Glossary Terms



Acupuncture is an alternative therapy treatment. It
is an ancient system of Chinese medicine where thin
needles are inserted into specific points
on the body. These points are thought be connected to
specific organ systems. The purpose is to alleviate
various health conditions, including headaches, nausea
and addiction.


Any one of a series of two or more different genes
that occupy the same position (locus) on a chromosome.
In the case of dominant and recessive alleles, the dominant
allele will prevail over a normal allele. A recessive
allele (gene) will usually show it’s trait only if the
corresponding allele on the other chromosome
is also affected, or becomes inactivated or lost.

Amyotrophic Lateral Sclerosis (ALS)

ALS is a rapidly progressive, fatal, neuromuscular disease. Fifty-percent
of ALS patients die from respiratory failure or
pneumonia within three to five years of diagnosis.
The condition is marked by degeneration of the upper
motor and lower motor neurons. It is characterized
by progressive muscle weakness, atrophy, stiffness, spasticity
and fasciculations. Symptoms commonly appear
in middle to late adulthood. There
are some slow progressive forms of ALS. Also called
Lou Gehrig’s Disease, or Motor Neuron Disease.

Amino acid

One of the twenty building blocks of protein. They are
the key components in all living things.


are agents that inhibit the involuntary contractions
of the bladder. They can also help increase the capacity
of the bladder. Anticholinergics are often prescribed
for treating urge incontinence.


A chemical compound or substance that inhibits oxidation.


drugs help reduce spasms, stiffness and cramps. For
PLS and HSP, various types of antispasmodics may be
prescribed to help reduce muscle spasticity and spasms.

(Apparently Sporadic) Spastic Paraplegia (SP)

SP is often a term used when all the signs and symptoms
indicate Hereditary
Spastic Paraparesis
(progressive spasticity and
weakness in the legs), but there is no documented family
history to prove that the disorder is
genetic. Clinicians may diagnose this situation as HSP,
SP or
Primary Lateral Sclerosis
Please see HSP/Heredity.


The progressive loss of muscle mass, or wasting, caused
by reduction in the size or number of muscle cells due
to lower motor neuron damage. It is generally
not a symptom of PLS or HSP, except in rare cases.


An autosome is a chromosome that is not one of the sex-determining
chromosomes. Humans have 23 pairs of autosomes and one
pair of sex chromosomes. The term
autosomal means that the gene responsible for the disorder
is located on one of the autosomes.


The long, hair like extension of a nerve cell that carries
a message to the next nerve cell. Each nerve cell (neuron)
has one axon, which can be over a foot long, and sometimes
many feet long. Nerve cells communicate with each other
by transmitting electrical signals from the branches
at the ends of their axons. They receive signals at
extensions called dendrites.


Babinkski’s signs

A pathological reflex where the great toe extends and
flexes toward the top of the foot and the other toes
fan out when the sole of the foot is firmly stroked.
Babinkski’s signs are commonly seen in PLS and HSP.


The chemistry of biology; the application of the tools
and concepts of chemistry to living systems. Biochemists
study the structures and physical properties of biological


that uses relaxation and visualization to lower stress
levels, alleviate headaches, or reduce blood pressure.
Instruments measure information about bodily processes,
such as muscle tension, skin temperature, brain waves,
and respiration.

Blood-Brain Barrier

The blood-brain barrier is a layer of tightly-packed cells
that line the walls of the blood capillaries in
the brain. It creates a barrier between the brain and
the bloodstream, protecting the brain from substances
in the blood, such as viruses, bacteria, and other toxins.
The barrier keeps diseases and harmful agents away from
the brain, but also prevents many medications from reaching
the brain as well.

Bulbar muscles

The muscles that control the speech, chewing and swallowing.
Bulbar muscles are affected in PLS but rarely in HSP.



A person who has an affected recessive
but usually does not show the effects of that gene because
he or she also has an unaffected gene. Normally, being
a carrier of a recessive disorder is not harmful to
the carrier. Because carriers have one affected gene,
they can pass that gene to their children – however,
unless the other parent is also
a carrier, it is unlikely that any children will be
affected by the disorder, although they may be carriers
as well.


