Septo-optic dysplasia

Overview
Septo-optic dysplasia (SOD) (de Morsier syndrome) is a congenital malformation syndrome manifested by hypoplasia (underdevelopment) of the optic nerve, hypopituitarism, and absence of the septum pellucidum (a midline part of the brain). In a severe case, this results in pituitary hormone deficiencies, blindness, and mental retardation. However, there are milder degrees of each of the three problems, and some children only have one or two of the three.

Neuroradiologically, intracranial malformations associated with septo-optic dysplasia include agenesis of the corpus callosum, schizencephaly, and lobar holoprosencephaly.

Optic nerve
The optic nerve hypoplasia is generally manifested by nystagmus (involuntary eye movements, often side-to-side) and a smaller-than-usual optic disk. The degree of visual impairment is variable, and ranges from normal vision to complete blindness. When nystagmus develops, it typically appears by 1-4 months of age, and usually indicates that there will be a significant degree of visual impairment, but the severity is difficult to predict in infancy. Although there are many measures to compensate for visual impairment, no treatment is available to induce normal optic nerve function.

Pituitary
The degree of pituitary deficiency is also variable, and ranges from normal function, to deficiency of a single hormone, to deficiency of both anterior and posterior hormones. It is often unclear if the hypopituitarism is due to a primary pituitary dysfunction or is secondary to a hypothalmic dysfunction. Hypopituitarism in this syndrome is most often manifested by growth hormone deficiency. If severe, it can lead to diagnosis in the first days of life by causing hypoglycemia, jaundice, and micropenis (if a boy). The cause of the jaundice is unknown, and an unusual aspect of it (compared to most neonatal jaundice) is that it can be largely a conjugated (direct) hyperbilirubinemia suggestive of obstructive liver disease. It typically resolves over several weeks once hormone replacement is begun. All of the pituitary hormones can be replaced, and this is the treatment for deficiencies. Septo-optic dysplasia is one of the most common forms of congenital growth hormone deficiency.

Septum pellucidum
The brain effects are also variable and range from normal intelligence to severe mental retardation. Seizures sometimes occur. Prediction of intellectual outcome in infancy is difficult. Various types of early intervention or equivalent programs can help a child reach full developmental potential, but if brain impairment is significant, it cannot be made normal by any treatment.

Variability
Septo-optic dysplasia is a highly variable disorder. It is rare for siblings to present with identical features of the Septo-optic dysplasia spectrum. Many patients present with additional developmental defects outside the Septo-optic dysplasia triad. In particular digital defects are common.

Causes
Septo-optic dysplasia is a developmental disorder resulting from a defect of normal embryological development. The cause of septo-optic dysplasia is not known. Rare familial recurrence has been reported, suggesting at least one genetic form (HESX1), but in most cases it is a sporadic birth defect of unknown cause and does not recur again with subsequent pregnancies.

Septo-optic dysplasia is linked to young maternal age. Indeed one third of Septo-optic births are the result of teenage pregnancies. These data could support an environmental origin of SOD with possible exposure to risk factors such as maternal smoking, alcohol consumption, and use of addictive drugs during early gestation. However, young maternal age in SOD was not associated with low birth weight or low gestation. This lack of association between young maternal age and an adverse developmental environment, as indicated by birth weight and gestation, suggest that maternal factors such as maternal smoking, alcohol consumption, and use of addictive drugs during early gestation are not a cause of Septo-optic dysplasia.