Developments

GENE THERAPY

What is gene therapy?

Genes, which are carried on chromosomes, are the basic physical and functional units of heredity. Genes are specific sequences of bases that encode instructions on how to make proteins. Although genes get a lot of attention, it's the proteins that perform most life functions and even make up the majority of cellular structures. When genes are altered so that the encoded proteins are unable to carry out their normal functions, genetic disorders can result.

Gene therapy is a technique for correcting defective genes responsible for disease development. Researchers may use one of several approaches for correcting faulty genes:

• A normal gene may be inserted into a nonspecific location within the genome to replace a nonfunctional gene. This approach is most common.
• An abnormal gene could be swapped for a normal gene through homologous recombination.
• The abnormal gene could be repaired through selective reverse mutation, which returns the gene to its normal function.
• The regulation (the degree to which a gene is turned on or off) of a particular gene could be altered.

How does gene therapy work?

In most gene therapy studies, a "normal" gene is inserted into the genome to replace an "abnormal," disease-causing gene. A carrier molecule called a vector must be used to deliver the therapeutic gene to the patient's target cells. Currently, the most common vector is a virus that has been genetically altered to carry normal human DNA. Viruses have evolved a way of encapsulating and delivering their genes to human cells in a pathogenic manner. Scientists have tried to take advantage of this capability and manipulate the virus genome to remove disease-causing genes and insert therapeutic genes.

Target cells such as the patient's liver or lung cells are infected with the viral vector. The vector then unloads its genetic material containing the therapeutic human gene into the target cell. The generation of a functional protein product from the therapeutic gene restores the target cell to a normal state. See a diagram depicting this process.
Some of the different types of viruses used as gene therapy vectors:

• Retroviruses - A class of viruses that can create double-stranded DNA copies of their RNA genomes. These copies of its genome can be integrated into the chromosomes of host cells. Human immunodeficiency virus (HIV) is a retrovirus.
• Adenoviruses - A class of viruses with double-stranded DNA genomes that cause respiratory, intestinal, and eye infections in humans. The virus that causes the common cold is an adenovirus.
• Adeno-associated viruses - A class of small, single-stranded DNA viruses that can insert their genetic material at a specific site on chromosome 19.
• Herpes simplex viruses - A class of double-stranded DNA viruses that infect a particular cell type, neurons. Herpes simplex virus type 1 is a common human pathogen that causes cold sores.

Besides virus-mediated gene-delivery systems, there are several nonviral options for gene delivery. The simplest method is the direct introduction of therapeutic DNA into target cells. This approach is limited in its application because it can be used only with certain tissues and requires large amounts of DNA.

Another nonviral approach involves the creation of an artificial lipid sphere with an aqueous core. This liposome, which carries the therapeutic DNA, is capable of passing the DNA through the target cell's membrane.

Therapeutic DNA also can get inside target cells by chemically linking the DNA to a molecule that will bind to special cell receptors. Once bound to these receptors, the therapeutic DNA constructs are engulfed by the cell membrane and passed into the interior of the target cell. This delivery system tends to be less effective than other options.

Researchers also are experimenting with introducing a 47th (artificial human) chromosome into target cells. This chromosome would exist autonomously alongside the standard 46 - not affecting their workings or causing any mutations. It would be a large vector capable of carrying substantial amounts of genetic code, and scientists anticipate that, because of its construction and autonomy, the body's immune systems would not attack it. A problem with this potential method is the difficulty in delivering such a large molecule to the nucleus of a target cell.

What is the current status of gene therapy research?

The Food and Drug Administration (FDA) has not yet approved any human gene therapy product for sale. Current gene therapy is experimental and has not proven very successful in clinical trials. Little progress has been made since the first gene therapy clinical trial began in 1990. In 1999, gene therapy suffered a major setback with the death of 18-year-old Jesse Gelsinger. Jesse was participating in a gene therapy trial for ornithine transcarboxylase deficiency (OTCD). He died from multiple organ failures 4 days after starting the treatment. His death is believed to have been triggered by a severe immune response to the adenovirus carrier.

Another major blow came in January 2003, when the FDA placed a temporary halt on all gene therapy trials using retroviral vectors in blood stem cells. FDA took this action after it learned that a second child treated in a French gene therapy trial had developed a leukemia-like condition. Both this child and another who had developed a similar condition in August 2002 had been successfully treated by gene therapy for X-linked severe combined immunodeficiency disease (X-SCID), also known as "bubble baby syndrome."

