A neurodevelopment disorder
Microcephaly is a crude label for something that goes wrong during the growth of a foetus which results in a deformity or a failure of the babies head and brain to fully develop.
Because it is something relatively rare and little known the level of understanding is minimal and medical specialists are really best guessing.
The affected newborns generally have a smaller than normal head, possibly symptoms of dwarfism and as they grow they will exhibit neurological defects with severely impaired intellectual development although some impairments may not be apparent until the child is older and attempts to become socialised.
Typically with such children, intellectual disability, impaired motor skills (clumsiness), spasticity and other symptoms have been reported. But even if the affected child acquires normal physical and communication skills, and they will find it very difficult to socialise.
In general, life expectancy for individuals with microcephaly is reduced and the prognosis for normal brain function is poor. The prognosis varies depending on the presence of other associated abnormalities
The 2016 outbreak of microcephaly was initially associated with the spread of zika virus, however many medical professionals consider that a more probable cause was agricultural chemicals and pesticides.