Advanced paternal age: A man who is age 40 years or older at the time of conception. (There is no universally accepted definition of advanced paternal age but this criterion is often used in genetic counseling.)
Advanced paternal age is associated with an increased risk of new mutations in the offspring. This risk for genetic defects does not increase dramatically at age 40, but rather increases linearly with the age of the father. The risk of genetic defects due to new dominant mutations is 4 to 5 times greater for fathers aged 45 and above than for men in their early twenties.
There are two types of paternal age effects. One relates to the autosomes and the other to the X chromosome. New autosomalmutations for dominant conditions show up in the children. Their diseases are due directly to advanced paternal age.
New mutations on the X chromosome are usually not evident in the children. They are transmitted to daughters who are at risk for having sons with X-linked diseases. This is an indirect paternal age effect; it is the effect of the age of the maternal grandfather.
Examples of autosomal dominant conditions associated with advanced paternal age include achondroplasia, neurofibromatosis, Marfan syndrome, Treacher Collins syndrome, Waardenburg syndrome, thanatophoric dysplasia, osteogenesis imperfecta, and Apert syndrome.
Examples of X-linked conditions associated with increased maternal grandfather’s age include fragile X, hemophilia A (factor VIII deficiency), hemophilia B (factor IX deficiency), Duchenne muscular dystrophy, incontinentia pigmenti, Hunter syndrome, Bruton-type agammaglobulinemia, and retinitis pigmentosa.
Adventitia: The outermost connective tissue covering of any organ, vessel, or other structure. For example, the connective tissue that surrounds an artery is called the adventitia because it is considered extraneous to the artery. “Adventitia” comes from the Latin “adventicius” meaning “foreign, strange, extraneous, coming from abroad or from outside.” Other English words that stem […]
Adventitious: Coming from an external source or occurring in an unusual place or manner. Not inherent, inherited or innate but rather occurring accidentally or spontaneously. When a doctor or nurse auscults (listens to) the chest or abdomen, adventitious sounds are those that are normally not heard coming from the chest or abdomen. The word “adventitious” […]
- Adverse effect
Adverse effect: A harmful or abnormal result. An adverse effect may be caused by administration of a medication or by exposure to a chemical and be indicated by an untoward result such as by illness or death.
- Adverse event
Adverse event: In pharmacology, any unexpected or dangerous reaction to a drug or vaccine.
- Adverse reaction
Adverse reaction: In pharmacology, any unexpected or dangerous reaction to a drug. An unwanted effect caused by the administration of a drug. The onset of the adverse reaction may be sudden or develop over time. Also called an adverse drug event (ADE), adverse drug reaction (ADR), adverse effect or adverse event.