Genetic and Medical Glossary

Glossary

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There are 22 names in this directory beginning with the letter I.
Ichthyosis
general term for a family of genetic skin diseases characterized by dry, thickened, and scaling skin; various forms are distinguished from one another by extent of scaling and how widely and where the scaling is over the body, by presence or absence and intensity of reddening of the skin (erythroderma), by the mode of inheritance, and by the character of associated abnormalities

Immunoglobulin A (IgA)
antibody that plays a critical role in mucosal immunity

Imperforate anus
inborn abnormality characterized by the absence (anal atresia) or abnormal localization of the anus; rectum or colon may be connected to the vagina or the bladder by a fistula

Imprinting
‘memory’ held by a chromosome as to whether it was inherited from the mother or the father and chemically ‘stamped’ into the DNA; results in chromosomes or genes located on the chromosomes that behave differently, depending on the parent of origin; faulty genes on chromosome 15 cause both Angelman (from the mother) and Prader-Willi syndromes (from the father)

Incidence
the frequency in which a disorder appears in a given population

Infantile spasms
seizure disorder of infancy and early childhood with the onset predominantly in the first year of life characterized by myoclonic seizures, hypsarrhythmia (abnormal, chaotic electroencephalogram), and mental retardation

Informed consent
the right of patients to know the risks of medical treatment and to determine what is done to their bodies, including the right to accept or refuse treatment based on this information; usually refers to participation in a clinical trial

Infra-orbital folds
Elevated ridge(s) of skin starting well below the medial aspect of the lower lid and curves gradually upward toward and/or across the nasal bridge

Inherited
genetic transfer from parents to children

Initiation codon
also called the “start codon,” a codon, composed of the nucleotides AUG, that signals the beginning of a protein-coding sequence in a messenger RNA (mRNA) molecule; in the genetic code, AUG always represents the amino acid methionine

Insertion
type of mutation whereby a DNA sequence is abnormally inserted into a gene, disrupting the normal function and structure of the gene and leading to a chromosomal abnormality

Interrupted aortic arch
congenital heart malformation in which a small section of the aorta is missing, causing a loss of luminal continuity between the ascending and descending portions of the aorta

Interstitial deletion
deletion that does not involve the terminal parts (ends) of a chromosome

Intestinal atresia
broad term used to describe a complete blockage or obstruction anywhere in the intestine

Intestinal malrotation
congenital anomaly of rotation of the midgut in which the gut undergoes a complex rotation outside the abdomen during development

Intrachromosomal duplication
translocation that occurs within a chromosome

Intragenic
being or occurring within a gene

Intron
a segment of a DNA or RNA molecule that does not code for proteins and interrupts a gene-coding sequence or nontranslated sequence; segment of a gene situated between exons that is removed before translation of messenger RNA and does not function in coding for protein synthesis

Inversion
a chromosomal abnormality resulting in a region of the chromosome where the normal order of genes is reversed or the segment of the chromosome has two breaks and “flips over”; both instances can cause the genetic code to be translated (read) wrong

Isochromosome
chromosome that has lost one of its arms and replaced it with an exact copy of the other arm

Isodicentric
extra piece of chromosome that has been duplicated end-to-end like a mirror image

Isodisomy
two identical copies of one of the parental alleles

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