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Cataracts. A film that can form in the eye and cause complete or partial opacity of the ocular lens, or blurry vision; in myotonic dystrophy patients, often posterior subcapsular iridescent cataracts form; they are sometimes referred to as Christmas-tree cataracts.

Cardiac conduction. The electrical impulses that cause the heart to beat.

Cardiomyopathy. Damage to the heart muscle that decreases its ability to pump blood effectively.

Cardiotoxicity. Substance that is harmful to the heart.

CCTG. The abbreviation for “cytosine, cytosine, thymidine, guanine”, the chemicals in the DNA that cause myotonic dystrophy type-2 (on chromosome 3) when they are created in repeats greater than the normal number.

Chorionic villus sampling (CVS). A method of prenatal diagnosis at around 10 weeks into the pregnancy; a biopsy in which a piece of membrane around the embryo is removed using a needle through the abdomen or vagina; results in 1-2 weeks.

Chromosome. One of the bodies (normally 23 pairs) located in the nucleus of a cell that hosts the genes.

Cisapride. (Example: propulsid) A prokinetic drug that should be avoided by individuals with myotonic dystrophy.

Club foot. An inversion of the foot in which only the outer side of the sole touches the ground; also called talipes equinovarus.

CNS. Abbreviation for central nervous system; brain.

Cognitive problems. Difficulties with thinking, learning and memory.

Cohort study. Particular form of longitudinal study that samples a cohort, meaning a group of people who share a defining characteristic, typically those who experienced a common event in a selected period.

Conduction defects. Problems with the electrical impulses that regulate the heart beat.

Congenital. Present at birth.

Contractures. Permanent tightening of muscles causing abnormal joint rigidity.

Copayment. A fixed amount ($20 for example) you pay for a covered healthcare service after you’ve paid your deductible.

CPAP. Acronym for continuous positive airway pressure; a device that delivers air to the nose for easier breathing; often used at night for those with sleep apnea.

Creatine Kinase (CK) levels. An important enzyme in muscle contraction.

CTG. The abbreviation for “cytosine, thymidine, guanine”, the 3 chemicals in the DNA that cause myotonic dystrophy type-1 (on chromosome 19) when they sputter beyond the normal 5-37 repeats found along the rung-looking parts in the double helix that resembles a gracefully twisted ladder. CTG repeat causes DM1.