Septo-optic dysplasia (SOD) is the commonest of the midline cerebral/cranial abnormalities involving the spectrum of holoprosencephaly, absence of the corpus callosum (see entry, Agenesis of the Corpus Callosum) and midline cleft palate and also involving the hypothalamopituitary region. It comprises two out of the three features of optic nerve hypoplasia (ONH) unilateral or bilateral, absence of the septum pellucidum and pituitary dysfunction. Because fifty per cent of patients with this condition have a septum pellucidum present, the older name of De Morsier's syndrome may be preferable. The loss of vision is extremely variable. Although the optic nerve and cerebral abnormalities are fixed, the pituitary dysfunction (see entry, Pituitary Disorders) is often variable and may well evolve with time. It also has the unusual characteristic of being commonly associated with diabetes insipidus, as well as anterior pituitary dysfunction. The anterior pituitary function commonly evolves with time and may well also be associated with retention of gonadotrophin secretion with either normal or precocious puberty (see entry, Premature Sexual Maturation)

All children with midline cerebral or cranial abnormalities should be seen by an endocrinologist. Epilepsy in such children is often due to the endocrinopathy (abnormal plasma sodium concentration in diabetes insipidus and hypoglycaemia associated with growth hormone deficiency and/or cortisol deficiency) rather than due to the structural brain abnormality.

Since SOD can be highly variable in terms of its endocrine phenotype, with the possibility of evolution of other hormonal deficiencies over time, a child with the condition needs to be carefully evaluated with close monitoring and follow up. In particular, cortisol deficiency is not always easy to diagnose, and a careful evaluation of the hypothalamo-pituitary-adrenal axis is mandatory, as missing the diagnosis may lead to hypoglycaemia particularly at times of intercurrent illness. Other features of SOD include obesity, behavioural and learning difficulties, and sleep disorders.

Inheritance patterns
Septo-optic dysplasia is largely thought to be a sporadic disorder. However, in the light of the recent identification of the HESXI gene, it is now clear that genetic mutations in this gene may account for some cases of SOD. Additionally, there is increasing evidence to suggest that septo-optic dysplasia is a multigenic disorder, with other genes being involved, and possible interaction with environmental factors, ultimately leading to a phenotype.

Prenatal diagnosis
At present, this is only available for those rare families with an autosomal recessive form of SOD due to HEXSI mutations.

Medical text written October 2001 by Dr R Stanhope and Dr M Dattani. Last updated September 2005 by Dr R Stanhope, Consultant Paediatric Endocrinologist, Great Ormond Street Hospital, London, UK and Dr M Dattani, Reader and Hon. Consultant in Paediatric Endocrinology, Institute of Child Health, London, UK.

Further Online Resources
Medical texts in The Contact a Family Directory are designed to give a short, clear description of specific conditions and rare disorders. More extensive information on this condition can be found on a range of reliable, validated web sites and links to them are included in the CD-ROM version of this Directory. Further information on these resources can be found in our Medical Information on the Internet article.

SOD/ONH SUPPORT NETWORK

SOD/ONH Support Network
Corpus Christi Barge
Meadow Lane
Oxford
OX4 4BJ
Tel: 07930 627 144
e-mail: arvatec@tesco.net
Web: http://www.focusfamilies.org

The Network is a family support network, established in 2000. It offers support for families and linking where possible. It publishes a newsletter and has information available, details on request. The Network has over 50 UK families in membership. Over 300 families world wide link through Focus Families which has groups in Australia, Canada, the USA as well as in the UK.

Group details last updated February 2008.