FDA's Biological Response Modifiers Advisory Committee (BRMAC) met at the end of February 2003 to discuss possible measures that could allow a number of retroviral gene therapy trials for treatment of life-threatening diseases to proceed with appropriate safeguards. In April of 2003 the FDA eased the ban on gene therapy trials using retroviral vectors in blood stem cells.

What factors have kept gene therapy from becoming an effective treatment for genetic disease?

• Short-lived nature of gene therapy - Before gene therapy can become a permanent cure for any condition, the therapeutic DNA introduced into target cells must remain functional and the cells containing the therapeutic DNA must be long-lived and stable. Problems with integrating therapeutic DNA into the genome and the rapidly dividing nature of many cells prevent gene therapy from achieving any long-term benefits. Patients will have to undergo multiple rounds of gene therapy.
• Immune response - Anytime a foreign object is introduced into human tissues, the immune system is designed to attack the invader. The risk of stimulating the immune system in a way that reduces gene therapy effectiveness is always a potential risk. Furthermore, the immune system's enhanced response to invaders it has seen before makes it difficult for gene therapy to be repeated in patients.
• Problems with viral vectors - Viruses, while the carrier of choice in most gene therapy studies, present a variety of potential problems to the patient --toxicity, immune and inflammatory responses, and gene control and targeting issues. In addition, there is always the fear that the viral vector, once inside the patient, may recover its ability to cause disease.
• Multi-gene disorders - Conditions or disorders that arise from mutations in a single gene are the best candidates for gene therapy. Unfortunately, some the most commonly occurring disorders, such as heart disease, high blood pressure, Alzheimer's disease, arthritis, and diabetes, are caused by the combined effects of variations in many genes. Multi-gene or multi-factorial disorders such as these would be especially difficult to treat effectively using gene therapy. For more information on different types of genetic disease, see Genetic Disease Information.

What are some recent developments in gene therapy research?

• Nanotechnology + gene therapy yields treatment to torpedo cancer. March, 2009. The School of Pharmacy in London is testing a treatment in mice, which delivers genes wrapped in nanoparticles to cancer cells to target and destroy hard-to-reach cancer cells. Read BBC article.
• Results of world's first gene therapy for inherited blindness show sight improvement. 28 April 2008. UK researchers from the UCL Institute of Ophthalmology and Moorfields Eye Hospital NIHR Biomedical Research Centre have announced results from the world's first clinical trial to test a revolutionary gene therapy treatment for a type of inherited blindness.
• A combination of two tumor suppressing genes delivered in lipid-based nanoparticles drastically reduces the number and size of human lung cancer tumors in mice during trials conducted by researchers from The University of Texas M. D. Anderson Cancer Center and the University of Texas Southwestern Medical Center.
• Researchers at the National Cancer Institute (NCI), part of the National Institutes of Health, successfully reengineer immune cells, called lymphocytes, to target and attack cancer cells in patients with advanced metastatic melanoma. This is the first time that gene therapy is used to successfully treat cancer in humans.
• Gene therapy is effectively used to treat two adult patients for a disease affecting nonlymphocytic white blood cells called myeloid cells. Myeloid disorders are common and include a variety of bone marrow failure syndromes, such as acute myeloid leukemia. The study is the first to show that gene therapy can cure diseases of the myeloid system.
• Gene Therapy cures deafness in guinea pigs. Each animal had been deafened by destruction of the hair cells in the cochlea that translate sound vibrations into nerve signals. A gene, called Atoh1, which stimulates the hair cells' growth, was delivered to the cochlea by an adenovirus. The genes triggered re-growth of the hair cells and many of the animals regained up to 80% of their original hearing thresholds. This study, which many pave the way to human trials of the gene, is the first to show that gene therapy can repair deafness in animals.
• University of California, Los Angeles, research team gets genes into the brain using liposomes coated in a polymer call polyethylene glycol (PEG). The transfer of genes into the brain is a significant achievement because viral vectors are too big to get across the "blood-brain barrier." This method has potential for treating Parkinson's disease.
• RNA interference or gene silencing may be a new way to treat Huntington's. Short pieces of double-stranded RNA (short, interfering RNAs or siRNAs) are used by cells to degrade RNA of a particular sequence. If a siRNA is designed to match the RNA copied from a faulty gene, then the abnormal protein product of that gene will not be produced.
• New gene therapy approach repairs errors in messenger RNA derived from defective genes. Technique has potential to treat the blood disorder thalassaemia, cystic fibrosis, and some cancers.
• Gene therapy for treating children with X-SCID (sever combined immunodeficiency) or the "bubble boy" disease is stopped in France when the treatment causes leukemia in one of the patients.
• Researchers at Case Western Reserve University and Copernicus Therapeutics are able to create tiny liposomes 25 nanometers across that can carry therapeutic DNA through pores in the nuclear membrane.
• Sickle cell is successfully treated in mice.

