1. Ornithine transcarbamylase deficiency: the story of Jesse Gelsinger

2. Jesse Gelsinger First person to die as a result of a gene therapy clinical trial Died 17 September 1999 aged 18 Jesse had partial ornithine transcarbamylase deficiency (OTC deficiency) Entered trial at Institute of Human Gene Therapy at the University of Pennsylvania 13 September: was administered functional OTC gene delivered by attenuated adenovirus via injection into hepatic artery Developed a severe immune reaction to the adenovirus and died 4 days later Investigations revealed ethical, technical and regulatory issues – lack of informed consent! (Previous trial participants experienced severe side effects, and 3 monkeys had died during preclinical phase). FDA has since suspended a further 13 gene therapy trials and introduced a new Gene Therapy Clinical Trial Monitoring Plan www.Jesse-Gelsinger.com

3. Gene therapy Principle: deliver a ‘therapeutic’ gene into target cells lacking or abnormally expressing that gene (e.g. genetic disorders) Gene is integrated into genome  normal protein expression  cell function Adenoviral vector Vehicle for gene Efficient nuclear entry Low pathogenicity Viral nucleic acid does not integrate into genome Widely used in basic research, gene therapy trials and vaccine development Adverse reactions (as in Jesse’s case) very rare! Cancer Information Centre, 2013

4. What is OTC deficiency? Rare genetic disorder (1 in 80,000) X-linked: on X chromosome, passed on only by mothers Recessive: two copies of mutant gene (homozygous)  OTC deficiency. One copy of mutant gene (heterozygous) in XX females does not cause disease and is lethal in XY males (only 1 X!) Hence, cannot be passed on by fathers >200 mutations in OTC gene Encodes enzyme participating in urea cycle Loss of function: Truncated protein Abnormally folded protein No protein  DISEASE X Chromosome: p21.1 Children’s National Medical Centre, 2007

5. Urea cycle Metabolic cascade in liver Processes excess ammonia from protein breakdown and converts it into urea (to be excreted by kidneys) Initiates in mitochondria and continues in cytosol OTC catalyzes conversion of L- ornithine + carbamyl phosphate to citrulline OTC deficiency: inefficiency or absence of this step  accumulation of ammonia in the blood  toxicity (especially CNS)  severe neurological deficits Lam Tat Chung, 2008 National Toxicology Program, 2014 Diagram Resources, 2014

6. Clinical features and management Lethargy, lack of appetite, dysregulated temperature and ventilation. Severe symptoms: seizures, ataxia and coma Commonly presenting ~ 72 hrs after birth >50 % cases die within a month In some cases (such as Jesse’s), less severe symptoms present later in life Diagnosis: Blood (high ammonia, low citrulline), urine (high orotic acid), genetic screen for OTC mutation and liver enzyme activity check Management: Referral to nutritionist Low protein diet and supplements Dialysis Genetic counselling and support services Reduce blood ammonia