Canavan disease

Carriers of autosomal recessive conditions such as Canavan disease generally do not show symptoms of the condition and are often unaware that they carry a change in the gene responsible. Family members of those with Canavan disease may wish to know whether they are carriers of a change in the ASPA gene for family planning purposes. Anyone who is a blood relative of a person with Canavan syndrome can be tested to see whether they are a carrier. It is best if the genetic changes in the ASPA gene that cause Canavan syndrome in the family are known before carrier testing of more distant relatives is done. A genetic counselor or physician with experience in Canavan disease can provide advice about how a diagnosis of the disorder can impact other family members.

Popular social media sites including Facebook can be great resources for connecting with other families with children who have Canavan disease. The following support groups may also have events where you can meet other families who are affected by Canavan disease: The [link url="www.canavanfoundation.org” target=”_blank”>Canavan Foundation and the National Tay-Sachs and Allied Diseases Association (NTSAD).

There are also online communities for rare disorders such as RareConnect, RareShare, or Inspire, which allow individuals and parents to share experiences and advice about dealing with rare disorders.

The medical costs of Canavan disease can be significant. Some families lack the resources necessary to provide for a chronically or terminally ill child. There are several organizations that provide financial assistance for Canavan families.

The Social Security Administration has a Compassionate Allowances Initiative. This program speeds up the processing of disability claims for people with specific medical conditions that cause severe disability. Canavan disease is included on this list. The Canavan Foundation and the Disability Benefits Center have information on compassionate Allowance for Canavan disease.

The National Organization for Rare Disorders has links to organizations that can provide financial assistance.

The National Human Genome Research Institute has extensive information on finding financial aid for medical treatment and services.

Rare diseases like Canavan disease that affect multiple organ systems can benefit from a multidisciplinary approach. This approach involves healthcare professionals with specialized skills and expertise. They work together to make treatment recommendations and to provide quality care of individuals and families. Depending upon the specific symptoms in an individual with Canavan disease, a multidisciplinary team may require a specialist for neurological disorders in children (pediatric neurologist) who will monitor brain function and health; an eye doctor (ophthalmologist) who can periodically check for optic atrophy and vision loss; a specialist in digestive disorders (gastroenterologist); a psychiatrist to monitor and treat emotional problems; a genetic counselor who can help people understand the disease and the implications for the family, a metabolic disease specialist, physiotherapists, physical therapists, occupational therapists, and nutritionists.

A few different therapies are being explored as potential treatments for Canavan disease. These include gene therapy, stem cell therapy, enzyme replacement therapy, lithium citrate, and acetate replacement. Gene therapy replaces the defective gene in a person with an unaffected one that can produce the necessary aspartoacylase enzyme. Gene therapy trials began in 2000. These studies have shown some positive results including the improvement of certain symptoms and decreased levels of N-acetylaspartic acid (NAA) in the brain. As of 2019, gene therapy has not been approved by the U.S. Food and Drug Administration for the treatment of any disorder.

Stem cell therapy involves taking adult stem cells and altering them to become cells that can help repair the myelin sheath that is damaged in people with Canavan disease. The myelin sheath coats, protects, and insulates nerve fibers. Researchers hope that repairing this damage can help stop or slow the progression of neurological damage in Canavan disease.

Enzyme replacement therapy replaces the aspartoacylase enzyme with a synthetic version engineered in a laboratory. This synthetic form is engineered to be able to enter the brain and is injected into the bloodstream where it travels to the brain. Lithium citrate is a chemical compound that can reduce the levels of NAA in the brain. Researchers believe that lithium citrate can reduce elevated levels of NAA in the brain in children with Canavan disease and possibly slow or stop the progression of the disease. The enzyme defect in Canavan disease leads to a lack of a substance called acetate in the brain. Some researchers are studying whether replacing acetate in the brain can help children with Canavan disease.

Children with Canavan disease may need lots of different medical equipment. Parents may need to get a pediatric wheelchair, strollers, feeding pump and supplies, adaptive chairs, and bath chairs to name just a few. These devices can be expensive. Low muscle tone called hypotonia can be persistent in Canavan disease. Parents may need to get foam supports, feeder seats, and specialized strollers. Children who have problems breathing may need oxygen tanks and concentrators. Certain support groups and nonprofits provide information on medical equipment. A doctor or other medical specialist can work with families to get or advocate for medical equipment.