---

COMBINING RESISTANCE AND ENDURANCE TRAINING BEST FOR HEART HEALTH, TRIATHLON STUDY FINDS

A study of triathletes published in the online edition and October issue of Radiology reveals that the heart adapts to triathlon training by working more efficiently.

"To our knowledge, this is the first study using MRI to investigate effects of triathlon training on cardiac adaptations," said lead researcher Michael M. Lell, M.D., associate professor at the University of Erlangen-Nuremberg in Erlangen, Germany.

Dr. Lell and colleagues conducted cardiac MRI on 26 professional male triathletes (mean age 27.9) and 27 male controls (mean age 27.3), who were recreationally active no more than three hours per week. Triathletes in the study were top national and international competitors with six or more years of continuous training.

Triathlons are multi-sport events consisting of swimming, cycling and running various distances in succession.

The cardiac MR images revealed that, compared to the recreational athletes, the triathletes had larger left atria and larger right and left ventricles. The triathletes' left and right ventricles also had greater muscle mass and wall thickness.
"In competitive athletes, it is important to distinguish physiological adaptations as a result of training from pathological conditions such as cardiomyopathy, the most common cause of sudden cardiac death," Dr. Lell said.
In cardiomyopathy, the size of the heart's four chambers and the thickness of the heart wall become asymmetrical, and the heart muscle is unable to pump effectively.

"The cardiac adaptations in the elite triathletes we studied were characterized by a balanced increase in left and right ventricular muscle mass, wall thickness, dilation and diastolic function," Dr. Lell said. "These adaptations reflect the nature of triathlon training, which has both endurance and resistance components."
Dynamic or endurance training includes activities such as running and swimming. Weightlifting is an example of static or resistance training, and cycling is a combination of both forms of exercise. Excessive training in either resistance or endurance disciplines leads to specific heart adaptations, and extreme endurance training is thought to be associated with a predisposition to sudden cardiac events.

"Cardiac adaptations in elite triathletes in our study were not associated with sudden cardiac death," Dr. Lell said.
The triathletes' resting heart rates were also 17 percent lower than those of the control group, which leads to greater cardiac blood supply and more economized heart function.
"The hearts of the triathletes in our study are stronger and able to manage the same workload with less effort," said Dr. Lell.

'NO TIME TO EXERCISE' IS NO EXCUSE

A new study, published in The Journal of Physiology, shows that short bursts of very intense exercise - equivalent to only a few minutes per day - can produce the same results as traditional endurance training.

"The most striking finding from our study was the remarkably similar improvements in muscle health and performance induced by two such diverse training strategies," says Martin Gibala, an associate professor of kinesiology at McMaster University.

Gibala's team made headlines last year when they suggested that a few minutes of high-intensity exercise could be as effective as an hour of moderate activity. However, their previous work did not directly compare sprint versus endurance training.

The new study was conducted on 16 college-aged students who performed six training sessions over two weeks. Eight subjects performed between four and six 30-second bursts of "all out" cycling separated by 4 minutes of recovery during each training session. The other eight subjects performed 90-120 minutes of continuous moderate-intensity cycling each day. Total training time commitment including recovery was 2.5 hours in the sprint group, whereas the endurance group performed 10.5 hours of total exercise over two weeks. Despite the marked difference in training volume, both groups showed similar improvements in exercise performance and muscle parameters associated with fatigue resistance.

"Our study demonstrates that interval-based exercise is a very time-efficient training strategy," said Gibala. "This type of training is very demanding and requires a high level of motivation. However, short bursts of intense exercise may be an effective option for individuals who cite 'lack of time' as a major impediment to fitness."

---

PREVENTING CHILDHOOD OBESITY - GUIDANCE FROM PREVIOUS STUDIES

Extensive analyses to identify best practice in the prevention of childhood obesity have recently been undertaken. 1,2 However, these expert reviews have failed to come up with a specific ‘blueprint' for future interventions. This is not surprising considering the diversity in scope and design of individual studies. Nevertheless a number of key considerations have been highlighted that will help guide future childhood obesity prevention programmes.

