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A gene is a unit of DNA that codes for the formation of a specific protein. Genes are the fundamental units of heredity. Genes come in pairs: one half of each pair is inherited from our mother, and the other half from our father.

Generalized Seizures

Generalized seizures are thought to involve both sides of the brain at seizure onset. Secondarily generalized seizures begin as partial seizures originating from a specific region of the brain, but very rapidly become generalized.

Genetic Counselor

A genetic counselor is a healthcare professional who has advanced degrees in medical genetics and counseling. Genetic counselors are trained in discussing the genetic components of conditions and genetic test results.

Genetic Disorder

A genetic disorder is a medical condition caused by permanent changes, or mutations, in the DNA sequence of a gene or a number of genes or chromosomes.


A geneticist is a medical doctor who specializes in the diagnosis and care of individuals with genetic disorders.

Germ Line

Germ line refers to the body's reproductive cells, either the egg or the sperm.

Germline Mosaicism

Germline mosaicism is a genetic mutation that arises at the germ line, or gonadal level, meaning that some of either the mother's eggs or the father's sperm cells carry the mutation. The other cells in the body do not have the mutation, and the parent doesn't show any symptoms. TSC results when an egg or a sperm cell that carries the mutation is involved in fertilization.

Gingival Fibroma

A gingival fibroma is a nodular, or lumpy, tumor of the gums.

Glial Cell

A glial cell is a specialized cell that surrounds nerve cells providing structural and metabolic support. It is estimated that glial cells outnumber neurons by as much as 50 to 1. Also known as neuroglia or glia.


Gonadal refers to the body's reproductive organs, either the testicles or the ovaries.

Growth Factor

A growth factor is a naturally occurring protein that stimulates cell growth and division.


Hamartin is the protein coded by the TSC1 gene.


A hamartoma is a collection of abnormally shaped cells that multiplies excessively to form a benign tumor.


Hydrocephalus is a buildup of spinal fluid in the ventricles of the brain, causing intracranial pressure.

Hypomelanotic Macule

Hypomelanotic Macule
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A hypomelanotic macule is a patch of skin lighter than the surrounding area that varies in size from several millimeters to several centimeters in diameter. They also vary in shape but are generally elliptical or lance shaped. Also known as hypopigmented macules or ash leaf spots.


See Individualized Education Plan.

Individualized Education Plan (IEP)

An Individualized Education Plan is a written education plan for a student with learning disabilities that is developed by a team of professionals (teachers, therapists, etc.) and the student's parents. An IEP is based on a multidisciplinary evaluation of the student, describing how the student is currently doing, what the student's learning needs are, and what services the student will need.

Infantile Spasms

Infantile Spasms
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Infantile spasms are a serious type of seizure typically occurring during infancy, usually with onset between five and nine months. The seizures may be identified by a sudden jerking of the body, in which the child flexes or extends at the trunk. The indication may also be more subtle, such as staring or blinking. Infantile spasms commonly appear in clusters, typically occurring as the child is going to sleep, or soon after waking. (For video examples of infantile spasms, see Jacob.)

Intractable Seizures

Intractable seizures are seizures that are difficult to control with antiepileptic medications.

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This content was last reviewed on March 30, 2006.