Prenatally diagnosed developmental abnormalities of the central nervous system and genetic syndromes: A practical review

Developmental brain abnormalities are complex and can be difficult to diagnose by prenatal imaging because of the ongoing growth and development of the brain throughout pregnancy and the limitations of ultrasound, often requiring fetal magnetic resonance imaging as an additional tool. As for all major structural congenital anomalies, amniocentesis with chromosomal microarray and a karyotype is the first-line recommended test for the genetic work-up of prenatally diagnosed central nervous system (CNS) abnormalities. Many CNS defects, especially neuronal migration defects affecting the cerebral and cerebellar cortex, are caused by single-gene mutations in a large number of different genes. Early data suggest that prenatal diagnostic exome sequencing for fetal CNS defects will have a high diagnostic yield, but interpretation of sequencing results can be complex. Yet a genetic diagnosis is important for prognosis prediction and recurrence risk counseling. The evaluation and management of such patients is best done in a multidisciplinary team approach. Here, we review general principles of the genetic work-up for fetuses with CNS defects and review categories of genetic causes of prenatally diagnosed CNS phenotypes.