Hereditary Motor and Sensory Neuropathy with Agenesis of the Corpus Callosum (HMSN/ACC) is a progressive hereditary neuromuscular disorder that mainly affects people from the Saguenay-Lac-St-Jean (SLSJ) and Charlevoix regions of Quebec as well as people whose ancestors originated from these regions. Some cases of HMSN/ACC have also been identified in other countries.
HMSN/ACC is responsible for the degeneration of the peripheral nerves involved in both body movement and the perception of sensations. Irregularities are observed in the brain of people affected with HMSN/ACC, mainly in the anatomical structure connecting the two cerebral hemispheres known as the corpus callosum. The corpus callosum is completely absent in 57.8% of patients and partially absent in 9.4% of patients. The presence or absence of corpus callosum in the brain of people affected does not seem to influence the severity or nature of symptoms.
Men and women are equally affected. There are approximately one hundred people living with HMSN/ACC in Quebec.
HMSN/ACC is an autosomal recessive genetic disorder. It is caused by a gene mutation located on chromosome 15, one of the 22 autosomal pairs of chromosomes. The gene is expressed (resulting in the manifestation of HMSN/ACC) only when it is inherited from both parents. This means that both parents must be carriers of the gene. Often, carriers of the HMSN/ACC gene do not have symptoms and do not know that they are carriers.
When both parents are carriers of the HMSN/ACC gene, at each pregnancy:
The carrier status of the HMSN/ACC gene can be confirmed through genetic testing. If you have a family history of HMSN/ACC, you may wish to consult a genetic counselor to understand your chances of having a child affected with HMSN/ACC and discuss family planning alternatives.
A paediatrician and/or neurologist will conduct a clinical examination, as well as genetic testing to confirm diagnosis of HMSN/ACC. Additional testing may be recommended, such as a brain scan performed with highly precise radiography technology (cerebral tomography) or an analysis of the electrical activity in the arm and leg muscles (electromyogram).
Symptoms appear shortly after birth or during the first year of life and are characterized by a lack of muscle strength and a delay in the development of motor skills. HMSN/ACC results in a loss of mobility and developmental abnormalities in the spine, hands, and feet. In addition to the physical symptoms, HMSN/ACC also causes mild to moderate cognitive impairment.
Babies with HMSN/ACC have difficulty sitting and crawling. An intensive physiotherapy and occupational therapy treatment can stimulate motor development. With the use of assistive devices, such as feet and ankle orthoses, walkers, quadripods or support canes, toddlers usually begin to walk around the age of two or three. Typically, a child affected with HMSN/ACC has a slow gait and poor balance. In most cases, tremors are experienced throughout all parts of the body.
Children with HMSN/ACC experience delays in gross and fine motor development. Young children will be less prone to use their arms. Handgrip strength is weak, and keeping a grip on an object often requires extra exertion. Sometimes, this weakness in the upper limbs will cause muscle tremors when under strain. Often, children with HMSN/ACC are hypersensitive to touch. They are rarely toilet trained before the age of three.
Language development is delayed and learning capacity is affected. Students with HMSN/ACC usually require the support of a teaching assistant, or may be placed in a specialized class. Most children with HMSN/ACC learn to read, write, and count and are able to acquire general knowledge. However, skills typically remain at a second grade level.
Children with HMSN/ACC are usually very sociable, affectionate, and cheerful, and are able to integrate well in school and group activities. Additionally, they are able to follow codes of conduct and demonstrate social and moral judgment.
Around the age of twelve, the orthopedic surgeon may recommend scoliosis surgery to correct the curvature or bending of the spine. This surgery allows for a better expansion of the lungs and other organs as well as a better body alignment. Prior to the surgery, some children wear a corset for a few years to minimize the curvature of the spine or delay of the surgery. However, the corset is not a substitute for the surgery.
With the help of a walker, some people with HMSN/ACC will be able to walk until their early twenties. Many teenagers, however, will use a manual wheelchair or an electric scooter for mobility.
By the end of the teenage years or at the beginning of adulthood, some people may experience episodes of anxiety, agitation, visual or auditory hallucinations or depression. These problems are caused by dysfunctions in the brain and may require treatment.
Due to the progressive nature of the disorder, the person affected typically requires a power wheelchair and assistance with their personal needs by early twenties. Respiratory muscle weakness results in a high risk of respiratory failure and bronchopneumonia, which can be fatal. The average life span is 29 years, although many have lived up to their forties.
Currently, there is no known cure for HMSN/ACC or treatments to prevent the onset of symptoms. However, therapeutic interventions offered by various health care providers may help maintain physical abilities, avoid further complications and enhance comfort.
A physiotherapist assesses motor development, joint mobility, and muscle strength. Regular therapy during the preschool period helps in the development of motor skills (i.e. sitting, crawling, standing, walking), posture, and range of motion. As the child grows, a physiotherapist continues to monitor and assess functional independence, mobility, and muscle strength, and recommends technical aids to meet the individual’s changing needs.
Occupational therapy helps foster motor development and skills. Play and activities related to daily living are used to improve awareness of the environment and enhance manual dexterity. An occupational therapist plays an essential role during both the child’s integration into school and the schooling period. This may include recommending a wide range of specialized equipment and modifications to the daycare, home, and/or school environment.
A neurologist ensures the life-long monitoring of the disorder, and can answer questions regarding the evolution of the disorder. A neurologist may prescribe medications if problems arise during the course of the disorder.
A pneumologist and/or respirologist assesses the respiratory condition and prescribes appropriate treatments, including drugs, breathing exercises, and mechanical ventilation support.
Learning that a child is diagnosed with HMSN/ACC is often an emotional shock for parents. Rehabilitation professionals help parents familiarize themselves with exercises and programs to foster their child’s development. Parental involvement, support, and care are crucial in the rehabilitation process.
It is suggested that parents look for babysitting or child care services or make arrangements for occasional breaks for care-giving. Having supplemental child care helps the child develop his/her social skills and enhance his/her maturity. These arrangements are also greatly beneficial to parents.
Many people with HMSN/ACC live a fulfilling life expressing their needs and feelings and surrounded by the love and affectionate care of their family. It is important to encourage people with HMSN/ACC to develop social contacts and connections (i.e. through school or recreational activities).
A person living with HMSN/ACC experiences challenging phases that have major impacts on their family. Each person and family copes and adapts differently; support is available through community and professional services.
The gene responsible for HMSN/ACC was localized in 1996 and identified in 2002 by scientists from Quebec. More than 99% of persons affected show a common single alteration in this gene. This mutation can be detected through genetic analysis of a blood sample. Research is being pursued to better understand the protein produced by this gene and its function.
Carrefour de la Santé de Jonquière 2230 rue de l’Hôpital, C.P. 15
Jonquière, Qc G7X 7X2
Centre Hospitalier de Charlevoix
74, rue Ambroise- Fafard Baie
Saint-Paul, QC G3Z 2J6
(418) 435-5150, ext. 2086 and 2087
Complexe Hospitalier de la Sagamie 305, St- Vallier C.P. 67
Chicoutimi, QC G7H 5H6
(418) 541-1234, ext. 2153 or 2081
1425, boul. René-Lévesque Ouest, bureau 506
Toll Free: 1-800-567-2873
Acknowledgements: Muscular Dystrophy Canada would like to recognize and thank Dr. Jean Mathieu and Ms. Claude Prévost for their valuable assistance preparing and reviewing this information.
Updated May 2013.