504 plan: Refers to Section 504 of the Rehabilitation Act and the Americans with Disabilities Act, which makes it illegal to exclude people with disabilities from participating in federally funded programs, including many schools. A 504 plan allows students with disabilities to have special accommodations to help them at school.

Acidosis: A decrease in pH arising from accumulation of acid or depletion of alkaline reserves in the blood and tissues, or the condition caused by this process.

Apoptosis: Cell deletion or programmed cell death.

Cysteamine: Cysteamine bitartrate is a cystine-depleting medication that works to reduce the toxic accumulation of cystine in the cells. Currently, cysteamine for nephropathic cystinosis comes in two forms: immediate release, which is administered four times a day (every 6 hours); and delayed release, which is administered two times a day (every 12 hours).

Cystine: One of 21 essential amino acids produced through digestion or acid hydrolysis (chemical breakdown) of proteins.

Dialysis: A medical treatment that removes waste products and extra fluid from the body. Dialysis is necessary when the kidneys are not able to adequately filter the blood. There are two types of dialysis: hemodialysis, which uses an artificial kidney to filter blood; and peritoneal dialysis, which uses a special process to filter blood inside the patient’s body.

Fanconi syndrome: Loss of essential nutrients via urine excretion, including electrolytes (sodium, potassium, bicarbonate), minerals (calcium, phosphate, magnesium), glucose, amino acids, tubular protein including β2-microglobulin, and water.

Hypophosphatemic rickets: Rickets (bone softening) associated with low blood phosphate levels that can have dietary causes but that also arise from dysfunction in renal tubules.

Lysine: One of 21 essential amino acid necessary for optimal growth in infants and for maintenance of nitrogen equilibrium in adults.

Lysosomal storage diseases: A disease in which lysosomal enzymes do not function properly, resulting in a buildup of an unwanted substance in lysosomes.

Lysosome: A cellular “recycling center” in which enzymes break down materials for re-use.

Nephropathic cystinosis: Also called classic infantile cystinosis, this is the most common and most severe form of cystinosis. “Nephropathic” means it is a disease of the kidney. “Infantile” refers to the time of onset. Symptoms of nephropathic cystinosis typically appear within a baby’s first year.

Photophobia: Extreme sensitivity to light.

Renal tubule: Also called tubulus renalis, a renal tubule is a tiny canal in the kidney responsible for reabsorption, secretion, and collection of substances.

White blood cell (WBC) cystine testing: A special blood test that measures how much cystine has built up in the blood cells. A child with cystinosis can have up to 100 times the normal amount.