Physical activity

To avoid weight reduction for those who are already lean as well as unhealthy slimming practices and to prevent stigmatization of children who are already overweight, any intervention aimed at the general child population must focus on healthy eating, active living and positive self-esteem rather than weight loss or the achievement of ideal body weight. Experts reviews found that including physical activity was an essential component of any intervention for reducing body fatness. The reduction of time spent being sedentary was also thought to show promise. Doak highlighted the success of interventions aimed at reducing the time children spend watching television and recommended this component should be included where children's TV viewing and computer gaming is extensive.

Stakeholder involvement

The reason why no single measure for obesity prevention can be identified is that different approaches are required in different situations. The most successful initiatives are those that adapt the intervention programme to the specific needs of the child (in terms of their age, sex and ethnicity), work creatively taking into consideration the facilities and expertise available and most importantly seek stakeholder's input during programme development, implementation and evaluation. Stakeholders are those directly affected by the intervention programme like children, teachers, parents and community leaders. Their involvement not only helps tailor the programme to their specific needs but also creates a sense of ownership and a will to succeed. Stakeholder's involvement is especially important for programmes targeting minority groups.

Scope and setting

Schools have emerged as a pivotal setting for the promotion of healthy weight as they have access to the majority of the child population. Apart from being an obvious place to educate children on healthy living, schools can provide practical, positive changes in diet and exercise behaviour by offering healthy food in the canteen and creating opportunities for physical activity during lesson time, break-times and after-school clubs. But ideally the school should act as a hub for a more extensive programme involving families and the wider community. The influence of parents and family cannot be underestimated and the education and active involvement of parents should be built into the programme. Similarly public participation is at the heart of a wider community involvement and should be called upon to harness skills, knowledge and resources to act on community identified health issues.

It's the way that you do it!

Flynn highlights that the programme leader and/or facilitator's personal characteristics are likely to have a very important effect on the success of the programme. Apart from good communication and motivational skills, the facilitator must be culturally acceptable and serve as a positive role model. It is recommended that facilitator qualities should be considered during study design and set up of the intervention.

Towards positive change

The vast majority of studies to date have, in the short-term, demonstrated change towards improvement and although concern has been voiced that the promotion of healthy weights amongst children could have negative effects on body image and cause stigmatisation of those already overweight and obese, there is little evidence that this is the case. Flynn also suggest that large scale programmes to tackle childhood obesity could maximize resources by addressing other chronic diseases like heart disease and cancer at the same time as the strategies to prevent them are broadly the same.

References

• Flynn M.A.T. et al (2006). Reducing obesity and related chronic disease risk in children and youth: a syntheses of evidence with best practice recommendations. Obesity Reviews 7 (suppl 1): 7-66
• Doak C.M. et al (2006). The prevention of overweight and obesity in children and adolescents: a review of interventions and programmes. Obesity Reviews 7: 111-136

---

TEENAGE BRAIN: A WORK IN PROGRESS (FACT SHEET)

A brief overview of research into brain development during adolescence

New imaging studies are revealing - for the first time - patterns of brain development that extend into the teenage years. Although scientists don't know yet what accounts for the observed changes, they may parallel a pruning process that occurs early in life that appears to follow the principle of "use-it-or-lose-it:" neural connections, or synapses, that get exercised are retained, while those that don't are lost. At least, this is what studies of animals' developing visual systems suggest. While it's known that both genes and environment play major roles in shaping early brain development, science still has much to learn about the relative influence of experience versus genes on the later maturation of the brain. Animal studies support a role for experience in late development, but no animal species undergoes anything comparable to humans' protracted childhood and adolescence. It is yet not clear whether experience actually creates new neurons and synapses, or merely establishes transitory functional changes. Nonetheless, it's tempting to interpret the new findings as empowering teens to protect and nurture their brain as a work in progress.

The newfound appreciation of the dynamic nature of the teen brain is emerging from MRI (Magnetic Resonance Imaging) studies that scan a child's brain every two years, as he or she grows up. Individual brains differ enough that only broad generalizations can be made from comparisons of different individuals at different ages. But following the same brains as they mature allows scientists a much finer-grained view into developmental changes. In the first such longitudinal study of 145 children and adolescents, reported in l999, NIMH's Dr. Judith Rapoport and colleagues were surprised to discover a second wave of overproduction of gray matter, the thinking part of the brain - neurons and their branch-like extensions - just prior to puberty. Possibly related to the influence of surging sex hormones, this thickening peaks at around age 11 in girls, 12 in boys, after which the gray matter actually thins some.

