What Is Septo-Optic Dysplasia

Introduction

Septo-Optic Dysplasia (SOD) is a diagnosis typically given to children who have optic nerve hypoplasia, a condition described by abnormalities in the midline of the brain and dysfunctions in the pituitary gland. Previously known as de Morsier syndrome, this condition is congenital, which means that it is present at birth. It is a very rare disorder that does not become apparent until childhood, with some cases being diagnosed as late as adolescence.¹ While the exact causes of SOD remain unknown, it is thought to result from a complex interplay of genetic and environmental factors. Genetic research has identified specific mutations in genes such as HESX1, OTX2 and SOX2 that play a crucial part in the development of the pituitary gland and optic nerves. While there is no cure for this condition, there is a variety of available resources that can help address and manage the symptoms. The severity of the symptoms the patients can present with can vary hugely between children, which is why SOD management is not considered to be “one size fits all”. This article delves into the clinical presentation, diagnosis, management and prognosis of SOD, shedding light on a condition that often remains in the shadows of medical understanding.

Background information

As mentioned in the introduction, SOD is a very rare condition, with a reported incidence rate of 1 in 10,000 newborns. SOD has a sporadic occurrence and can occur in families that have no previous history of the disorder. In some rare cases, SOD incidence has been shown to run in families, suggesting that there are genetic forms of the disorder. While this is not a largely accepted theory of causation, there is ongoing research into the genetic background of the disorder, with new variants such as the SOX2 gene still being discovered today.¹ In particular, three genes (HESX1, OTX2 and SOX2) have all been associated with SOD. Importantly, these genes are implicated in the formation of the pituitary gland, the eyes and structures associated with the optic nerves.³ The inheritance of the disease is autosomal recessive, meaning that two copies of the mutated gene are required to cause the disorder (one from each parent), however, less than 1% of children receive a genetic diagnosis due to its rarity.⁴  

Currently, there is no single known cause of SOD but it is thought that a combination of genetic and environmental factors can play a part in the development of the condition. The environmental factors that can increase the risk of giving birth to a child with SOD include: 

• The age of the parents
  • Some epidemiology research suggests that younger mothers were at a significantly greater risk of giving birth to a child with SOD, particularly in the UK.⁵ 
• The number of times the mother has previously given birth 
• Substance abuse 
• Alcohol and smoking 
• Antenatal (during pregnancy) bleeding 
• Ethnicity⁴ 

Clinical presentation

The clinical presentation of the disorder involves three components: ocular (visual) abnormalities, dysfunction in the pituitary glands, and neurological delays. Only one-third of the children diagnosed with SOD will present with all three features.²

Ocular abnormalities

• Optic Nerve Hypoplasia - due to the abnormal development of the brain's hemispheres in SOD, the nerves connected to the eyes can become damaged.⁶ 

• Due to the underdevelopment of the optic nerves, the child can experience visual impairments and disturbances. It can cause mild to severe blindness, and also an uncontrollable shaking of the eyes, a condition known as nystagmus. These conditions can occur either in one eye or both. While these are early occurrences, strabismus, a condition where the eyes may not properly align when looking at objects and people, can develop up to a year later.⁷

Hypopituitarism

• Growth Hormone Deficiency (GHD) - The underdevelopment of the pituitary gland in this disorder causes this structure to secrete at levels lower than normal.. The most common form of hypopituitarism in SOD comes in the form of growth hormone deficiencies.⁸ Children with GHD tend to be shorter than most of the children their age, although the proportions of their bodies remain the same.⁹ 

• Thyroid Dysfunction - hypopituitarism can also lead to the abnormal functioning of the thyroid, due to a lack of hormones produced by the pituitary gland that is normally needed for the thyroid to work properly. An underactive thyroid can lead to symptoms such as weight gain, fatigue, and feelings of low mood.¹⁰ 

• Adrenal Insufficiency - in very rare and serious cases, the lack of a hormone that controls cortisol levels can cause an adrenal crisis. This crisis presents as a range of symptoms including nausea, fatigue, and low blood sugar levels. Specifically, the most common sign is prolonged jaundice in newborn babies. Adrenal insufficiency is a life-threatening occurrence, however, with immediate medical attention it can be treated.¹¹ 

Neurological abnormalities

Neurological symptoms of SOD typically develop later on in the condition. They result from structures located in the middle of the brain not developing properly, leading to the following abnormalities:⁸

