Tachyarrhythmia. Very rapid heart beats.

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

Testicular (or gonadal) atrophy. Condition in men in which the reproductive organs (testes) shrink and may lose function.

Tetranucleotide repeats. As related to myotonic dystrophy, the series of 4 chemicals (abbreviated CCTG and found in the DNA of the ZNF9 gene, on the 3rd chromosome) that repeats itself more times than normal and causes myotonic dystrophy type 2.

Tracheotomy. The implantation of a tube into the trachea to assist patient with breathing; inserted through neck just below the thyroid gland.

Trinucleotide repeats. As related to myotonic dystrophy, the series of 3 chemicals (abbreviated CTG and found in the DNA of the DMPK gene, on the 19th chromosome) that repeats itself more times than normal and causes myotonic dystrophy type 1.