Neurodevelopmental disorder where a child's skull growth fails to keep up with the rest of the skeleton, with many different causes.Encyclopedia Entry for Microcephaly :Microcephaly. Microcephaly most often occurs because the brain does not grow at a normal rate. The growth of the skull is determined by brain growth. Brain growth takes place while a baby is in the womb and during infancy. Conditions that affect brain growth can cause smaller than normal head size. These include infections, genetic disorders, and severe malnutrition. Genetic conditions that cause microcephaly include: Cornelia de Lange syndrome Cri du chat syndrome Down syndrome Rubinstein-Taybi syndrome Seckel syndrome Smith-Lemli-Opitz syndrome Trisomy 18 Trisomy 21 Other problems that may lead to microcephaly include: Uncontrolled phenylketonuria (PKU) in the mother Methylmercury poisoning Congenital rubella Congenital toxoplasmosis Congenital cytomegalovirus (CMV) Use of certain drugs during pregnancy, especially alcohol and phenytoin Becoming infected with the Zika virus while pregnant can also cause microcephaly. The Zika virus is present in Brazil and other parts of South America, along with Mexico, Central America, and the Caribbean.Most often, microcephaly is diagnosed at birth or during routine well-baby exams. Talk to your health care provider if you think your infant's head size is too small or not growing normally. Call your provider if you or your partner has been to an area where Zika is present and you are pregnant or thinking about becoming pregnant.Most of the time, microcephaly is discovered during a routine exam. Head measurements are part of all well-baby exams for the first 18 months. Tests take only a few seconds while the measuring tape is placed around the infant's head. The provider will keep a record over time to determine: What is the head circumference? Is the head growing at a slower rate than the body? What other symptoms are there? It may also be helpful to keep your own records of your baby's growth. Talk to your provider if you notice that the baby's head growth seems to be slowing down. If your provider diagnoses your child with microcephaly, you should note it in your child's personal medical records.Skull of a newborn Skull of a newborn Microcephaly Microcephaly Ultrasound, normal fetus - ventricles of brain Ultrasound, normal fetus - ventricles of brain.Centers for Disease Control and Prevention website. Zika virus. www.cdc.gov/zika/index.html. Updated November 9, 2017. Accessed November 12, 2017. Johansson MA, Mier-Y-Teran-Romero L, Reefhuis J, Gilboa SM, Hills SL. Zika and the risk of microcephaly. N Engl J Med. 2016;375(1):1-4. PMID: 27222919 www.ncbi.nlm.nih.gov/pubmed/27222919. Kinsman SL, Johnston MV. Congenital anomalies of the central nervous system.