procedure during which profofol was administered.

However a recent review of the anesthesia administration in a cohort of 28 patients with MMA or defects of cobalamin metabolism requiring 39 sedated procedures/surgeries showed that, in the setting of metabolic stability, propofol was administered safely. (Ktena et al, JIMD, 2015, Volume 38, Issue 5, pp 847-853).

This has caused me to reconsider my practice of absolutely recommending against propofol in MMA in the setting of a metabolically stable patient requiring an elective procedure.

Hilary Vernon, MD PhD

Losartan therapy for dystrophic epidermolysis bullosa

Posted by & filed under Part 27: SKIN.

Genetic loss of collagen VII causes recessive dystrophic epidermolysis bullosa (RDEB)—a severe skin fragility disorder associated with lifelong blistering and disabling progressive soft tissue fibrosis. No effective therapies are available. Based on the findings that TGF-beta activity is elevated in injured RDEB skin, Nystrom and colleagues targeted TGF-beta activity with losartan in RDEB mice. Long-term treatment with losartan reduced TGF-beta signaling in chronically injured forepaws and halted fibrosis and subsequent fusion of the digits. Losartan reduced inflammation and diminished TNF-alfa and IL-6 expression in injured forepaws. Collectively, the data argue that RDEB fibrosis is a consequence of a cascade encompassing tissue damage, TGF-beta-mediated inflammation, and matrix remodeling. The authors concluded that inhibition of TGF-beta activity limits these unwanted outcomes and thereby  ameliorates the disease phenotype.

http://onlinelibrary.wiley.com/doi/10.15252/emmm.201505061/abstract

Posted by Nicola Brunetti-Pierri, MD

AAV2-related insertional mutagenesis in human hepatocellular carcinomas: implications for gene therapy

Posted by & filed under Part 02: PERSPECTIVES.

Adeno-associated viral (AAV) vectors have been increasingly used for gene therapy in preclinical and clinical studies. In liver-directed approaches the AAV vectors have emereged as the most promising gene transfer vector in terms of safety and efficacy. A few studies have found increased incidence of hepatocellular carcinomas (HCCs) in mice injected with AAV vectors as newborns whereas no evidence of insertional mutagenesis and cancer were observed in adult mice, in dogs, and in nonhuman primates. In mice which developed cancer the AAV integrated in the Mir341 within the Rian locus that has no orthologues in the human genome.

A recent study published in Nature Genetics found clonal integration of AAV2 in 11 of 193 HCCs. These AAV2 integrations occurred in known cancer driver genes (CCNA2, TERT, CCNE1, TNFSF10, and KMT2B) leading to overexpression of the target genes. Tumors with viral integration mainly developed in non-cirrhotic liver (9 of 11 cases) and without known risk factors (6 of 11 cases), suggesting a pathogenic role for AAV2 in these patients. The authors concluded that AAV2 is a DNA virus associated with oncogenic insertional mutagenesis in human HCC.

This paper add important information of the controversial issue of AAV and insertional carcinogenesis and will affect development and design of gene therapy trials with AAV vectors.

http://www.nature.com/ng/journal/vaop/ncurrent/full/ng.3389.html

Posted by Nicola Brunetti-Pierri, MD