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Overview

AHC is a rare and complex neurological disorder—one that families, caregivers, and professionals often must learn about quickly and deeply. This resource hub was created to make that journey easier. Here, you will find a curated collection of trusted information, educational tools, scientific insights, and community‑driven perspectives designed to help you better understand AHC and the people it affects. Whether you are newly navigating a diagnosis or seeking to expand your expertise, these resources offer clarity, connection, and hope as you learn more about this extraordinary, rare disease.

AHC Definitions By Symptom

Below are some common terms used to describe AHC symptoms along with their definitions to be easily understood by families, teachers, therapists, caregivers, and friends.

  1. Paroxysmal – is an episode of uncoordinated movement that occurs occasionally and then stops.
    1. Abnormal Ocular Movements (Eyes)
      1. Nystagmus – Rapid, involuntary movements of the eye. Movements may be horizontal (side-to-side), vertical (up and down) or rotary (circular).
      2. Esotropia – A form of strabismus in which one or both eyes turn inward. The condition can be constantly present, or occur intermittently, and can give the affected individual a “cross-eyed” appearance.
      3. Exotropia – A form of strabismus where the eyes deviate outward.
    2. Dystonia – involuntary repetitive twisting and sustained muscle contractions. These result in abnormal movements and postures.
    3. Ataxia – a lack of muscle coordination which may affect speech, eye movements, the ability to swallow and eat, walking, picking up objects, and other voluntary movements.
    4. Hypotonia – A state of low muscle tone (the amount of tension or resistance to stretching in a muscle), often involving reduced muscle strength.
    5. Bulbar Palsy – Bulbar Palsy is the result of diseases affecting the lower cranial nerves. A speech deficit occurs due to paralysis or weakness of the muscles of articulation which are supplied by these cranial nerves.
      1. Dysarthria – difficult or unclear articulation of speech that is otherwise linguistically normal.
      2. Dysphagia – difficulty in swallowing and chewing food – it takes more effort than normal to transport food from the mouth to the stomach. Drooling may occur as saliva collects in the mouth and they are not able to swallow.
      3. PseudoBulbar Affect – a condition that causes uncontrollable crying and/or laughing that happens suddenly and frequently. A person who has a PBA crying spell may cry when they do not feel sad or when they only feel a little bit sad. Someone having a PBA laughing spell may laugh when they do not feel amused or when they only feel a little bit amused.
    6. Choreoathetosis – ceaseless occurrence of rapid, complex jerky movements that appear to be well coordinated but are performed involuntarily.
  2. Neurological
    1. Motor Function Disorder (Plegia/Plegic means paralyzed – Paresis means weakened)
      1. Monoplegia/monoparesis – only one limb is affected.
      2. Diplegia/diparesis – both limbs are affected; often legs more than arms.
      3. Hemiplegia/hemiparesis – the arm and leg on one side of the body are affected.
      4. Paraplegia/paraparesis – the lower half of the body, including both legs, is affected.
      5. Triplegia/triparesis – three limbs are affected. This could be both arms and a leg, or both legs and an arm. Or it could refer to one upper and one lower extremity and the face.
      6. Double hemiplegia/double hemiparesis – all four limbs are involved, but one side of the body is more affected than the other.
      7. Tetraplegia/tetraparesis – all four limbs are involved, but three limbs are more affected than the fourth.
      8. Quadriplegia – a condition of paralysis in which a person loses complete or partial use of all limbs and the torso.
      9. Pentaplegia/pentaparesis – all four limbs are involved, with neck and head paralysis often accompanied by eating and breathing.
    2. Epilepsy – Epilepsy is a chronic disorder of the brain that causes a tendency to have recurrent seizures.
      1. Focal Onset – The term focal is used instead of partial to be more accurate when talking about where seizures begin. Focal seizures can start in one area or group of cells on one side of the brain.
        1. Focal Onset Aware Seizures – When a person is awake and aware during a seizure, it is called a focal aware seizure. This used to be called a simple partial seizure.
        2. Focal Onset Impaired Awareness – When a person is confused or their awareness is affected in some way during a focal seizure, it is called a focal impaired awareness seizure. This used to be called a complex partial seizure.
      2. Generalized Onset – These seizures affect both sides of the brain or groups of cells on both sides of the brain at the same time.
        1. Motor symptoms