Prior to this study, research had shown that the brain overproduced gray matter for a brief period in early development - in the womb and for about the first 18 months of life - and then underwent just one bout of pruning. Researchers are now confronted with structural changes that occur much later in adolescence. The teen's gray matter waxes and wanes in different functional brain areas at different times in development. For example, the gray matter growth spurt just prior to puberty predominates in the frontal lobe, the seat of "executive functions" - planning, impulse control and reasoning. In teens affected by a rare, childhood onset form of schizophrenia that impairs these functions, the MRI scans revealed four times as much gray matter loss in the frontal lobe as normally occurs.

Unlike gray matter, the brain's white matter - wire-like fibers that establish neurons' long-distance connections between brain regions - thickens progressively from birth in humans. A layer of insulation called myelin progressively envelops these nerve fibers, making them more efficient, just like insulation on electric wires improves their conductivity.

Advancements in MRI image analysis are providing new insights into how the brain develops. UCLA's Dr. Arthur Toga and colleagues turned the NIMH team's MRI scan data into 4-D time-lapse animations of children's brains morphing as they grow up - the 4th dimension being rate-of-change. Researchers report a wave of white matter growth that begins at the front of the brain in early childhood, moves rearward, and then subsides after puberty. Striking growth spurts can be seen from ages 6 to 13 in areas connecting brain regions specialized for language and understanding spatial relations, the temporal and parietal lobes. This growth drops off sharply after age 12, coinciding with the end of a critical period for learning languages.

While this work suggests a wave of brain white matter development that flows from front to back, animal, functional brain imaging and postmortem studies have suggested that gray matter maturation flows in the opposite direction, with the frontal lobes not fully maturing until young adulthood. To confirm this in living humans, the UCLA researchers compared MRI scans of young adults, 23-30, with those of teens, 12-16. They looked for signs of myelin, which would imply more mature, efficient connections, within gray matter. As expected, areas of the frontal lobe showed the largest differences between young adults and teens. This increased myelination in the adult frontal cortex likely relates to the maturation of cognitive processing and other "executive" functions. Parietal and temporal areas mediating spatial, sensory, auditory and language functions appeared largely mature in the teen brain. The observed late maturation of the frontal lobe conspicuously coincides with the typical age-of-onset of schizophrenia - late teens, early twenties - which, as noted earlier, is characterized by impaired "executive" functioning.

Another series of MRI studies is shedding light on how teens may process emotions differently than adults. Using functional MRI (fMRI), a team led by Dr. Deborah Yurgelun-Todd at Harvard's McLean Hospital scanned subjects' brain activity while they identified emotions on pictures of faces displayed on a computer screen. Young teens, who characteristically perform poorly on the task, activated the amygdala, a brain center that mediates fear and other "gut" reactions, more than the frontal lobe. As teens grow older, their brain activity during this task tends to shift to the frontal lobe, leading to more reasoned perceptions and improved performance. Similarly, the researchers saw a shift in activation from the temporal lobe to the frontal lobe during a language skills task, as teens got older. These functional changes paralleled structural changes in temporal lobe white matter.

While these studies have shown remarkable changes that occur in the brain during the teen years, they also demonstrate what every parent can confirm: the teenage brain is a very complicated and dynamic arena, one that is not easily understood.

References

1. Giedd JN, Blumenthal J, Jeffries NO, et al. Brain development during childhood and adolescence: a longitudinal MRI study. Nature Neuroscience, 1999; 2(10): 861-3.
2. Rapoport JL, Giedd JN, Blumenthal J, et al. Progressive cortical change during adolescence in childhood-onset schizophrenia. A longitudinal magnetic resonance imaging study. Archives of General Psychiatry, 1999; 56(7): 649-54.
3. Thompson PM, Giedd JN, Woods RP, et al. Growth patterns in the developing brain detected by using continuum mechanical tensor maps. ;Nature, 2000; 404(6774): 190-3.
4. Sowell ER, Thompson PM, Holmes CJ, et al. In vivo evidence for post-adolescent brain maturation in frontal and striatal regions.Nature Neuroscience, 1999; 2(10): 859-61.
5. Baird AA, Gruber SA, Fein DA, et al. Functional magnetic resonance imaging of facial affect recognition in children and adolescents.Journal of the American Academy of Child and Adolescent Psychiatry, 1999; 38(2): 195-9.