Celebrex is an FDA-approved drug for the treatment of
rheumatoid arthritis, osteoarthritis and pain. Johns
Hopkins University has tested Celebrex in the (ALS)
SOD mouse model. It was shown to extend the life of
the mouse by some 25% as well as protect neurons against
chronic injury by a substance called glutamate.

Central nervous system (CNS)

The brain and spinal cord combined.


The portion of the brain in the back of the head
between the cerebrum and the brain stem. It is responsible
for the coordination of movement and balance.

Cerebro-spinal fluid (CSF)

A watery fluid, continuously produced and absorbed,
which flows in the cavities within the brain and around
the surface of the brain and spinal cord.

Cerebro spinal fluid analysis (spinal tap)

A procedure used to isolate cerebrospinal fluid for
evaluation or diagnosis of disease. The analysis is
normal in HSP and PLS patients.


A treatment method that depends primarily on manipulating
or adjusting the spine to prevent disease and treat
pain and other ailments, such as backaches, tension
and carpal tunnel syndrome.


Chromosomes are self-replicating, genetic structures of cells.
They are located within every cell of the human body
and contain pieces of genetic information (genes) called
DNA. The DNA in each chromosome contains many genes.


Marked by long duration or frequent recurrence.


Clonus is a repetitive jerking of muscles (a series of muscle
contractions) that occurs when there is a disruption
of the signals from the brain that normally inhibit
muscle contractions. This disruption may be due to the
effects of HSP or PLS on stretch reflexes.

Co-Enzyme Q10

Co-enzyme Q10 is a non-prescription dietary supplement
that is involved in a variety of cellular processes.
Some studies show it may be helpful for neurodegenerative

Complicated HSP

Some forms of HSP are considered “complicated”
because they involve additional neurologic symptoms
in addition to progressive spasticity and weakness in
the legs. These conditions include peripheral neuropathy,
ichtyosis (a skin disorder) epilepsy, ataxia, optic
neuropathy, retinopathy, dementia, mental retardation,
deafness, or problems with speech, swallowing or breathing.


The outer layer of the cerebrum, densely packed with
nerve cells.

Cortico-Spinal Tracts

The cortico-spinal tracts, also called the upper motor
neurons, are the long nerves that run from the brain
to the spinal column. They synapse onto spinal
neurons (lower motor neurons) that begin in the spinal
cord and travel to the arms and legs.


Creatine is a dietary supplement that is promoted for
its ability to enhance muscle strength and physical
endurance. A study with ALS mice found that the mice
had significant improvements in their survival with



Not a disease itself, but group of symptoms that
is characterized by a decline in intellectual functioning
that is severe enough to interfere with the ability
to perform routine activities.


Loss of the myelin sheath that surrounds nerves. Loss of myelin is not a factor in
most forms of HSP and PLS.


Extensions from the neuron cell body that take information
to the cell body. A single nerve may possess many dendrites.

Deoxyribonucleic acid



If a particular trait or disorder is produced by a dominant
gene, a person only needs
to have one gene with that trait for it to appear, even
if the other corresponding gene is normal.


DNA stands for Deoxyribonucleic acid, the chemical substance
which stores genetic information in the form of an intertwined,
spiraled double chain, called a double helix. It encodes
the genetic information in the nucleus of the cells,
and determines their structure, function, and behavior.


A speech disorder that is due to a weakness or incoordination
of the speech muscles. Speech is slow, weak, imprecise
or uncoordinated.


The medical term for any difficulty or discomfort when
swallowing. A normal swallow takes place in four stages,
and involves 25 different muscles and five different


Emotional lability

Emotional lability is uncontrolled laughter and crying that does
not reflect how a person actually feels. This condition can affect people
who have diseases or injuries of the brain and nervous system. The exact
cause is unknown, but researchers believe it may result from disruptions
in certain pathways in the brain that are important in expressing or controlling emotions.