The common abbreviation for Canavan disease is CD.

Canavan disease can be very different in one child as opposed to another. It is difficult to make predictions about how the disease will progress for an individual child. Most people with the infantile form live only into childhood, although some survive into adolescence or beyond. People with the milder form of the condition do not appear to have a shortened lifespan.

Canavan disease occurs with greater frequency in people of Eastern European (Ashkenazi) Jewish descent. If both parents have a nonfunctioning copy of ASPA gene, there is a 25% for each pregnancy that a child with have Canavan disease. Doctors strongly recommend that people of Ashkenazi Jewish heritage undergo carrier screening for Canavan disease. This involves a simple blood test to detect one of the two alterations in the ASPS gene that cause Canavan disease in this particular population.

Carrier screening is usually done through a doctor’s office or a hospital-based medical genetics program. The results generally take about 2 weeks. However, advances in technology are making such testing more accessible to families. JScreen is a program managed by the Emory School of Medicine’s Department of Human Genetics, provides at-home genetic screening and private counseling for Jewish people to determine their risk.

Carrier screening is most effective before beginning to start a family. Family planning is an important step for people at risk for having a child with a genetic disorder. A consultation with a genetic counselor is important to learn potential risk to the child and reproductive options for the couple. Support groups like the Canavan Foundation provide information on options for carrier couples.

Canavan disease is a rare genetic condition that damages the ability of nerve cells (neurons) in the brain to send and receive messages. People with this disorder lack an enzyme that is essential for the growth and maintenance of myelin. Myelin is a covering or "sheath" that coats, protects, and insulates nerve fibers. Collectively, myelin-covered nerve fibers are known as the white matter. Canavan disease can be separated into a severe infantile form and a milder juvenile form.

The infantile Canavan disease is the most common and most severe form of the condition. Affected infants appear normal for the first few months of life, but by age 3 to 5 months, problems with development become noticeable. These infants usually do not develop motor skills such as turning over, controlling head movement, and sitting without support. Other common features of this condition include weak muscle tone (hypotonia), an unusually large head size (macrocephaly), and irritability. Feeding and swallowing difficulties, seizures, and sleep disturbances may also develop. The juvenile form of Canavan disease is less common. Affected individuals have mildly delayed development of speech and motor skills starting in childhood. These delays may be so mild and nonspecific that they are never recognized as being caused by Canavan disease.

The life expectancy for people with Canavan disease varies. Most people with the neonatal/infantile form live only into childhood, although some survive into adolescence or beyond. People with the mild/juvenile form do not appear to have a shortened lifespan.

Children with the infantile form of Canavan disease can have problems in their development that become noticeable around 3-5 months. They show delays in reaching developmental milestones such as rolling over, holding their head up, or sitting up without assistance. As they age, there can be delays in crawling, walking and talking. Children may experience seizures, vision loss, and sleep disturbances. People with the milder form of Canavan disease may have speech and learning problems in childhood.

Canavan disease is caused by unexpected changes in the ASPA gene. This gene is responsible for making an enzyme called aspartoacylase. Aspartoacylase breaks down a compound mostly found in the brain called N-acetyl-L-aspartic acid (NAA). Changes in the ASPA gene make aspartoacylase less able to break down NAA, causing the compound to build up in the brain, specifically brain cells (neurons). When enzyme activity is reduced or absent (ineffective), NAA builds up in nerves cells and those cells and the surrounding nerve tissue are damaged. NAA is believed to be essential to the health and formation of myelin. Myelin is a covering or "sheath" that coats, protects, and insulates nerve fibers. When myelin breaks down, a process called demyelination, the nerves cannot function well. The brain uses nerves to tells the body what to do. Demyelination means the brain can’t communicate effectively to other areas of the body. This results in progressive neurological deterioration.

Unexpected changes in the ASPA gene have been shown to cause Canavan disease. This is the only gene in which unexpected changes are known to cause the disease. Genes are segments of DNA found on chromosomes. Genes produce specific proteins that the body needs to grow and work properly. When there is an unexpected change in a gene, the protein that the gene produces may be absent, deficient, or faulty and ineffective. The ASPA gene gives instructions to the body to make an enzyme called aspartoacylase.

