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α

α-L-fucosidase: One of the enzymes that works within the lysosome. A deficiency of α-L-fucosidase prevents the breakdown of fucose, causing it to build up in the body.
α-N-acetylglucosaminidase: One of the enzymes that works within the lysosome. A deficiency of α-N-acetylglucosaminidase prevents the breakdown of heparan sulfate, causing it to build up in the body.

β

β-hexosaminidase: One of the enzymes that works within the lysosome. A deficiency of β-hexosaminidase prevents the breakdown of GM2 ganglioside, causing it to build up in the body.

A

ADL (Activities of Daily Living): The essential self-care tasks of everyday life, such as eating, dressing, bathing, toileting, and moving around.
Angiokeratoma: Small, reddish-purple bumps on the skin seen in some lysosomal storage diseases. They are caused by the swelling of tiny blood vessels near the skin’s surface.
Assistive devices: Equipment designed to help compensate for a lost or weakened body function. Examples include eyeglasses, prosthetic limbs, hearing aids, seating positioners, and wheelchairs.
Autosomal recessive inheritance: A pattern of inheritance where a person develops a disease only if they inherit two copies of the gene with a disease-causing change, one from each parent. The genes are located on the autosomes.

B

Biomarker: A measurable substance in the body, such as in blood or urine, that serves as an indicator of a disease’s status or an effect of a treatment. Measuring the levels of specific biomarkers can help monitor disease progression and provide information on how well a therapy is working.
Blood-brain barrier (BBB): A specialized barrier system that regulates the transfer of substances from the bloodstream to the brain.

C

Carrier: A person who has a change in a gene for a specific disease but does not develop the disease themselves. For example, in an autosomal recessive disorder, a person with this gene variant in only one of their two copies of a gene is called a carrier.
Cherry-red spot: A finding in an eye exam where the central part of the retina (the light-sensitive screen at the back of the eye) appears cherry-red.
Children with medical complexities: Children who require daily support to manage their health conditions.
Corneal clouding: A condition where the cornea, the transparent membrane covering the front of the eye, becomes hazy or opaque. It can lead to decreased vision and sensitivity to light.

D

Definitive diagnosis: The final, confirmed diagnosis of a disease, determined after considering all the results from physical exams and medical tests.
Differential diagnosis: The process of distinguishing between two or more diseases with similar symptoms. It involves using various tests to narrow down the possibilities and arrive at the correct diagnosis.
Dysphagia (Swallowing disorder): A condition where it becomes difficult to swallow food and liquids properly. Because food can enter the windpipe and cause pneumonia (aspiration pneumonia), management may include modifying food textures and rehabilitation therapy.

E

Enzyme activity assay: A test that measures the function of enzymes in the blood or cells. Since lysosomal storage diseases are caused by deficient enzyme activity, measuring which enzyme has low activity helps to diagnose the specific condition.
Enzyme replacement therapy (ERT): A treatment method that replenishes a deficient enzyme in the body, typically through intravenous (IV) infusions. It is often referred to by its abbreviation, ERT.

G

Ganglioside: A type of lipid found mainly on the surface of nerve cells that plays a crucial role in maintaining normal nerve function.
Gene: A specific segment of DNA that contains the instructions for building a particular protein. The DNA is packaged into structures called chromosomes, which are located inside our cells. Humans have 46 chromosomes, organized into 23 pairs. These consist of 22 pairs of autosomes (44 in total) and one pair of sex chromosomes (2 in total).
Gene therapy: A treatment method that introduces a healthy copy of a gene into a patient’s body to treat the genetic changes that cause a disease.