Exciting neurons which can over time lead to neuronal



Small, involuntary, irregular, visible contractions
of individual muscle fibers caused by damage to the
lower motor neurons. This symptom is usually not associated
with PLS or HSP since these disorders are primary upper
motor neuron disorders. However, some patients have
minimal lower motor neuron involvement and therefore
report this symptom.


U.S. Food and Drug Administration, the branch of federal
government which approves new drugs for sale.


Occurring within a family. Although this term may be used when
referring to hereditary disorders, the cause may not necessarily
be hereditary. For example, an environmental problem such as exposure
to toxic chemicals may cause a problem with several
members of the same family (and thus be “familial”),
but it is not hereditary.

Familial Spastic Paraplegia

See Hereditary Spastic Paraplegia

Free radicals

Chemicals that are highly reactive and can oxidize other
molecules (i.e. Superoxide).


GDNF (Glial Derived Neurotrophic Factor)

GDNF is a naturally occurring growth factor that
proved capable of protecting and promoting the survival
of motor neurons in animal studies. A growth factor
is a growth inducing protein found in the human body.


Pieces of genetic information, stored in codes in DNA,
that carry the instructions for making all of the proteins
a cell needs, and which determine traits such as hair
and eye color. Genes contain the hereditary information
that is passed on from parents to children when the
sperm and egg, containing the genetic information from
each parent, are combined during conception.


All the genetic material in a particular organism that is
contained in the chromosomes. The “human genome”
is the collection of genes that is necessary to make
a human being.


Glutamate is one of the most common amino acids found
in nature and is present in most tissues. It plays an
essential role in human metabolism. It is a primary
excitatory neurotransmitter in the human CNS, L-glutamate
is present at a majority of synapses. Over-stimulation
of these same receptors is thought to trigger the neuronal
damage associated with a wide variety of neurological
insults and diseases, including amyotrophic lateral
sclerosis and Alzheimer’s disease.

Glutamate toxicity

Toxicity resulting from excess glutamated synapse.

Growth factor

A naturally occurring protein chemical that stimulates
cell division differentiation and proliferation. It
is produced by normal cells during embryonic development,
tissue growth and wound healing.



A trait or disorder that is inherited from the parents
through genetic information.

Hyperactive Reflexes, hyperreflexia

Under normal circumstances, the stretch
receptors in muscles and tendons send reflexes
to the spinal cord and brain telling them when a muscle
is stretched. A signal is automatically returned to
the nerves that control the muscles, telling them to
contract. Under normal circumstances, the brain sends
signals to control and reduce the contraction reflex.
In some cases, there is a disruption of those signals,
resulting in hyperactive reflexes, in which the reflex
is greatly exaggerated. This is a common symptom of HSP and PLS.


Weak or absent muscle response when a normal stimulus is

Hereditary Spastic Paraplegia (HSP)

HSP is a term for a group of inherited primary upper motor
neuron disorders that cause progressive spasticity (stiffness)
and weakness of the leg and hip muscles. There
are at least twenty types of HSP. Rare forms cause additional
neurological symptoms as well. See HSP.


One of the original alternatives to conventional medicine,
homeopathy uses small, diluted doses of substances that
cause illnesses as a means of curing them.


The use of water, from sources such as natural springs,
seaweed baths, or mud baths, as medical treatment. Other
forms of hydrotherapy include ice packs, whirlpool baths,
steam baths, and saunas. Hydrotherapy can be used to
treat stress, headaches, muscle aches, arthritis and



A skin disorder causing dry, rough, scaly skin that may
be a symptom in some forms of complicated HSP.


Incidence is commonly measured in new cases per 1,000
(or 100,000) of population at risk, per year. Due to
rarity and diagnosis inconsistencies, however, it is
difficult to estimate an accurate incidence rate for
HSP and PLS. The incidence of HSP is estimated at 20,000
in the United States, and for PLS, 500. Researchers
feels these are underestimates.

