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Allele: Any one of two or more genes occupying the same location on a chromosome, determining a given trait (such as eye color, production of a particular enzyme, etc.).

Amniocentesis: Withdrawal of fluid from the amniotic sac, the innermost membrane surrounding the fetus containing amniotic fluid. Can sometimes be used to obtain samples for prenatal diagnosis of certain LSDs.^[1,2]

Angiokeratoma: Purplish-blue skin rash that may be a symptom with several LSDs.

Asymptomatic: Descriptive term for a person who does not appear to be affected by their disease (i.e., displays no symptoms); in context of genetic diseases the person may be a carrier.

Autosomal recessive disorder: A genetic disease caused by a gene mutatation on an autosome (non-sex-related chromosome), caused when an individual inherits the mutated gene from both parents.

Bone marrow transplant: See hematopoietic stem cell transplant (HSCT).

Carrier: A person who possesses at least one gene that may contribute to disease in offspring. Carriers may not develop the disease themselves, but they can transmit it by passing the mutated gene (or genes) to their offspring. (Synonym for heterozygote.)

Cell: The smallest structural unit of the body, capable of performing all the key functions of life (digestion, reproduction, waste disposal, etc.).

Chorionic villi: Tiny membrane projections in the developing placenta (the tissue that connects the umbilical cord to the uterus). Cells samples can sometimes be obtained from the chorionic villi and used for prenatal diagnosis of certain LSDs.[3]

Chromosomes: Structures made up of strands of DNA molecules and associated proteins and containing the genes that define a person's bodily makeup (e.g., hair and eye color, disease expression, etc.). Every cell in the body contains an identical set of 46 chromosomes, grouped into 23 pairs.

Congenital: Existing at birth; referring to certain mental or physical traits, malformations, or diseases, which may be hereditary or due to an influence occurring during gestation (in utero).

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DNA (deoxyribonucleic acid): Chemical molecules that contain all a person’s genetic materials and from which chromosomes and genes are constructed.

Dominant: A genetic trait that is expressed even if only one gene in the pair code for it; it will “override” a gene that codes for a recessive trait.

Enzyme: A type of protein that facilitates chemical changes in other substances. LSDs are caused by the deficiency or malfunction of certain enzymes in the body.

Enzyme assay: Definitive test used to diagnose most LSDs. Enzyme levels are analyzed in a tissue sample taken from the patient and compared to known normal levels. Lower-than-normal levels for certain enzymes provides a conclusive diagnosis for the LSD associated with the enzyme.[4,5]

Enzyme replacement therapy (ERT): A form of treatment used for some LSDs in which patients get an intravenous infusion to replace the missing or faulty enzyme causing the LSD.

Genes: Pieces of DNA that occupy specific locations on chromosomes and that control different activities and details of a person's makeup and function (e.g., eye color, production of certain enzymes, etc.).

Gene therapy: Potential treatment for LSDs, currently in experimental stages, that involves replacing the patient’s mutated gene with a normal copy.

Genetic: Affecting or affected by genes (such as a genetic disease); genetic material is inherited by children from their parents.

Genetic counselor: An expert in genetic disorders who provides information about the risk and difficulty of a disorder to patients or relatives in families with genetic disorders as an aid to making informed decisions about marriage, children, early diagnosis, and prognosis.

Geneticist: A physician who specializes in genetics, the study of heredity and variation of organisms.

Genotype: The genetic make-up of an individual's cells. The genotype together with the biologic environment produce the phenotype, or the outward manifestations.

Hematologic: Of or pertaining to the blood and bone marrow.

Hematopoietic stem cell transplantation (HSCT): A form of treatment used for some LSDs in which healthy stem cells (usually taken from bone marrow, sometimes from cord blood)[3] are intravenously transplanted into a patient to produce the faulty or missing enzyme (and create additional healthy cells).

Hepatomegaly: Enlargement of the liver; may be a symptom with several LSDs.

Hepatosplenomegaly: Enlargement of the liver and spleen; may be a symptom with several LSDs.

Heterozygote: See carrier.

Hypertrophy: The enlargement or overgrowth of a part or organ, not due to tumor formation. Hypertrophy denotes greater bulk through increase in size, but not in number, of cells or other individual tissue elements.

Hypotonia: A condition of diminished tone of the skeletal muscles, and the reduced resistance of muscles to passive stretching; may be a symptom with several LSDs

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Infusion: The introduction of a fluid other than blood into a vein, often over a long period of time. Many medicines (including enzyme replacement therapy) are administered by infusion.

Intravenous: A word meaning "within a vein or veins." Used to describe an injection into a vein to provide nutrition, water, or medication. Infusions are given intravenously.

Lipid: A type of fat molecule. Lipids are important components of cellular membranes, but may accumulate as waste material if not broken down by enzymes.

Lysosome: A specialized component (organelle) of a cell that contains enzymes for breaking down waste molecules.

