Communicate More Effectively With Your Healthcare Team—
A Glossary of Medical Terms

Arylsulfatase B (ASB). The enzyme, or tiny cellular machine, that people with MPS VI don't have enough of. The enzyme works within the lysosomes of every cell to break down and recycle a specific kind of material—a particular type of complex sugar called glycosaminoglycan, or GAG.

Autosomal recessive. The pattern in which some genetic diseases, including MPS VI, are inherited. If only one parent is a carrier, then the couple's children will not develop the genetic disease. But if both parents are carriers, then each pregnancy has a 1 in 4 chance of producing a child with the genetic disease.

BiPAP (Bilevel Positive Airway Pressure). A method used to treat people with sleep apnea, who temporarily stop breathing (or get more air into the lungs). People using BiPAP wear a mask over their face when they sleep, and every time they inhale, pressurized air from this mask gently pushes its way into the mouth and re-inflates the lungs, effectively starting a new breath.

Bone marrow. The fatty tissue found inside our bones that produces a steady stream of new blood cells—including both red blood cells and white blood cells.

Carrier. A person who carries a defective, or non-working, copy of a gene. Since carriers have only one non-working copy of the gene—and one working copy—they do not have a genetic disease. But they can still pass their non-working copy of the gene on to their child, and if that child also receives a non-working copy of that same gene from the other parent, then the child will develop the genetic disease.

Carrier testing. Medical testing to determine if someone, usually a prospective parent or an adult sibling of a person with a genetic disease, is a carrier of that genetic disease.

Centimeter. A metric unit used to measure length. There are about 2 and a half centimeters in an inch and about 30 centimeters in a foot.

Cornea. The outer layer of material that sits on the front of the eye. Like the windshield of a car, the cornea must be clear in order for the eye to see properly, but in MPS VI the cornea becomes cloudy, causing vision to worsen.

CPAP (Continuous Positive Airway Pressure). A method used to treat people with sleep apnea, who temporarily stop breathing many times per night. People using CPAP wear a mask over their face when they sleep, and for every breathing cycle, pressurized air from this mask helps keep the airways open during inhalation and exhalation.

Dysostosis multiplex. The widespread changes that are seen in the bones of people with various forms of MPS, including MPS VI. These changes are partly responsible for the altered physique and posture seen in people with MPS. Dysostosis multiplex includes changes in the skull, spinal column, pelvis, collar bones, ribs, long arm and leg bones, and bones of the hands and feet.

Echocardiogram. An easy way of looking at the health and function of the heart, by bouncing sound waves off of it as it pumps. Using "echo," a doctor can look to see how strongly the heart is pumping, whether the valves are working correctly, how well the blood is flowing, and whether the walls of the heart are thickened and stiff.

Enzyme replacement therapy (ERT). Treatment of a lysosomal storage disorder by giving the patient the specific kind of enzyme that he or she is missing. This is done by giving the patient an intravenous (IV) infusion containing the enzyme. ERTs are already available for five lysosomal diseases—Gaucher disease, Fabry disease, and MPS I, MPS II, MPS VI.

Enzymes. Tiny, molecule-sized machines that are found in every cell in our body. Our cells contain thousands of different types of enzymes, and each one performs a very specific job that only it can do.

Gene therapy. Treatment of a lysosomal storage disorder or other genetic disease by supplying the affected individual with a new copy of the gene that is damaged, missing, or not functioning properly.

Glaucoma. A medical condition in which the fluid pressure inside the eye increases, damaging the eye and distorting vision.

Glycosaminoglycans (GAGs). A closely related family of complex sugars that build up in the cells of people with different forms of MPS, including MPS VI.

Heart failure. Inability of the heart to pump strongly enough to circulate blood to all parts of the body where it is needed. Heart failure can occur for any number of reasons—for example, because the heart walls are stiffened and scarred; or because the heart valves are damaged, causing blood to go the wrong way when the heart pumps; or because the heart is starved of oxygen.

Heart valves. The structures in a heart which cause the blood to flow in only one direction when the heart pumps. If the valves become damaged, as happens in MPS VI, then the heart's pumping is less efficient, because some of the blood that it is pumping moves the wrong way.

Hematopoietic stem cell transplant (HSCT). A procedure in which the stem cells that manufacture blood cells in a person's own bone marrow, are replaced by fresh cells from another person. The term HSCT can actually mean either of two related procedures: bone marrow transplant, which specifically uses cells from another person's bone marrow, and cord blood transplant, which uses cells from the umbilical cord of a newborn baby. In the case of MPS VI, the purpose of HSCT is to give people their own supply of cells—in this case, white blood cells—that produce the enzyme that they were born without.

Hepatomegaly. Enlargement of the liver, which often occurs in lysosomal storage diseases, including MPS VI.

Hernia. A weakness in the muscle lining of the abdomen or some other organ cavity that causes the lining to bulge out.

HSCT. See hematopoietic stem cell transplant (HSCT).

Hydrocephalus. A dangerous buildup of pressure in the sac of fluid that encloses the brain. It often happens in MPS VI, leading to headache and drowsiness, behavioral changes, and sometimes permanent brain damage.

Inguinal hernia. A weakening of the abdominal muscle lining, causing fluid or internal organs to bulge out (under the skin) in the groin.