Immune system

A complex system that is responsible for distinguishing
us from everything foreign to us, and for protecting
us against infections and foreign substances. The immune
system works to seek and kill invaders.


Injection into the innermost membrane surrounding the
central nervous system. Usually done by lumbar puncture.


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The site on a chromosome where the gene for a particular
trait is found. Any one of the alleles for a gene may
be found at this site.

Lower motor neuron

Nerve cells starting at the spinal cord or brain
stem and ending at the muscle fibers. The loss of lower
motor neurons leads to weakness, twitching of muscles
(fasciculations), and loss of muscle bulk (atrophy).


Magnetic resonance imaging (MRI)

A non-invasive procedure that produces a two-dimensional
view of an internal organ or structure, especially the
brain and spinal cord.


The use of touch and various manipulation techniques to
move muscles and soft body tissues to relieve stress,
tension, and pain. There are many touch therapies. Some
considered “bodywork” or somatic psychotherapy
might include the use of energy work, talk, and emotional
release. There are many types of massage and bodywork
that require that practitioners receive advanced training
to practice.


Minocycline is an antibiotic that has been shown to delay onset
and slow progression of symptoms in a mouse model for
ALS. Previous studies have shown the antibiotic protects
neurons from dying in animal models for a variety of
neurologic disorders. It is currently being tested in
human clinical trials of Huntington’s disease.


The mitochondria are the principal energy source of
the cell. Mitochondria convert nutrients into energy
as well as doing many other specialized tasks.


The smallest unit of a substance that can exist alone
and retain the character of that substance.

Motor neuron disease (MND)

A group of disorders in which motor nerve cells (neurons)
in the spinal cord and brain stem deteriorate. ALS (Lou
Gehrig’s Disease) is the most common motor neuron disease,
commonly referred to as Motor Neuron Disease. PLS and
HSP are atypical motor neuron disorders because they
don’t involve lower motor neurons. HSP and PLS are primary
upper motor neuron disorders.

Muscle atrophy

Loss of muscle fiber volume characterized by a visible
decrease in muscle size. This occurs because muscles
no longer receive impulses or signals from nerve cells.
It is not a symptom in HSP and PLS, although muscles
may exhibit atrophy due to misuse.

Muscle cramp

Unexpected, involuntary, painful shortening of muscles. Usually,
a knotting of the muscles is visible. Muscle cramps
(spasms) is common in PLS and HSP.

Muscle weakness

Loss of strength, increased fatigue, loss of coordination
and difficulty with motor skills and lack of ability
to carry out certain skills.


A permanent change, a structural alteration, in the
DNA or RNA. Mutations can be caused by many factors
including environmental insults such as radiation and
mutagenic chemicals. Mutations are sometimes attributed
to random chance events.

Myelin Sheath

The coating on the neurons (nerve cells) that that acts
as an insulator to speed the conduction of nerve impulses.
It is analogous to the insulation coating on an electrical



A bundle of fibers that uses electrical and chemical
signals to transmit sensory and motor information from
one body part to another. See neuron.


A neuron is a special cell that transmits electrical signals.
It consists of a nucleus, a single axon which conveys
electrical signals to other neurons and several dendrites
which deliver incoming signals. A single neuron can
be several feet in length. Neurons receive input from
sensory cells or other neurons, and send a signal to
muscles or other neurons. Neurons that have sensory
input are called “sensory neurons”. Neurons
with muscle outputs are called “motoneurons”,
and those that only connect to other neurons are called

Nervous system

The system of cells, tissues and organs that regulates
the body’s responses to internal and external stimuli.
In vertebrae it consists of the brain, spinal cord,
nerves, ganglia and parts of the receptor and effector


Of, relating to, or affecting both nerves and muscles.

Neuronal receptors

Neurons use chemical signaling mechanisms to communicate
with one another. These impulses are transmitted at
junctions between nerves called synapses. The sending
neuron triggers the release of neurotransmitters (chemicals)
into the synaptic cleft. From there, the transmitters
bind to receptors on the post synaptic or receiving
neuronal cell. These receptors are the gate keepers
of neuronal cells and they open and close to send or
receive chemicals that signals which direct the actions
and reactions of the cell.


