Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

adenine
One of the four bases that make up DNA. Abbreviated with an “A.”
allele
An alternate version of a gene, e.g., Gregor Mendel's pea plants have flowers with two colors: white and purple.
amino acid
A class of molecules that are the building blocks of proteins. There are 20 different amino acids used to make up proteins.
APGAR score
A score used to quickly assess the health of a newborn child immediately after birth, evaluating five simple criteria: appearance, pulse, grimace, activity, respiration.
atrophy
Decreased size of a body part or tissue, typically resulting from tissue loss. Muscle atrophy refers to loss or wasting away of muscle.
autosome
A chromosome that is not involved in sex determination.
axon
The extension of a nerve cell along which nerve impulses travel away from the cell body towards other cells. At the end of an axon there are axon terminals that may form specialized junctions called synapses – places where a nerve impulse is transmitted to another cell (e.g. neurons, muscle, gland cells).

B

base
A small molecular component of the nucleotides that make up DNA and RNA. There are four different bases – adenine (A), cytosine (C), guanine (G), and thymidine (T) – that are arranged in differing sequences in a DNA molecule. RNA molecules use uracil (U) instead of thymidine. The sequence of bases determines the instructions (genetic code) for the sequence of amino acids that form proteins. (see also nitrogenous base)
base pairing
Discovery made by James Watson that was key in solving the structure of DNA. The bases that make up DNA pair with each other: A to T and G to C. The pairs are held together by hydrogen bonds.
BiPAP
Bi-level positive airway pressure (BiPAP), is a type of noninvasive ventilation that uses a mask to help patients to breathe and keep air moving into their lungs.

C

carrier
A healthy individual who “carries” one gene for a disorder but does not have the disease. In the case of SMA, carriers have one abnormal copy of the SMN1 gene and one normal copy of SMN1. Two individuals who each carry the SMA gene have a 25% chance having a child with SMA each time they conceive. A child must inherit two copies of the abnormal SMN1 gene to develop SMA, from copy each parent.
central dogma of biology
The theory developed by James Watson and Francis Crick to describe the process of protein production: DNA to RNA to protein.
chromosome
Packages of DNA found in the nucleus of cells. Humans have 46 chromosomes.
clinical presentation
Clinical presentation is a description of what symptoms or problems a patient is experiencing when go to a doctor or hospital.
codon
Three bases in a DNA sequence that encode the type of amino acid to be placed in the protein during the central dogma of biology. For example, the codon G-T-G signifies the amino acid valine.
cough assist machine
A noninvasive respiratory therapy machine that helps to induce a cough in patients. The patient breathes into a mask attached to a machine. The cough assist can also help to remove secretions (mucous).
cytosine
One of the four bases that make up DNA. Abbreviated with a “C.”

D

DNA (deoxyribonucleic acid)
An organic acid and polymer composed of four nitrogenous bases — adenine, thymine, cytosine, and guanine — linked via intervening units of phosphate and the pentose sugar deoxyribose. DNA is the genetic material of most organisms and usually exists as a double-stranded molecule in which two antiparallel strands are held together by hydrogen bonds between adenine-thymine and cytosine-guanine.
deletion
A mutation in DNA where a section of DNA is deleted. Some deletions have no effect while others can have a drastic effect, depending on how much DNA is deleted and whether the deletion is in a region of DNA that encodes a protein.
deoxyribonucleic acid
(see DNA)
dominant trait
A genetic trait is dominant when only one copy of the gene is necessary for the trait to develop. A trait is recessive when two copies of the gene are needed for the trait to occur.

D, continued

dominant disorder
A genetic disorder is dominant when only one copy of the abnormal gene is necessary for the disorder to develop. A disorder is recessive when two copies of the abnormal gene are needed for the disorder to develop.
double helix
Describes the coiling of the antiparallel strands of the DNA molecule, resembling a spiral staircase in which the paired bases form the steps and the sugar-phosphate backbones form the rails.

E

eukaryote
An organism whose cells have a nucleus and other membrane-bound vesicles. Examples include higher organisms, such as plants, animals and humans.
exon
A section of a gene that contains the instructions for making a protein.

G

gene
A section of DNA that contains instructions for making a protein.
gene expression
The process of producing a protein from its DNA- and mRNA-coding sequences.
genetic code
The three-letter code that translates nucleic acid sequence into protein sequence. (see also codon)
genome
Refers to all the DNA of an organism; the entire genetic component.
genotype
The structure of DNA that determines the expression of a trait (phenotype).
guanine
One of the four bases that make up DNA. Abbreviated with a “G.”