H

Hearing loss: A condition where the ability to hear is reduced. It includes sensorineural hearing loss, caused by damage to the inner ear, cochlear nerve, or brain, and conductive hearing loss, caused by problems in the outer or middle ear.
Hematopoietic stem cell transplantation (HSCT): A treatment that involves transplanting hematopoietic stem cells—the cells that become red blood cells, white blood cells, and platelets—from a donor. This includes bone marrow transplantation and umbilical cord blood transplantation. In lysosomal storage diseases, this is done with the hope that the transplanted donor cells to produce enzyme-making cells in the patient.
Heparan sulfate: A type of mucopolysaccharide (glycosaminoglycan).
Hepatosplenomegaly: The enlargement of the liver and spleen, two organs located in the abdomen. This is caused by a buildup of substances that the body is unable to break down, which can make the abdomen appear swollen.
Hernia: A condition where an internal organ pushes through a weak spot in the surrounding muscle or tissue. In lysosomal storage diseases, umbilical hernias (at the navel) and inguinal hernias (in the groin) can occur.

J

Joint contracture: A condition where joints, such as elbows, knees, and fingers, become stiff, making it difficult to fully straighten or bend them.

K

Kyphoscoliosis: A condition where the spine curves excessively forward and to the side. Specifically, a forward curve of the spine is called kyphosis, and a sideways curve is called scoliosis.

L

Lysosomal storage diseases (LSDs): A group of disorders caused by the dysfunction of lysosomes, leading to the accumulation of unwanted substances in the body. Many different enzymes work within the lysosome to break down waste products. When one of these enzymes doesn’t work correctly, these materials build up in the cell, leading to various symptoms. There are currently about 60 different types of LSDs.
Lysosome: An intracellular organelle that breaks down proteins, carbohydrates, and lipids no longer needed in the body.

M

Medical care at home: The daily medical support provided at home by family members or caregivers to assist with essential life functions, such as breathing and nutrition. This type of care is distinct from medical procedures that are required to be performed by licensed healthcare professionals like doctors and nurses. This care can include support such as suctioning, tube feeding, and ventilator management.
Mucopolysaccharides / Glycosaminoglycans (GAGs): A group of substances that function as lubricants and adhesives between the body’s cells. They are composed of long chains of sugar molecules, which are normally broken down by over ten different enzymes inside the lysosomes. If one of these crucial enzymes is not working properly, these substances cannot be fully broken down and will build up within the lysosomes.

N

Natural history (of a disease): The typical course a disease takes over time if no specific treatment is given.
Neurodegeneration: A condition where brain and nerve cells gradually break down and lose their function as the disease progresses. As a result, individuals may lose the ability to do things they could once do, like walking or talking, and find it difficult to control their body's movements.
Newborn screening: A public health program that tests babies shortly after birth for certain congenital disorders. A small blood sample is typically taken from the baby’s heel to screen for these conditions.

P

Peer support: The act of people with the same illness, disability, or similar challenges providing mutual support as equals. Patient and family support groups are common venues for peer support.
Pharmacological chaperone therapy (PCT): A treatment approach to stabilize the unstable enzyme and help it function effectively.
Prognosis: The medical forecast for the likely course and outcome of a disease.
Psychomotor developmental delay: A condition where a child’s development in language, learning, and motor skills is progressing more slowly than the typical age range for acquiring these abilities.

R

Reasonable accommodations: Providing practical adjustments and support for a person with a disability in response to their stated needs, as long as it does not impose an undue burden. Examples include allowing a student who uses a wheelchair to use a guest elevator to move between classrooms, and permitting a student who has difficulty concentrating due to ambient noise to wear earmuffs during a test.
Respite care: A support service that provides temporary relief for family members who are primary caregivers at home, allowing them to take a break and recharge mentally and physically.

S

Siblings (of children with medical needs): A child who has a brother or sister with a chronic illness, disability, or significant medical needs.
Substrate reduction therapy (SRT): A treatment approach that slows the production of the substance causing lysosomal storage disease, thereby helping to reduce its buildup in the body.
Susceptibility to infection: A condition where the body’s ability to defend against disease-causing bacteria and viruses is weakened for some reason.
Symptomatic therapy / Supportive care: Treatment or care that focuses on relieving distressing symptoms (such as fever, pain, or seizures) rather than curing the underlying cause of the disease.

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