If an agent provides protection to any part of the body’s
nervous system, it is said to provide neuroprotection.


The scientific disciplines concerned with the development,
structure, function, chemistry, pharmacology, clinical
assessments and pathology of the nervous system.


Chemical substances that carry impulses from one nerve
cell to another; found in the space (synapse) that separates
the transmitting neuron’s terminal (axon) from the receiving
neuron’s terminal (dendrite).



The time of appearance of the first symptoms of a condition,
prior to seeking diagnosis.


Orthotics are special shoe inserts, splints, or braces that are
used to relieve various gait problems, foot problems,
help increase balance, or take pressure off sore spots
on the feet. Orthotics may be custom-molded for your
feet, or may be pre-formed supports, such as simple
arch supports.

Oxidative stress

Accumulation of destructive molecules called free radicals
can lead to motor neuron death. Free radicals damage
components of the cells’ membranes, proteins or genetic
material by “oxidizing” them-the same chemical
reaction that causes iron to rust. Some patients with
familial ALS have mutations in the gene for superoxide
dismutase type 1 (SOD1). SOD1 normally breaks down free
radicals, but mutant SOD1 is unable to perform this



Muscle weakness.


Loss or impairment of motor function of the legs and lower
part of the body.


An unusual sensation which may include numbness, tingling,
burning, or prickling. It is sometimes described as
“the sensation of pins and needles” or “as
if my leg were asleep”.


The likelihood that a particular gene will result in the disease or disorder. For example,
the BRCA1 breast cancer susceptibility gene, even though dominant, does not have
complete penetrance. The risk of a person with this gene getting breast cancer by age
65 is 80 percent rather than 100 percent. In the case of dominant forms of HSP,
though very high, is not always complete.


The study of drugs and their origin, nature, properties
and effects upon living organisms.


The expression of the genes present in an individual.
This may be directly observable (eye color) or apparent
only with specific tests (blood type). Some phenotypes
such as the blood groups are completely determined by
heredity, while others are readily altered by environmental

Primary Lateral Sclerosis (PLS)

PLS is the term for a group of upper motor neuron disorders
that cause cause progressive spasticity (stiffness)
and weakness in the legs, arms, and speech and swallowing
muscles. See PLS.
Also considered a benign variant of ALS.


Proteins are large molecules required for the structure,
function, and regulation of the body’s cells, tissues,
and organs. Each protein has unique functions. Proteins
are essential components of muscles, skin, bones and
the body as a whole.


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A recessive gene generally requires that both corresponding genes are affected
in order for the disorder to appear. If the person has
one affected gene and one unaffected gene, the disorder
will not appear, but the person is considered a “carrier”
of the gene. Therefore, usually only children who inherit
an affected gene from both parents will show the effects
of the disorder.


The only FDA-approved drug available to treat ALS. It
inhibits glutamate release, and prolongs life approximately
three months. Riluzole is the generic name of Rilutek.


A nucleic acid found in all living cells. The primary
function of RNA is protein synthesis within a cell.
However, RNA is involved in various ways in the processes
of expression and repression of hereditary information.
The three main functionally distinct varieties of RNA
molecules are: (1) messenger RNA (mRNA) which is involved
in the transmission of DNA information, (2) ribosomal
RNa (rRNA) which makes up the physical machinery of
the synthetic process, and (3) transfer RNA (tRNA) which
also constitutes another functional part of the machinery
of protein synthesis.



A hardening within the nervous system, especially of
the brain and spinal cord, resulting from degeneration
of nervous elements such as the myelin sheath.

Sex chromosomes

One of the pair of chromosomes linked to gender, known as the X
chromosome and the Y chromosome. Females have two X chromosomes, males have an X and
a Y chromosome.


Drooling resulting from the lack of spontaneous, automatic swallowing
to clear excessive saliva in the mouth.


