Glossary of Terms
About This Glossary
This glossary provides definitions for medical and scientific terms commonly used in discussions about Fragile X. Terms are organized alphabetically and grouped by category to help you understand the complex terminology associated with Fragile X conditions.
Using This Glossary
- Terms are organized alphabetically for easy reference
- Each definition includes context specific to Fragile X conditions
- Cross-references are provided where terms relate to each other
- Consult healthcare providers for specific medical questions
A
Genetic Terms
Allele
One of two or more versions of a gene. Each person inherits two alleles for each gene, one from each parent.
Testing & Diagnosis
Amniocentesis
A prenatal diagnostic procedure in which a small amount of amniotic fluid is removed for genetic testing.
Ataxia
Loss of coordination of voluntary muscle movements. A key feature of FXTAS.
Autism Spectrum Disorder (ASD)
A group of developmental disorders characterized by challenges with social interaction, communication, and repetitive behaviors. Common in Fragile X syndrome.
C
Genetic Fundamentals
Carrier
A person who has one copy of a gene mutation. In Fragile X, carriers have the premutation (55-200 CGG repeats).
CGG Repeat
A sequence of three DNA building blocks (cytosine-guanine-guanine) that is repeated multiple times in the FMR1 gene. The number of repeats determines Fragile X status.
Chromosome
A structure in cells that contains DNA. Humans have 23 pairs of chromosomes. The FMR1 gene is located on the X chromosome.
Research & Treatment
Clinical Trial
A research study that tests new treatments or interventions in people.
D
DNA (Deoxyribonucleic Acid)
The molecule that carries genetic instructions for the development and function of living organisms.
Dysmorphic Features
Physical characteristics that differ from typical appearance. In Fragile X, may include elongated face, large ears, and prominent jaw.
F
Core Fragile X Genetics
FMR1 Gene
Fragile X Mental Retardation 1 gene. Located on the X chromosome, mutations in this gene cause Fragile X syndrome and related conditions.
FMRP (Fragile X Mental Retardation Protein)
The protein produced by the FMR1 gene. Absence or reduction of this protein causes Fragile X syndrome.
Full Mutation
More than 200 CGG repeats in the FMR1 gene, causing Fragile X syndrome.
Fragile X Conditions
FXS (Fragile X Syndrome)
The most common inherited cause of intellectual disability and autism, caused by a full mutation in the FMR1 gene.
FXPOI (Fragile X-associated Primary Ovarian Insufficiency)
A condition affecting some female carriers, causing irregular menstrual cycles, infertility, and early menopause.
FXTAS (Fragile X-associated Tremor/Ataxia Syndrome)
A progressive neurological disorder affecting some carriers, typically after age 50, causing tremor, balance problems, and cognitive decline.
G
Genetic Basics
Gene
A segment of DNA that contains instructions for making proteins. Genes are the basic unit of heredity.
Gray Zone
45-54 CGG repeats in the FMR1 gene. Generally not associated with Fragile X conditions but may expand in future generations.
Genetic Services
Genetic Counseling
Professional guidance to help individuals and families understand genetic conditions, inheritance patterns, and testing options.
Genetic Testing
Laboratory analysis of DNA to identify changes in genes. For Fragile X, this involves counting CGG repeats in the FMR1 gene.
H
Hyperactivity
Excessive movement and inability to stay still. Common in individuals with Fragile X syndrome.
Hypermethylation
In Fragile X syndrome, excessive methylation of the FMR1 gene causes it to be "turned off," preventing FMRP production.
I
Intellectual Disability
Below-average intellectual functioning and adaptive behavior. Ranges from mild to severe in Fragile X syndrome.
Intermediate Allele
Same as gray zone; 45-54 CGG repeats.
M
Molecular Genetics
Methylation
A chemical modification of DNA that can turn genes on or off. In Fragile X syndrome, the FMR1 gene becomes hypermethylated.
Mosaicism
Having cells with different genetic makeup. Some individuals with Fragile X have both premutation and full mutation cells.
Mutation
A change in DNA sequence. In Fragile X, refers to expansion of CGG repeats.
N
Normal Allele
5-44 CGG repeats in the FMR1 gene. This is the typical range found in the general population.
Neurodevelopmental Disorder
A condition affecting the growth and development of the brain or central nervous system.
P
Research & Testing
PCR (Polymerase Chain Reaction)
A laboratory technique used to make many copies of DNA for analysis. Used in Fragile X testing.
Penetrance
The likelihood that a person with a genetic mutation will show symptoms. FXTAS and FXPOI have incomplete penetrance.
Clinical Concepts
Phenotype
Observable characteristics resulting from genetics and environment. The Fragile X phenotype includes physical, cognitive, and behavioral features.
Premutation
55-200 CGG repeats in the FMR1 gene. Carriers may develop FXTAS or FXPOI and can pass an expanded mutation to children.
S
Sensory Processing
How the nervous system receives and responds to sensory information. Often atypical in Fragile X syndrome.
Southern Blot
A laboratory technique used to detect specific DNA sequences. Used in Fragile X testing to identify full mutations.
Syndrome
A group of symptoms that consistently occur together and characterize a particular condition.
T
Tremor
Involuntary shaking movement. Intention tremor (shaking during purposeful movement) is characteristic of FXTAS.
Trinucleotide Repeat
A sequence of three DNA building blocks repeated multiple times. CGG is the trinucleotide repeat in the FMR1 gene.
X
X-Linked Inheritance
X Chromosome
One of two sex chromosomes. Females have two X chromosomes; males have one X and one Y. The FMR1 gene is on the X chromosome.
X-linked
A pattern of inheritance for genes located on the X chromosome. Fragile X follows X-linked dominant inheritance with reduced penetrance.
Additional Resources
Genetic Education Resources
For more detailed explanations of genetic terms and concepts:
Note: This glossary provides general definitions. For specific medical questions or clarification about how these terms apply to individual situations, consult with healthcare providers or genetic counselors.