Septo-optic dysplasia (De Morsier syndrome) is a developmental anomaly of 
mid-line brain structures and includes optic nerve hypoplasia, absence of the 
septum pellucidum and hypothalamo-pituitary abnormalities. We describe seven 
patients (four female, three male) who had at least two out of the three 
features necessary for the diagnosis of septo-optic dysplasia. Four patients had 
hypopituitarism and yet normal gonadotrophin secretion: one of these also had 
anti-diuretic hormone insufficiency; three had isolated GH deficiency and yet 
had premature puberty, with the onset of puberty at least a year earlier than 
would have been expected for their bone age. In any progressive and evolving 
anterior pituitary lesion it is extremely unusual to lose 
corticotrophin-releasing hormone/ACTH and TRH/TSH secretion and yet to retain 
gonadotrophin secretion. GnRH neurons develop in the nasal mucosa and migrate to 
the hypothalamus in early fetal life. We hypothesise that the arrival of GnRH 
neurons in the hypothalamus after the development of a midline hypothalamic 
defect may explain these phenomena. Progress in spontaneous/premature puberty in 
children with De Morsier syndrome may have important implications for 
management. The combination of GH deficiency and premature puberty may allow an 
apparently normal growth rate but with an inappropriately advanced bone age 
resulting in impaired final stature. GnRH analogues may be a therapeutic option. 
In conclusion, some patients with De Morsier syndrome appear to retain the 
ability to secrete gonadotrophins in the face of loss of other hypothalamic 
releasing factors. The migration of GnRH neurons after the development of the 
midline defect may be an explanation.