Increased muscle tone, resulting in “stiffness”. Often
involves an exaggeration of the tendon reflexes.

Spinal cord

Part of the central nervous system extending from the
brain through the vertebrae of the spinal column. Thirty-one
pairs of spinal nerves arise from the sides of the spinal
cord. The spinal cord carries information from the body
to the brain and signals messages from the brain to
the body.

Spinal-bulbar Muscular Atrophy

An X-linked motor neuron recessive disorder characterized
by slowly progressive skeletal muscle weakness, especially
in the muscles of mouth and throat. Also called Kennedy’s

Spinal Muscular Atrophy

A group of predominantly autosomal recessive motor neuron
disorders characterized by severe hypotonia and muscle
weakness due to lower motor neuron dysfunction.

Sporadic Spastic Paraparesis

See (Apparently Sporadic) Spastic Paraplegia (SP)

Stem cells

Undifferentiated cells that can differentiate into many
different cell types when subjected to the right biochemical
signals. The most versatile stem cells, called pluripotent
stem cells, are present in the first days after an egg
is fertilized by sperm. Researchers believe they can
coax stem cells to become whatever tissues patients
need. Stem cells come from embryos, bone marrow and
umbilical chords.

Stem cell transplant

Transplantation of stem cells from various sources has
provided improvement in animal spinal neurodegenerative
disease models such as stroke, epilepsy, Parkinson’s
and spinal cord injury. Human trials are promising,
but not complete.

Stretch receptors

Nerve endings in muscles and tendons that send messages to
the spinal cord when the muscles are stretched.

Superoxide dismutase (SOD)

An enzyme that destroys superoxide, a highly reactive
form of oxygen. It protects against superoxide damage.
20% of ALS patients have mutations in the gene for copper/zinc
superoxide dismutase type SOD1. SOD1 normally breaks
down free radicals, but mutant SOD1 is unable to perform
this function.


Junctions at which neurons communicate with target cells, such as a
muscle cell or axon of another neuron. A tiny gap between the ends of nerve
fibers across which nerve impulses pass from one neuron
to another; at the synapse, an impulse causes the release
of a neurotransmitter, which diffuses across the gap
and triggers an electrical impulse in the next neuron.



Another term for quadriplegia: paralysis of all four limbs

Therapeutic index

A general way of measuring an effective dose of a drug
and its toxicity.


A genetic trait is any sort of distinguishing quality
that can be inherited, such as hair color or eye color.
Traits are determined by information contained in genes.
While many traits are harmless, others can be harmful,
such as birth defects or other types of physical disorders.


An organism whose sperm or egg contain genetic material
originally derived from an organism other than the parents
or in addition to the parental genetic material.



Most forms of HSP are referred to as “uncomplicated”
HSP because symptoms are confined to the lower body.

Upper motor neurons

Nerve cells (neurons) originating in the brain’s motor
cortex and running through the spinal cord.


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X Chromosome

One of the two sex chromosomes. All humans have one X chromosome. Females have two X
chromosomes, while men have one X chromosome and one
Y chromosome.


A gene that is located on the X chromosome. Females have two X chromosomes, while males have
one X chromosome and one Y chromosome. If the trait is recessive, females
with an affected gene on one X chromosome will not show
symptoms unless the corresponding gene on the other
X chromosome is also affected. Since men only have one
X chromosome, if they have an affected gene, they will
have the disorder, as there is no “normal”
gene to compensate for it.


Y Chromosome

One of the two sex chromosomes. Only males have a Y chromosome. Men have an X
chromosome and a Y chromosome, while females have two X chromosomes.


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The Physician Directory lists of clinics and physicians in 27 states and 3 Canadian provinces that are treating PLS and/or HPS patients and welcome new ones.

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Easy to read reference guide that outlines the most pertinent information about HSP and PLS.

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Medical Terms To Know

Glossary of medical terms often related to HSP and PLS.

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Visual resources that help you understand HSP and PLS.

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