Herpes Simplex
Congenital microcephaly can occur due to transplacental transmission of herpes simplex early during pregnancy. Neonates with congenital herpes simplex infection tend to be premature and often have chorioretinitis, microphthalmia, multicystic encephalomalacia, and cerebral calcifications. The diagnosis may be established by specific detection of viral DNA or by IgM-enzyme-linked immunosorbent assay. Viral DNA detection techniques using polymerase chain reaction to amplify small amounts of DNA has improved the accuracy of viral DNA detection. Viral DNA detection is more reliable than IgM-enzyme-linked inmunosorbent assay because early infection may not produce an IgM reaction.

Autosomal Dominant Microcephaly
Neonates with autosomal dominant microcephaly have features that are not distinct enough to be considered dysmorphic, yet some of these neonates have upslanting palpebral fissures, slanting forehead, and prominent ears. Pathological studies have not been reported in patients with autosomal dominant microcephaly. The diagnosis is established by measuring the head circumference of the parents and finding that one of them is microcephalic.