Septo-optic Dysplasia (de Morsier Syndrome)

Septo-optic dysplasia (SOD), also known as de Morsier syndrome, is a rare, congenital, and heterogeneous developmental anomaly.
The diagnosis is established clinically by the presence of any two of the following three classic features:
- midline forebrain defects (such as agenesis of the septum pellucidum and/or corpus callosum),
- optic nerve hypoplasia (ONH), and
- hypopituitarism secondary to hypothalamo-pituitary maldevelopment.
Approximately 30% of affected patients manifest the complete clinical triad, whereas roughly 60% have an absent septum pellucidum and 62% exhibit some degree of hypopituitarism.

Ophthalmologic Findings: Optic nerve hypoplasia may be unilateral or bilateral (bilateral is more common, accounting for 88% of cases) and frequently presents with nystagmus and visual impairment in early infancy.
Endocrine Dysfunction: The endocrinopathy typically evolves with a progressive loss of anterior and/or posterior pituitary function over time. Growth hormone (GH) deficiency is the most common endocrinopathy, causing a decrease in growth velocity. Deficiencies in adrenocorticotropic hormone (ACTH) and thyroid-stimulating hormone (TSH) are also frequent, potentially presenting as severe neonatal hypoglycemia. Central diabetes insipidus can also occur, presenting as polyuria and polydipsia.
Neurological and Systemic Findings: Neurological manifestations range from normal cognition to global developmental retardation, focal deficits, epilepsy, or hemiparesis. It may also be associated with midline facial anomalies, including cleft palate or a solitary median maxillary central incisor.

Neuroimaging: Magnetic Resonance Imaging (MRI) frequently demonstrates the classic triad of a small or hypoplastic anterior pituitary gland, an attenuated or absent pituitary stalk, and an ectopic posterior pituitary bright spot, alongside the absence of the septum pellucidum.
Genetics and Etiology: The etiology is multifactorial, involving both genetic and environmental components. While the majority of cases are sporadic, mutations in critical transcription factor genes involved in forebrain and pituitary development—specifically HESX1, SOX2, OTX2, and TCF7L1—have been identified in a small subset of patients. Environmental risk factors include viral infections, prenatal exposure to drugs or alcohol, and young maternal age.