Disorders of the Developing Nervous System

Abstract

In spite of the immense complexity, most infants are born with a normal nervous system containing 50–100 billion functioning nerve cells. Unfortunately, 1–2 % of infants are born with major neurodevelopmental defects. Forty percent of defects occur from genetic mutations, exposure to toxins or teratogens, central nervous system infections, metabolic deficiencies, and trauma. The importance of the timing of the defect onset in gestation is discussed. Types of defects, dysplasia, heterotopia, hamartoma, and malformation are covered. The chapter then discusses the specific birth defects of anencephaly, Chiari syndrome, phenylketonuria (PKU), Tay–Sachs disease, Down syndrome, and the spectrum of cerebral palsy. Attention is given to their pathophysiology, major clinical features, major laboratory findings, and principles of management and prognosis.

A nine- month-old infant is referred to a child neurologist for evaluation after her pediatrician noted that the baby was not meeting developmental milestones . The baby was born at term with no complications and had a normal neonatal period. The baby was noted at three months to be “floppy” or hypotonic, and the neurologist also noted an exaggerated startle to auditory stimuli. Fundoscopic examination revealed a bright red fovea surrounded by a dull whitish retina (cherry red spot). This constellation of symptoms and signs was concerning for Tay–Sachs disease and a confirmatory blood test showed deficient levels of hexosamindase A enzyme. The child went on to develop seizures, lose vision, and regress developmentally. Death occurred at 3 years.