Had it begun five years earlier, Leo Le Gal\u2019s story would have followed a depressingly familiar pattern. Aged somewhere between 8 and 11, Leo would lose the ability to walk and go into a wheelchair. In his teens, he\u2019d progressively lose the use of his arms and with them, his independence. And eventually, some time between the ages of 21 and 30, his heart and lungs would give out, causing him to suffocate. But today there is a tantalising hope.<\/p>\n
Leo\u2019s parents, Ruth and Damien, got him onto a clinical trial for a drug that promises a reprieve. It\u2019s one of three drugs that are trying a totally new approach: directly treating the genetic problem that causes his disease, Duchenne muscular dystrophy (DMD), rather than simply treating its symptoms. Trials like Leo\u2019s have sent parents scrambling to get their sons on them and have brought the drugs to the threshold of widespread availability. Yet if he weren\u2019t already involved, the drug would probably remain out of reach for him, as it is for most of the 250,000 boys with DMD worldwide.<\/p>\n
Leo\u2019s condition occurs because he\u2019s a boy. As a woman, his mother has two X chromosomes, but one has a flaw in the gene carrying instructions for making a protein called dystrophin. Dystrophin sits inside muscle fibre cells and normally helps to hold them together, but the gene for its creation is one of the longest we have and is therefore susceptible to random mutations.<\/p>\n
As a boy, Leo inherits one of Ruth\u2019s X chromosomes and pairs it with his father Damien\u2019s Y chromosome. Ruth \u2013 with her two X chromosomes \u00ad\u2013 is unaffected by her faulty dystrophin gene because she has a spare; Leo, who has inherited the flawed gene, has no backup. This pattern means that usually only boys have DMD.<\/p>\n
The long dystrophin gene makes a large, complex protein that would be unable to get into muscle fibre cells from the outside, meaning the protein itself can\u2019t be a treatment. Instead, steroids have long been the main therapy, boosting what muscle remains and providing better breathing and a healthier heart. But steroids come with a long list of side-effects, making them despised by the Le Gals and other DMD families.<\/p>\n
The most obvious side-effect is a round-shaped face, caused by a build-up of the hormone cortisol that encourages fat deposits there and elsewhere throughout the body. The other side-effects include osteoporosis, which gives boys extremely weak bones, and cataracts. In addition, steroid treatment only slows the progressive muscle wasting. When their breathing muscles get too weak, boys with DMD go on ventilation machines, which can add at least ten years to their lives.<\/p>\n
By the time Leo\u2019s DMD was confirmed in 2011, the New Jersey-based company PTC Therapeutics had already been testing a drug treatment in boys for nearly six years. When testing whether DMD drugs work, the most important measurement is currently how far recipients can walk in six minutes. In one trial, conducted between February 2008 and December 2009, boys given one dosage for 48 weeks could walk 31 metres further on average than others who\u2019d been on an inactive placebo for the same time. \u201cIn the patients who were walking less than 350\u00a0m, we saw a greater than 68\u00a0m difference in change in distance walked versus placebo,\u201d says the CEO of PTC, Stuart Peltz. \u201cThat is one of the largest changes ever seen in the six-minute walk test in a clinical trial.\u201d<\/p>\n
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