MICROCEPHALY: A Developmental Disorder
Authors: Akram Tariq Muhammad 
Published: September 2022

Microcephaly is a result of abnormal in utero development resulting in an unusually small head size. The word comes from a New Latin word, termed as microcephalia, and from two Ancient Greek terminologies that translates into small and head. Back in Ancient Roman times, individuals that were known to carry small heads in comparison to a normal sized human head were all showcased as a public display, whereas people with microcephaly have been occasionally traded to multiple freak shows back in European and North American regions in the nineteenth and twentieth centuries, in which they were regarded as pinheads or freaks of the nature while a lot among them were showcased as a completely different species and were referred to as the lost connection in the evolution process. Growth limitation impacts the Central Nervous System (CNS) and brain in the more serious forms of cases, which might also result in significant perpetual cognitive deficits if the infant manages to survive. Microcephaly is caused by a number of variables, including chromosomal abnormalities as well as other genetic conditions, infections during pregnancy, for instance; rubella, toxoplasmosis, and prenatal exposure to dangerous toxicants.

Although drastically deficient cognitive growth is prevalent, problems with motor control processes not showing up until much later in life.  Most negatively impacted infants have severe neurological abnormalities and sometimes seizures, as well. Motor function and verbal advancement may also be deferred while hyperactivity and intellectual disability are both prevalent, however to varying degrees. Convulsions are also possible with variations in motor ability; from clumsiness to spastic quadriplegia in some people. The majority of cases of microcephaly are caused by genetic variations. On the one hand, linkage has been discovered between autism, gene duplications, and macrocephaly. On the contrary, a link has been discovered between schizophrenia, gene removals, and microcephaly. Several genotypes, termed as "MCPH" genes, after the gene microcephalin (MCPH1), because of their involvement in cranial capacity and primary microcephaly neuropathies when mutations occur. WDR62 (MCPH2), ASPM (MCPH5), CDK5RAP2 (MCPH3), CENPJ (MCPH6), KNL1 (MCPH4), STIL (MCPH7), CEP152 (MCPH9), ZNF335 (MCPH10), CEP135 (MCPH8), CDK6 (MCPH12), and PHC1 (MCPH11) are among the other genes related to microcephalin gene.  Furthermore, a link has been found among repeated genetic variations in recognised genes, including MCPH1 and CDK5RAP2 with structural variations of the brain as examined by Magnetic Resonance Imaging (MRI). The Centres for Disease Control and Prevention and the International Society for Infectious Diseases have linked the expansion of vector-borne Zika virus to an increase in genetically inherited microcephaly. Zika can be transmitted from a pregnant woman to her foetus.

Being caused by a reduction in cerebral cortex, and it can occur throughout embryonic and foetal growth phases because of inadequate neural stem cell advancement, impeded neurogenesis, or decrease of neural stem cells. Many genes needed for standard neural development have been discovered through studies in animal models such as rodents. The genes associated with the Notch pathway, for instance, govern stem cell advancement and neurogenesis. Genetic variations induced in mouse models in an experimental setting can induce microcephaly that in comparison is similar to that of the human beings. Abnormal Spindle-like Microcephaly-Associated (ASPM) gene abnormalities have been linked to human microcephaly, and a knockout-model of a ferret with extreme microcephaly has now been designed. Furthermore, viruses like Zika virus and Cytomegalovirus (CMV) have been found to afflict and destroy the brain's primary stem cells and radial glial cells, resulting in the destruction of daughter neurons.

A comprehensive physical and history assessments are carried out on patients with microcephaly. Neuroimaging, metabolic evaluation, and genetic examination should be taken into consideration in cases of deteriorating microcephaly. Neuroimaging with Magnetic Resonance Imaging (MRI) is mostly utilized as the very first diagnostic analysis in children suffering from microcephaly. Genetic screening is frequently the very next process after imaging techniques. Microcephaly is a long-term condition with no specific treatment available.