Having a “variant” in the genes responsible for Canavan disease (ASPA) means that a change was detected in the gene but there is currently not enough research or evidence to say whether it can cause Canavan disease or not. For example, it may be the first time a specific change in the gene has been identified. It may be termed a "variant of unknown significance." As more research is performed, the “variant” may be classified as disease causing (pathogenic) or not disease causing (benign).

Canavan disease demands a lot of time and focus from parents. As with similar disorders, it is easy for healthy siblings to feel as if they have been pushed aside. Although studies have shown that siblings of children with chronic illness tend to develop strong levels of compassion and empathy, these studies have also shown that siblings can develop feelings of jealousy and anger and high levels of anxiety. Parents can work with siblings by having clearly defined roles and responsibilities within the family structure. Siblings can help with the care of their sick sibling. Parents are encouraged to make time for activities especially for healthy siblings and to talk with and encourage healthy siblings to address their concerns and feelings. Some children may benefit from support outside of the immediate family including therapists or doctors. The Sibling Support Project is a nonprofit organization that serves the concerns and needs of siblings of people with special health, developmental, and mental health needs.

The infantile form is the most common and most severe form of Canavan disease. Symptoms can be very different from one person to another. Symptoms often become apparent between 3 and 6 months of age. Affected infants often have trouble with rolling over, holding their head up, or sitting up without assistance. Other symptoms may include having a large head (macrocephaly), having low muscle tone (hypotonia), being irritable, and delays in learning to interact socially, smile, or laugh. As affected infants age, low muscle tone may change to increased muscle tone leading to muscle stiffness and difficulties with movement. Affected infants may have damage to the optic nerve (optic atrophy). The optic nerve transmits nerve impulses from the eye to the brain where they are changed to images. Damage to the optic nerve results in progressive loss of vision. Children with Canavan disease may have feeding difficulties, gastroesophageal reflux, seizures, and problems sleeping. They may have problems with swallowing. Some children will never walk or talk. Despite these issues children learn to interact socially, laugh, smile, and reach for objects.

People who have the mild/juvenile form of Canavan disease may not meet developmental milestones in speech and movement as quickly as other children their age. Some of these children may benefit from tutoring and speech therapy. However, the symptoms may be so mild that they are never diagnosed with Canavan disease.

After a diagnosis of Canavan disease is confirmed, families should seek a medical consultation with a physician such as a metabolic genetic specialist with experience in the disorder. Supports groups such as the the Canavan Foundation, the Canavan Research Foundation, and the Canavan Research Illinois. The United Leukodystrophy Foundation, and the National Tay-Sachs and Allied Diseases Association can sometimes provide referrals to physicians or medical centers with experience in treating Canavan disease.

People diagnosed with Canavan disease will go through a series of tests to see how far along the disease is. These tests will tell a physician what parts of the body are affected and to what extent. Other initial steps will depend on how the disorder is affecting a person. Families should see a genetic counselor to help understand the genetic aspects of this disorder.

Canavan disease is not available on newborn screening as of March 2016. However, if there is a family history of Canavan disease or a doctor has reason to suspect a child may have Canavan disease, testing can be done on babies at or shortly after birth.

Several different tests may be used to diagnose Canavan disease. The disorder is caused by gene changes in the ASPA gene. Molecular genetic testing can be used to study the ASPA gene to identify variations or changes in the gene that lead to Canavan disease. Changes in this gene can be found by looking at specific spots within the gene where changes causing Canavan disease are known to occur, looking at the entire gene to look for changes, or looking to see whether areas of the gene have been deleted (missing) or duplicated (extra). Infantile Canavan disease can also be diagnosed by taking a urine sample from the child or amniotic fluid during pregnancy to look at the levels of N-acetyl-L-aspartic acid (NAA) that build up in those with Canavan disease. Very high concentration of NAA indicates a diagnosis of Canavan disease. This build up of NAA in the urine doesn’t occur in the mild/juvenile form, which requires molecular genetic testing to confirm a diagnosis.

People with Canavan disease may undergo additional tests to see how far along the disease is. Magnetic resonance imaging, or an MRI, is a specialized imaging techniques that allow doctors to view structures in the body. Doctors use this test in people with Canavan disease because they can reveal changes in the white matter of the brain. Children with Canavan disease may undergo a developmental and nutritional assessment. A developmental assessment evaluates how a child’s physical, language, emotional, social and intellectual skills are developing. A nutritional assessment evaluates whether a child’s nutritional needs are being met.

