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Abnormal smallness of the brain.
[micro- + G. enkephalos, brain]
Farlex Partner Medical Dictionary © Farlex 2012


An abnormally small head, which is usually associated with neurodevelopmental delay and mental retardation. A standard definition is any brain or head which is ≥ 3 standard deviations below the mean for a person’s age, sex, height, weight and race.

Conditions associated with microcephaly
Cockayne, Miller-Dieker, Smith-Lemli-Opitz, Rothmund-Thomson, and Wolf-Hirschhorn syndromes; chromosomal defects (cat-cry or 5p- and trisomy 13 syndromes), in utero infection (CMV), rubella, toxoplasmosis, toxic exposure (foetal alcohol and foetal hydantoin syndromes), radiation (the only confirmed congenital defect specifically linked to atomic bomb blasts (i.e., in Hiroshima and Nagasaki)), or trauma.

Genes linked to microcephaly
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.


Abnormal smallness of the brain.
Synonym(s): microencephaly.
[micro- + G. enkephalos, brain]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
References in periodicals archive ?
had a younger sister with microencephaly who had also had ESRD for several years.
Pervasive hyperactivity and long-term learning impairments in rats with induced microencephaly from prenatal exposure to methylazoxymethanol.
The combination of microencephaly, cerebellar hypoplasia and hypoplasia of the corpus callosum in humans has been linked to autosomal recessive mutations in genes such as TUBA1A and RELN (ROSS et al., 2001).
Microcephaly is defined as having a small head relative to body size and is based on the ratio of body weight to head circumference or height-to-head circumference (not to be confused with microencephaly, which refers to the size of the brain).
Microencephaly, defined in animal subjects as having a small brain relative to body size, is a gross neuroanatomical anomaly associated with heavy alcohol exposure during development.
Using state-of-the-art three-dimensional stereological techniques, researchers can estimate the volume (size) of various brain regions to demonstrate microencephaly. Many of these stereological studies have demonstrated that developmental alcohol exposure leads to reductions both in brain weight and volume in a rat model (Maier et al.
The resulting deficits can range from gross structural abnormalities, such as small brain size (i.e., microencephaly) with significantly altered brain circuitry (e.g., shrinkage or even complete abs ence of the corpus callosum (1)), to the more subtle, but nonetheless significant, loss of specific nerve cells (i.e., neurons) in a particular brain region.
Blood alcohol concentration and microencephaly: A dose response study in the neonatal rat.
The CNS defects--which include reduced brain size (i.e., microencephaly), reductions in the volume of various brain regions (e.g., in the anterior cerebellum [1] and the corpus callosum [2]) and behavioral impairments (e.g., learning difficulties and attention deficits) (Roebuck et al.