          1. Clonic – sustained rhythmical jerking movements
          2. Atonic – muscles becoming weak or limp
          3. Tonic – muscles becoming tense or rigid
        2. Non-motor symptoms
          1. Absence – staring spells
          2. Myoclonus – brief twitches
      3. Unknown Onset – When the beginning of a seizure is not known, it is now called an unknown onset seizure. A seizure could also be called an unknown onset if it is not witnessed or seen by anyone, for example when seizures happen at night or in a person who lives alone.
        1. Motor – are described as either tonic-clonic or epileptic spasms.
          1. Tonic-clonic
          2. Other motor
        2. Non-motor – usually include behavior arrest. This means that movement stops – the person may just stare and not make any other movements.
      4. Status Epilepticus – a continuous seizure lasting more than 5 minutes, or two or more seizures without fully regaining consciousness in between.
    3. Developmental Delay/Regression – important developmental milestone delay regarding motor, speech and language, cognition, social functioning, and activities of daily living.
    4. Mood Disorders – a group of diagnoses where a disturbance in the person’s mood is an underlying feature.
      1. Depression – Depressed mood or a loss of interest or pleasure in daily activities for more than two weeks. • Mood represents a change from the person’s baseline. • Impaired function: social, occupational, educational.
      2. Anxiety – An excessive anxiety and worry (apprehensive expectation), occurring more days than not for at least 6 months, about several events or activities (such as work or school performance).
      3. Social Phobias – A persistent fear of one or more social or performance situations in which the person is exposed to unfamiliar people or to scrutiny by others. The individual fears that he or she will act in a way (or show anxiety symptoms) that will be embarrassing and humiliating.
      4. Bipolar Disorder – (formerly called manic-depressive illness or manic depression) is a mental illness that causes clear shifts in a person’s mood, energy, activity levels, and concentration.
      5. Psychosis – a disturbance that involves the sudden onset of at least one of the following positive psychotic symptoms: delusions, hallucinations, disorganized speech (e.g., frequent derailment or incoherence), or grossly abnormal psychomotor behavior, including catatonia.
    5. Executive Functions – consists of several mental skills that help the brain organize and act on information. These skills enable people to plan, organize, remember things, prioritize, pay attention, and get started on tasks. They also help people use information and experiences from the past to solve current problems.
      1. Impulse Control – ability to stop and think before acting.
      2. Emotional Control – ability to manage feelings by focusing on the result or goal.
      3. Flexibility – ability to roll with the punches and produce new approaches when a plan fails.
      4. Working Memory – ability to hold information in her mind and use it to complete a task.
      5. Self-monitoring – ability to keep track of and evaluate her performance on regular tasks.
      6. Planning and prioritizing – ability to produce the steps needed to reach a goal and to decide their order of importance.
      7. Task initiation – ability to get started on a task.
      8. Organization – ability to keep track of information and things.
    6. Behavioral Manifestations – occurrence of discrete episodes of failure to resist aggressive impulses that result in violent assault or destruction of property.
  3. Peripheral Nervous System
    1. Hypertonia (Spasticity) – Increased tightness of muscle tone and reduced capacity of the muscle to stretch.
    2. Hypotonia – A state of low muscle tone (the amount of tension or resistance to stretching in a muscle), often involving reduced muscle strength.
    3. Autonomic Dysfunction – a deviation from or interruption of the normal function of the autonomic nervous system.
      1. Heart rate (blood pressure)
      2. Body temperature (perspiration)
      3. Breathing rate
      4. Digestion (bowel and bladder functions)
      5. Apnea
      6. Metabolism (body weight)
      7. Balance of water and electrolytes (such as sodium and calcium)
      8. Production of body fluids (saliva, sweat, and tears)
      9. Other symptoms include
        1. Color changes
        2. Pupillary abnormalities
        3. Fatigue
        4. Lightheadedness
        5. Feeling faint or passing out
        6. Impairment in the body’s ability to handle gravity

Sources: Taber’s Cyclopedic Medical Dictionary, Dorland’s Illustrated Medical Dictionary, Stedman’s Medical Dictionary

Road Map to AHC – Human Phenotype Ontology AHC Glossary Gene Therapy Glossary Comparison of AHC Mouse Models Flunarizine Known Mood Disorders AHC Infographics AHC Publication Hub

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