Lysosomal storage disorders: A class of genetic disorders caused by the deficiency or malfunction of specific enzymes found in cell lysosomes, causing accumulation of waste material in cells.

Macroglossia: Enlargement of the tongue; may be a symptom with several LSDs.

Metabolic: Relating to metabolism, a term used to describe the chemical and physical changes that occur in the body when molecules are either broken down or built up in cells and tissues.

Molecule: The smallest particle of a substance that retains all the properties of the substance and is composed of one or more atoms.

MRI (magnetic resonance imaging): Medical imaging that allows a noninvasive view of the internal organs, including bone marrow. Sometimes used to aid in the monitoring of LSDs.[1]

Mutated gene/mutation: A gene that has changed (mutated), affecting normal transmission and expression of the trait that gene controls.

Neurologic: Of or relating to the central nervous system.

Neuromuscular disorder: A disorder involving the relationship between nerves and muscles, and especially the weakening or dysfunction of the muscles.

Neuronopathic: A word used to describe a disorder that affects the brain or nervous system. Many LSDs have both neuronopathic and non-neuronopathic types.

Nucleus: The cell’s “command center,” containing all a person’s genetic material.

Organelle: Smaller components within cells responsible for carrying out various functions of the cell (reproduction, consumption, waste disposal, etc.)

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Pan ethnic: Affecting people of any ethnic background. Most of the LSDs are panethnic, but some of them are more common in certain ethnic groups.

Pathogenesis: The underlying origin or cause of a disease.

Phenotype: The outward manifestations (e.g., eye color, disease symptoms, etc.) that result from the genotype (the genetic material), sometimes in interaction with the biologic environment.

Physical therapist: A specialist trained in the treatment of diseases and injury through exercise and physical activities; may be involved in addressing some LSD symptoms.

Protein: The building blocks of cells involved in all essential life functions (e.g., cell growth, energy production, metabolism). Enzymes are a type of protein.

Pubertal delay: A lack of the signs of puberty in either sex by age 14. Delayed puberty and other growth-related problems or delay can be symptoms related to many LSDs.

Receptors: Specialized structures, often on the surface of cells, that recognize molecules for signaling or for transporting into the cell.

Recessive: A genetic trait that is only expressed if both genes in the pair code for it; it can be “overridden” if the other gene in the pair codes for a dominant trait.

Recombinant DNA technology: A procedure for manufacturing proteins by manipulation of DNA segments. Used to produce large quantities of enzymes for use in enzyme replacement therapy.

Red blood cell: A cell in the blood of vertebrates that transports oxygen and carbon dioxide to and from the tissues; in mammals it contains hemoglobin.

Ribonucleic acid (RNA): A nucleic acid that helps transfer information from DNA to the protein-forming system of the cell.

Renal: Of or pertaining to the kidney.

Small molecule drugs: Form of LSD treatment that attempts to use small molecules to administer therapies to stabilize faulty enzymes or minimize the amount of waste material that accumulates.[5,6]

Splenomegaly: Enlargement of the spleen; may be a symptom with several LSDs.

Substrate: Waste material that may accumulate in cell lysosomes when it is not broken down by enzymes.

Symptom management: Care for LSD patients that tries to alleviate and manage their symptoms with a variety of methods (surgery, drugs, dialysis, transplantation, etc.), but does not affect the underlying cause of the disease. (Synonym for palliative or supportive care.)

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White blood cells: A group of cells that are involved in protecting the body from infection and invasive foreign materials.

X-linked recessive disorder: A genetic disease caused by a gene mutation on an X chromosome (one of the chromosome that determines a person’s gender), caused when a male inherits the mutated gene from his father or (more rarely) when a woman inherits it from both parents.

X-ray: Electromagnetic radiation of short wavelength used to penetrate tissues and record densities on film. Sometimes used to aid in diagnosis of LSDs.[1]

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1. Wilcox, WR. Lysosomal Storage Disorders: The Need for Better Pediatric Recognition and Comprehensive Care. Journal of Pediatrics; May 2004: S3-S14.

2. Meikle, PJ, et al. Prevalence of Lysosomal Storage Disorders. JAMA; 1999: 281: 249-254.

3. Muenzer, J. The Mucopolysaccharidoses: A Heterogeneous Group of Disorders with Variable Pediatric Presentations. Journal of Pediatrics; May 2004: S27-S34.

4. Wenger, DA. Insights into the Diagnosis and Treatment of Lysosomal Storage Diseases. Arch Neurol; 2003: 60: 322-328.

5. www.pitt.edu/AFShome/g/e/geneorb/public/html/courses/lyso_trials/lsd.html

6. Desnick, RJ, Schuchman, EH. Enzyme Replacement and Enhancement Therapies: Lessons from Lysosomal Storage Disorders. Nature Reviews - Genetics. 2002; 3: 954-966.