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About ALS and Motor Neuron Disease
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Motor Neuron Diseases (MND) are a group of neurological disorders that affect motor neurons in adults and in children. Motor neurons are specific types of cells that control voluntary muscle activities such as speaking, walking, and breathing. In adults, symptoms of these disorders often appear after age 40, while in children – particularly in inherited or familial forms of the disease – symptoms may be present at birth.
Motor Neuron Disease generally refers to the diagnosis of Amyotrophic Lateral Sclerosis (ALS), or Lou Gehrig's Disease. In the UK, Motor Neurone Disease refers to both ALS specifically (the most common form of disease) and to the broader spectrum of motor neuron diseases, including Primary Lateral Sclerosis (PLS) and Hereditary Spastic Paraplegia (HSP). In children, MND refers to inherited diseases such as Spinal Muscular Atrophy (SMA).
In order to move a voluntary muscle, usually two motor nerves are involved, an upper motor neuron (UMN), that connects the brain movement areas and the spinal cord, and a lower motor neuron (LMN), that connects the spinal cord with muscles. Motor Neuron diseases are classified based on the major site of motor neuron abnormality. Common MNDs include Amyotrophic Lateral Sclerosis, which affects both upper and lower motor neurons; Primary lateral sclerosis, a disease of the upper motor neurons; Primary Muscular Atrophy, a disease of the lower motor neurons; and Hereditary Spastic Paraplegia, a disease that generally affects upper motor neurons.
Amyotrophic Lateral Sclerosis (ALS)
Amyotrophic Lateral Sclerosis (ALS) is a rare disease in which a specific type of cell, called a motor neuron, dies. These cells control movement and as these cells are lost, the body experiences progressive weakness of the limbs, facial muscles, and diaphragm, while sensory functions – such as sight, smell and taste – remain intact.
In the United States, approximately 5,000 people every year will be diagnosed with ALS, and about 25,000 people currently live with the disease.
The average age of ALS onset is approximately 55 years, although the distribution is broad enough that ALS can be seen in teenagers and adults 80 years and older.
Most cases of ALS occur in the absence of a family history of the disease (sporadic ALS), though five to ten percent of patients inherit the disease (this is known as familial ALS). In most cases of familial ALS, the disease is passed on in an “autosomal dominant pattern;” this means that you only need to get the abnormal gene in order for you to inherit the disease. Often, one parent may have already been diagnosed. In some of these cases, the cause of the disease has been traced to a specific abnormality in the gene that encodes an enzyme called superoxide dismutase 1 (SOD1). The current treatment of ALS is focused on managing symptoms and maintaining strength and the best possible quality of life, as there is no cure for the disease.
Primary Lateral Sclerosis (PLS)
Primary Lateral Sclerosis (PLS) is a rare, neurological disease that affects the upper motor neurons in the brain resulting in increasing muscles stiffness and weakness that usually starts in the legs. PLS is sometimes referred to as a “benign” variation of ALS because it tends to progress slowly. Unlike in ALS, in PLS there is no muscles wasting, as spinal motor neurons or lower motor neurons stay intact.
PLS does not usually run in families and the age of onset is generally between 35 and 66 years of age. The treatment of PLS is focused on symptom relief, as nothing is available at this time to prevent, slow, stop, or reverse the disease.
Hereditary Spastic Paraplegia (HSP)
Hereditary Spastic Paraplegia (HSP) is a group of rare, inherited neurological disorders whose primary symptoms are progressive muscles weakness and increased muscle stiffness (spasticity) that usually starts in the legs . Approximately 30 different types of HSP exist, and it is estimated that there are 10,000-20,000 people in the United States living with the disorder.
HSP is identified by difficulty walking due to increasingly weak and stiff muscles. Initial symptoms may include difficulty with balance, and, as the disease progresses, assistance may be needed. Other common symptoms of HSP are hyperactive reflexes, involuntary muscular contractions and relaxations (known as clonus), and congenital foot problems such as pes cavus (high arched foot). While HSP usually runs in families, even within the same family the severity of symptoms and the exact age of symptom onset can differ. Treatment of HSP is focused on symptom relief, as no treatments are available at this time to prevent, stop, slow, or reverse the disease.
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