The website clinicaltrials.gov is a U.S. government website that provides regularly updated information about federally and privately supported clinical trials. This is not an exhaustive list of current research.Current studies can found by searching for ‘Canavan disease’ on ClinicalTrials.gov.

In Europe, the EU Clinical Trial Register performs a similar service.
To learn about clinical trials sponsored by private sources, you can contact www.centerwatch.com

In addition to the clinical research studies, there is ongoing research into gene therapy, enzyme replacement therapy and stem cell therapy. Gene therapy seeks to replace the defective gene in a person with an unaffected one that can produce the necessary aspartoacylase enzyme. Enzyme replacement therapy replaces the aspartoacylase enzyme that is deficient in Canavan disease with an artificial version that is created in a lab and injected into a person with this disorder. As of 2019, gene therapy has not been approved by the U.S. Food and Drug Administration for the treatment of any disorder. Enzyme replacement therapy has been approved by the FDA for the treatment of disorders that are similar to Canavan disease.

While there is no cure for Canavan disease, the treatment is supportive and aimed at making sure the child gets enough nutrition and stays hydrated. A feeding tube may help make sure a child gets enough food, water, and nutrition and help prevent food or water from getting in the lungs. It is also important to prevent sickness as much as possible and protect the airway. Physical therapy will help children move as best as they can and special education classes can help a child gain or maintain skills. If seizures develop, medication can be given to help treat them. Research is ongoing to find more effective treatment options and potentially a cure for Canavan disease.

Some children with the severe form of Canavan disease may need palliative care. Palliative care ensures that a dying child is as pain free as possible and that all of their physical, social, emotional and spiritual needs are met. Palliative care requires a close cooperation among family members, immediate relatives, and physicians and other medical personnel. A primary care physician or local hospital may be able to offer advice and local resources for palliative care.

The National Tay-Sachs and Allied Diseases Association has information on palliative and hospice that is specific to Canavan disease and related diseases. They stress that the focus is on improving the quality of life for the child and the family.

The International Children’s Palliative Care Network has specific information and support for families considering palliative care for their children.

Canavan disease is classified as a leukodystrophy. Leukodystrophy is a general term for a disorder that affects the growth and health of myelin. Myelin is a covering or "sheath" that coats, protects, and insulates nerve fibers. Collectively, myelin-covered nerve fibers are known as white matter. When myelin breaks down, a process called demyelination, the nerves cannot function well. The brain uses nerves to tells the body what to do. Demyelination means the brain can’t communicate to other areas of the body. This results in progressive neurological deterioration. Broad treatment studies or new therapies that target leukodystrophies as a whole could possibly have applications for people with Canavan disease.

Carriers of an ASPS gene with alterations that causes Canavan disease do not develop symptoms of the disorder. They are at risk of passing Canavan disease on to their children.

One in four, or 25% chance. Canavan disease is inherited in an autosomal recessive pattern, meaning that both parents of a child with the disorder likely carry a change in the ASPA gene. The parents have one working copy of the gene and one nonworking copy; they are carriers for Canavan disease. Both parents must pass along a nonworking copy of the gene. For each individual pregnancy, there is a 25% chance that both parents will pass along a nonworking copy of the gene and the child will have the disorder. There is a 50% chance that one parent will pass on the gene change and the other won’t, meaning the child will be a carrier for the disorder. There is a 25% chance that both parents will pass along a working copy of the gene and the child will not have the disorder and will not be a carrier.

Generally new symptoms to do not appear in later childhood but respiratory health and seizure management become more complicated and challenging. Children with Canavan can live to be teenagers and young adults. Puberty may change symptoms and how they are managed. Girls sometimes experience premature puberty. Talk to your doctor about medications to delay puberty or use of birth control pills to reduce frequency of menstrual cycles.

Canavan disease is inherited in an autosomal recessive manner. We all have two copies of most of our genes. We get one copy from our mother and another copy from our father. In Canavan disease, a person inherits two copies of the ASPA gene that is not working correctly. This causes the disorder. The parents have one working copy of the gene and one nonworking copy; they are carriers for Canavan disease. Carriers do not show symptoms of the condition themselves. Each time two carriers have a child, there is a 25% chance they will have a child with Canavan disease. There is a 50% chance they will have a child who is a carrier, but does not have Canavan disease. There is a 25% chance they will have a child who neither has Canavan disease nor is a carrier for the disorder.