Inherited disease. A genetic disease caused by non-working genes, which are passed from parents to their children.

Intravenous (IV) infusion. Administering a drug to a person by infusing it directly into the bloodstream. This is usually done by inserting a line into a vein in the forearm. IV infusions can last anywhere from a few minutes to a few hours, during which time the recipient can, for example, lie on a bed or sit in a chair reading or watching TV.

Liver. A large, fleshy organ found in the abdomen. It performs several vital functions, including breaking down toxins in our food, producing some components of the blood, and storing sugar that comes from the food that we eat.

Lysosomal storage disorder (LSD). An inherited genetic disease in which a person's lysosomes—the microscopic recycling bins in his or her cells—do not function properly, causing unrecycled material to build up inside (be stored inside) the lysosomes. Lysosomes contain many different enzymes that help them break down and recycle complex materials that the body can no longer use. But a person with an LSD is missing one of those enzymes. There are several dozen known LSDs.

Lysosomes. The recycling bins of a cell, where complex materials that the body can no longer use are broken down into pieces that are small enough for the cell to reuse. Lysosomes are able to break things down because they are very acidic (just like our stomachs) and contain many different types of enzymes. Each type of enzyme performs a specific task, breaking down a specific type of material.

Maroteaux-Lamy syndrome. Another name for mucopolysaccharidosis VI (MPS VI). The term Maroteaux-Lamy syndrome comes from the names of the two French scientists who first discovered MPS VI in 1963.

Mucopolysaccharidosis (MPS). A family of 7 closely related inherited diseases. MPS VI is a type of MPS. All forms of MPS are lysosomal storage disorders, in which the lysosomes—the cell's recycling bins—fail to function correctly, causing material to pile up inside the cell. The different types of MPS have many symptoms in common, including growth stunting, skeletal changes, breathing problems, liver enlargement, and a high rate of heart failure.

MPS I. A lysosomal storage disease closely related to MPS VI. People with MPS I and MPS VI look very much alike and suffer many of the same medical problems—with one very important difference: MPS I often involves mental retardation, whereas MPS VI usually does not.

MPS VI. Mucopolysaccharidosis VI, also known as Maroteaux-Lamy syndrome. MPS VI is a lysosomal storage disorder in which cells become bloated with used materials that they cannot recycle.

Optic nerve. The nerve that connects the eyeball to the brain, communicating information to the brain about what the eye is seeing. If the optic nerve is damaged—as can happen in MPS VI— then a person can go blind even if the eyes themselves are still healthy.

Oxygen. The gas that we need to survive. When we breathe, our lungs absorb oxygen and move it into our bloodstream, which then transports the oxygen to where it is needed—pretty much all over the body.

Prenatal diagnosis. Testing an unborn baby for a disease such as MPS VI. This is done by sampling fetal cells from the womb in a minimally invasive way.

Red blood cells. The cells that make up most of our blood, and are responsible for its red color. The purpose of red blood cells is to carry oxygen from our lungs to other parts of our body. Red blood cells are formed in our bone marrow.

Retina. The back of the eyeball, where a picture forms and is transmitted to the optic nerve, which then takes the picture to the brain. In MPS VI, the retina can become damaged, contributing to blindness.

Sinus. A cavity inside the front of the head and face that is connected by air passageways to the nose. People with MPS VI experience frequent infections in their sinuses.

Sleep apnea. A breathing disorder in which a person stops breathing and starts breathing again many times during the night, causing them to sleep poorly and putting them at risk for eventually developing heart problems. People with MPS VI often suffer sleep apnea because of narrow airways that make it hard to breathe.

Spasticity. Involuntary twitching, jerking, or other movement, sometimes caused by a pinched or damaged nerve. People with MPS VI can develop spasticity in both arms and both legs owing to constriction of the spinal cord nerves where they pass through the neck.

Spleen. An organ found in the abdomen. It helps to recycle old red blood cells from the bloodstream. It also helps some of the cells in our immune system to grow and mature.

Splenomegaly. Enlargement of the spleen, which often occurs in lysosomal storage diseases such as MPS VI. The enlargement is caused by a buildup of unrecycled materials in the cells of the spleen.

Tissue-matched. A term that applies to hematopoietic stem cell transplantation (HSCT). Donors of hematopoietic stem cells that are tissue-matched have been carefully selected to reduce the risk of immune rejection—otherwise known as graft versus host disease.

Trachea. Commonly called the "windpipe"—the main air passage that connects our lungs to our mouth. In MPS VI, the trachea often narrows and thickens, making breathing both loud and difficult.

Tracheostomy. A small hole made in the windpipe where it passes through the neck. A small tube is inserted into this hole, giving the trachea a direct connection to the outside world—and to air—through the neck. A tracheostomy is usually made to bypass some blockage higher up that hinders breathing.

Umbilical hernia. A weakness in the muscle that lines the abdomen. This type of hernia causes part of the internal organs—usually part of the small intestine—to bulge out near the belly button.

White blood cells. Immune cells in our bloodstream, whose job is to fight infection and devour damaged or dead cells. When someone receives a bone marrow transplant, their white blood cells are essentially replaced, since the bone marrow is what supplies all new white blood cells.