Accommodations. Supports that are provided to a child throughout the school day that do not significantly alter what is being taught or how the child participates in school activities. Examples include preferential seating, extended time on tests, daily communication logs to share information between school and home, use of spell check or a computer, enlarged print, and books on tape.

Activities of Daily Living (ADL). Normal day-to-day activities such as walking, going to the bathroom, eating, dressing, bathing, etc.

Americans with Disabilities Act (ADA). The ADA prohibits discrimination against people with disabilities in employment, transportation, public accommodation, communications, and governmental activities.

Amniocentesis. A method of prenatal diagnosis at 15 weeks in which a fluid sample is removed from the womb and grown in tissue culture; it takes another 2-3 weeks for results; a fetus can be tested for genetic diseases this way.

Ankle Foot Orthosis (AFO). An apparatus used to support, align, prevent, or correct deformities or to improve the function of the ankle and foot.

Anticipation. The tendency in certain genetic disorders-like myotonic dystrophy-for individuals in successive generations to present with symptoms at an earlier age and/or with more severe manifesations; often observed in disorders resulting from the expression of a trinucleotide repeat mutation that tends to increase in size and have a more significant effect when passed from one generation to the next.

Anticholinesterases. (Example: Neostigmine) One of the drugs that myotonic dystrophy patients should avoid; can adversely affect diameter of blood vessels, function of the intestines, and part of the nervous system that controls smooth muscle, heart muscle and gland cells.

Apnea. Periodic absence of breathing while sleeping.

Armodafinil. A drug used to treat excessive daytime sleepiness (brand name is Nuvigil).

Arrhythmia. An irregular heart beat.

Aspiration pneumonia. Serious form of pneumonia resulting from inhalation of foreign material, usually food particles or vomit, into the bronchi.

Asymptomatic. Without symptoms, at least in the mind of the person himself.

Atrial fibrillation. Abnormal heartbeat in which the normal rhythmical contractions of the upper chambers of the heart (cardiac atria) are replaced by rapid irregular twitchings of the muscular wall.

Attention Deficit Hyperactivity Disorder. A behavior disorder originating in childhood in which the essential features are signs of developmentally inappropriate inattention, impulsivity and hyperactivity.  Although most individuals have symptoms of both inattention and hyperactivity-impulsivity, one or the other pattern may be predominant.  The disorder is more frequent in males than females.  Onset is in childhood.  Symptoms often attenuate during late adolesence, although a minority experiences the full complement of symptoms into mid-adulthood.

Autosomal dominant. A pattern of inheritance in which if one parent has a mutated gene, each offspring has a 50% chance of inheriting it.