H

Hammersmith functional motor scale (HFMS)
A test used to evaluate motor function for individuals with SMA Type II and III. Multiple versions of the HFMS are validated and used, including the Expanded and Modified HFMS.
heterozygous
Possessing two different forms (alleles) of a gene, one inherited from each parent. Healthy individuals with one abnormal and one normal allele are known as gene “carriers.”
homozygous
Possessing two identical forms (alleles) of a gene, one inherited from each parent.

I

investigational new drug (IND)
A request to the U.S. Food and Drug Administration for authorization to administer an experimental drug or biological product to humans. This application precedes the start of human clinical trials.
insertion
A mutation in DNA where a section of DNA is inserted. Some insertions have no effect while others can have a drastic effect, depending on how much DNA was inserted and whether the insertion was in a region of DNA that encodes a protein.
intron
A section of a gene that does not contain any instructions for making a protein. Introns separate exons (the coding sections of a gene) from each other.

M

Mendelian inheritance
Rules describing the inheritance of traits and genetic disorders, based around dominant and recessive patterns of inheritance.
messenger RNA (mRNA)
A type of RNA involved in protein production. DNA is transcribed into mRNA, which is then spliced to remove introns, then translated into amino acids to form proteins.
motor neuron
A type of nerve cell that conveys impulses from the brain to the spinal cord or from the spinal cord to a muscle. Alpha motor neurons, which are responsible for innervation of skeletal muscle located in the ventral horn of the spinal cord, are primarily affected in SMA.
mutation
A change in the genetic code (the A's, C's, G's and T's) of a gene.

N

nitrogenous bases
The purines (adenine and guanine) and pyrimidines (thymine, cytosine, and uracil) that comprise DNA and RNA molecules. (see also base)
nucleotide
A building block of DNA and RNA, consisting of a nitrogenous base, a five-carbon sugar, and a phosphate group.
nucleus
The membrane-bound region of a eukaryotic cell that contains the genetic material.

O

onset
The first appearance of signs and symptoms of a disease or condition.
operator
A prokaryotic regulatory element that interacts with a repressor to control the transcription of adjacent structural genes.

P

phenotype
The expression of a trait based on the genetic makeup (genotype).
prokaryote
An organism whose cell(s) lacks a nucleus and other membrane-bound vesicles. Prokaryotes include all members of the Kingdom Monera.

R

receptor
A protein molecule that binds one or more specific kinds of signaling molecules (ligands), which causes the receptor to change shape (conformation). This can then cause a loss or gain of protein activity and resultant cellular responses.
recessive trait
A genetic trait is recessive when two copies of the gene are needed for the trait to develop. A genetic trait is dominant when only one copy of the gene is necessary for the trait to develop.
recessive disorder
A genetic disorder is recessive when two copies of the abnormal gene are needed for the disorder to develop. A disorder is dominant when only one copy of the abnormal gene is necessary for the disorder to develop.
repressor
A DNA-binding protein in prokaryotes that blocks gene transcription by binding to the operator.
ribonucleic acid (RNA)
The intermediate molecule in the central dogma of biology, RNA is an organic acid composed of repeating nucleotide units of adenine, guanine, cytosine, and uracil, whose ribose components are linked by phosphodiester bonds. Pre-messenger RNA (mRNA) is spliced to remove introns and form mRNA, which is translated into a protein.
ribosomes
Structures made up of proteins and RNA that are the sites of protein production in the cell. Ribosomes decode messenger RNA (mRNA) and assemble amino acids into proteins based on the mRNA transcript.

S

sex chromosome
Sex chromosomes in the germ cells of most animals and some plants combine to determine the sex and sex-linked characteristics of an individual. Sex chromosomes are usually designated X and Y, with females being XX and males being XY in mammals.
splicing
Processing messenger RNA (mRNA) after transcription to remove introns and join exons to allow translation of mRNA into a protein.

T

template
An RNA or single-stranded DNA molecule upon which a complementary nucleotide strand is synthesized.
thymine
One of the four bases that make up DNA, abbreviated with a “T.” Thymine is replaced by uracil in RNA.
trait
(see phenotype)
transcription
The step in the central dogma of biology when DNA is copied to messenger RNA (mRNA) during protein production.
transfer RNA (tRNA)
A specific class of RNA molecules that carry amino acids to ribosomes for assembly into a protein during translation. There is a specific tRNA for each of the 20 amino acids.
translation
A step in the central dogma of biology through which messenger RNA (mRNA) is used and decoded to produce protein. This happens at the protein-making factories of the cell called ribosomes.

U

uracil
Found in RNA, this pyrimidine derivative pairs with adenine and replaces thymine during DNA transcription.