Caregivers of children with chronic illnesses need to take time for themselves and find coping strategies that work for them. Sometimes finding support from other families or parents facing the same challenges can be helpful. The National Tay Sachs and Allied Diseases Association provide coping advice and connects families and parents together. Parent to Parent USA is an organization Emotional & Informational support for families of children who have special needs.

There are lots of ways that parents can cope and find support. Some people find support through keeping a journal, meditation, exercise or talking about the challenges with close friends for professionals.

Support groups have information about supporting research in Canavan disease and most accept donations toward research. Some groups focus specifically on supporting research. Support groups for Canavan disease include the Canavan Foundation, the Canavan Research Foundation, the Canavan Research Illinois, the National Tay Sachs and Allied Diseases Association, and the United Leukodystrophy Foundation.

Testing for Canavan disease is typically ordered by a geneticist and genetic counselor after seeing them for an appointment. A clinic appointment typically involves a complete review of the patient’s medical history, a three generation family history that documents health problems and genetic conditions, a detailed physical examination, discussion of recommended testing, and consent for testing if the patient/guardian is interested. Sometimes this happens in one clinic visit, and sometimes this happens over the span of a few clinic visits. Each clinic is different. In terms of insurance, sometimes the clinic checks with your insurance, and sometimes it is your responsibility to call your insurance. As stated earlier, each clinic operates differently. If testing is pursued, a blood sample and signed paperwork is sent to a laboratory that performs the testing. Results are then sent back to the geneticist and genetic counselor who contact the patient/guardian with results.

To learn about ongoing clinical research into Canavan disease, ask a physician who specializes in the disorder. Genetic counselors and medical geneticists are also excellence sources of information about ongoing clinical trials and can offer advice about the pros and cons about participating in such a trial.

Ongoing studies for Canavan disease can also be found on clinicaltrials.gov, a service of the U.S. National Institutes of Health. In Europe, the EU Clinical Trial Register performs a similar service.

Support groups also have information about research into Canavan disease and ongoing clinical trials as well as information and advice about participating in clinical trials. Support groups for Canavan disease include,

While the symptoms of Canavan disease can vary, most children do not learn to walk or talk. Children may need special accommodations in school. They are eligible for an individual education plan (IEP) or a 504 plan. An IEP is a document that helps to guide the education of a child with a disability or special needs. The plan is individualized for each student. A 504 plan ensures that students with disabilities can fully participate in school and have access to the same educational opportunities as all children. Parents are encouraged to provide a school with a packet of information on Canavan disease and to work with school officials including teachers, nurses, psychologists, the principal, and other professionals.

The U.S. Department of Education has information on individual education plans and on 504 plans.

As with many rare disorders, the incidence and prevalence of Canavan disease is not known. The disorder can affect people of any ethnicity, but occurs in people of Eastern European (Ashkenazi) Jewish heritage more frequently, where it is estimated to occur in about 1 in 6,400 to 1 in 13,500 people. The carrier rate in this population is about 1 in 40-82 people. Canavan disease is believed to be far less common in people of other ancestries. In people of other ancestries, it is estimated to affect about 1 in 100,000 people.

As of May 2016, there are no medications or other known environmental factors that make Canavan disease worse. In caring for children with the neonatal/infantile form, it is important that children with Canavan disease be moved often to help prevent the muscles from becoming stiff and rigid. Also, care should be taken when feeding a child with Canavan disease to avoid food getting into the lungs.

Unexpected changes in the ASPA gene cause Canavan disease. Doctors are not aware of any other factors required for the development of the disorder.

Some parents may choose to have their children tested for Canavan disease before they are born. This is known as prenatal diagnosis. If the gene change that causes Canavan disease is known in a family, then molecular genetic testing (which can detect these changes) can be used for prenatal diagnosis. A sample of tissue can be taken from the placenta and studied. This test is called chorionic villus sampling. Another test is called amniocentesis, which involves taking a sample of the amniotic fluid that surrounds and protects a developing fetus. Cells known as amniocytes are taken from the fluid and studied.

If the gene change is not known, Canavan disease can still be diagnosed before birth through biochemical testing. For this, doctors test the amniotic fluid to determine the levels of N-acetyl-L-aspartic acid (NAA), which will be high in Canavan disease.

Supportive therapies can be used to treat specific symptoms of Canavan disease. Children may benefit from physical therapy to maintain their muscles and special education classes and speech therapy to help with their language and communication. If the child has seizures, they may be treated with anti-seizure medications. Medications can also be used to treat muscle stiffness. A feeding tube (G-tube) may be needed to help the child get enough food and liquids if they have problems with eating or swallowing.

Canavan disease is known by several other names including,

Children with the infantile form of Canavan disease usually do not develop the ability to talk. They may also develop vision loss. Although rare, hearing loss has also been reported.

Children with the milder form of Canavan disease may have some problems with speech and may have learning difficulties.

There are support groups for Canavan disease including the Canavan Foundation, the Canavan Research Foundation, and the Canavan Research Illinois. The United Leukodystrophy Foundation, the National Tay-Sachs and Allied Diseases Association, and the Jewish Genetic Diseases Consortium also provide information and support for families affected by Canavan disease.

Canavan Disease Research (CDR), an international divsion of Canavan Research Illinois, maintains a patient registry called the Canavan patient insight network (PIN). The PIN helps unite Canavan families throughout the world, and enables CDR to better understand the true incidence and prevalence of Canavan disease worldwide.

Infants with Canavan disease show symptoms within the early stages of life. The first few years of a child’s life are critically important to a child’s development. States have federally-funded early intervention programs that support families that have concerns or issues with their children’s development up to the age of three. Some states will continue to offer early intervention programs beyond the age of three. Other states will transition a child into school-based programs that can be provided at home. In some states, a child may be eligible for early intervention services at no charge. Other states may charge a fee, depending on the agencies involved.

The most common form of Canavan disease is the neonatal/infantile form. Infants begin to show symptoms between the first 3-5 months of life. Until that point, the child may appear to be normal. By 3-5 months, the child will not be meeting motor milestones, may have a large head (macrocephaly) and will not have control of their head because of weakened neck muscles (head lag).

A second form of Canavan disease is less common and is called the mild/juvenile form. People with this form of Canavan disease may experience problems with speech or movement starting in childhood. However, the problems may be so mild that they are never diagnosed as being caused by Canavan disease. An infant’s head may be slightly enlarged, but the typical changes in the white matter of the brain (as seen on imaging tests) are absent.

Children with Canavan disease may have persistently weak muscle tone (hypotonia), poor head control or head lag, and a large head (macrocephaly). These symptoms are not unique to Canavan disease, but is associated with the disorder.

There are several other genetic conditions that can cause a loss of nerve cells (neurons) during the infancy period and cause a larger than average head size. Conditions that have similar symptoms are Alexander disease, Tay-Sachs disease, metachromatic leukodystrophy, and glutaricacidemia type 1.

The mild/juvenile form of Canavan disease may be misdiagnosed as a mitochondrial disorder such as Leigh syndrome or metabolic disorders such as glycine encephalopathy.

While there are no centers of excellence for Canavan disease as of March 2016, Paola Leone, Ph.D. of Rowan University’s School of Osteopathic Medicine, is one of the world’s leading researcher in gene therapy for the condition. Guangping Gao, PhD, Professor at the University of Massachusetts Medical School is also studying gene therapy for Canavan disease. Reuben Matalon, MD, PhD in the Departments of Pediatrics and Biochemistry and Molecular Biology at the University of Texas Medical Branch studies Canavan disease. He discovered the defect and cloned the gene for Canavan Disease.

One of the best ways to find a treatment center or physician with experience in treating Canavan disease is to contact a national support group. Support groups for Canavan disease include the Canavan Foundation, the Canavan Research Foundation, the Canavan Disease Research and the United Leukodystrophy Foundation. The National Tay-Sachs and Allied Diseases Association also provides updates and information on research into Canavan disease.

Various complimentary treatment options have been explored for children with Canavan disease. Complementary medicine are treatment methods that can be used along with standard medical practices. Complimentary medicine includes massage therapy, acupuncture and acupressure, music therapy, water (aquatic) therapy, and hippotherapy. Hippotherapy involves using horses to help enhance neurological and physical functioning. Hippotherapy uses the movement of the horse to improve a child’s balance, trunk strength and control and other abilities.