• Intellectual and developmental delays - studies have shown that intellectual disability occurs in 71% of SOD cases.¹² Intellectual and developmental delay means that children with SOD can take longer to reach certain developmental milestones than other children their age. This typically affects practical, social, and motor skills.¹³ 

• Seizures - in some rare cases, children with SOD can present with early signs of epilepsy, where they may experience recurring seizures.¹⁴  

• Cerebral Palsy - This is the most common motor disability seen in children as a whole, and can affect movement and coordination.¹⁵ It is estimated that 57% of SOD cases show symptoms of cerebral palsy.¹² 

• Behavioural Issues - it is thought that 20% of SOD cases present with behavioural issues, with symptoms similar to the ones observed in individuals with autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD).¹⁶ 

Diagnosis

The method for diagnosing SOD is done by using a neuroimaging method known as a magnetic resonance imaging (MRI) scan. This imaging technique is useful when looking at the abnormalities in the midline of the brain, including the absence of the septum pellucidum.¹⁷ When looking at the scans, the abnormalities that can be seen in the hemispheres of the brain can predict the severity of the neurodevelopmental deficits the child will experience. Adding to this, the scan can show any abnormalities associated with the pituitary gland, which can also provide information about the hormonal deficiencies that come with SOD¹⁸. 

Recently, clinicians have been increasingly using fetal ultrasonography, a technique that can detect the missing septum pellucidum and other key components of SOD, such as large ventricles. This can then be followed up using fetal MRI that can help to detect the malformations early on during pregnancy.¹⁹ Research has shown that abnormalities associated with SOD develop in the embryonic forebrain between the first 4-6 weeks of pregnancy.⁸ Early diagnosis of this disorder can help to improve the prognosis and severity of the condition, particularly with regarding to the hormonal deficiencies.

As well as imaging, other tests are carried out to account for the visual and hormonal symptoms of SOD. Blood tests are used to measure the hormone levels of the child, and vision tests are used to determine the severity of the disruption to the optic nerves.¹ 

Management and treatment

Currently there is no cure for SOD. On the other hand, the treatment routes aim to manage the symptoms of the disorder through hormone treatments and various types of therapy. This is usually done with a multidisciplinary team of neurologists, ophthalmologists and endocrinologists which target the neurodevelopmental deficits, vision issues and hormone imbalances, respectively. Some of the front-line treatments include: 

• Pituitary Hormone Replacement - Hormone replacement therapy helps to address the imbalance of hormones created by the dysfunctional pituitary gland. This treatment aims to identify absent or underproduced hormones and replace them to a normal functioning level, using artificially created hormones.²⁰ 

• Speech, occupational, or physical therapy - depending on the child’s individual needs there is a range of therapies that can help to address the developmental issues associated with SOD. These therapies can improve speech and communication skills, help to teach independent living to individuals, and also work with them to assist them in building muscle strength and developing motor skills for more efficient mobility.²¹ 

• Occlusion therapy - in some cases, the visual impairments can improve after the first several months of life, however, children may benefit from occlusion therapy if they suffer from optic nerve damage in one or both eyes. This treatment aims to encourage development in the eye with poorer vision, through wearing an eye patch on the healthier eye.²² 

Prevention and prognosis

There is no way to prevent SOD development. However, by avoiding several environmental factors during pregnancy can help to lower the risk. Adding to this, early diagnosis can help to reduce the symptoms caused by hormonal deficiencies, as hormone replacement therapies can be started early and are therefore given adequate time to work. The prognosis of the condition itself varies widely between patients. Some can present with severe learning disabilities and others may display neurotypical intelligence. Importantly, if the child requires medication for hormone replacement, lifelong treatment and follow-up is typically needed to manage the condition.²³ 

Summary

To summarize, SOD is a medical rarity that presents complex challenges for affected individuals and their families. Understanding this condition with its multifaceted clinical presentations and the latest diagnostic and management approaches is crucial. While SOD cannot be prevented, early diagnosis and intervention hold the potential to significantly improve the quality of life for those living with the disorder. With the ongoing research into the genetic basis of SOD and the advancements in medical therapies, there is hope for better outcomes and more personalised treatments for affected individuals. As we continue to explore the world of rare medical conditions, SOD serves as a reminder of the importance of medical research, early diagnosis and multidisciplinary approaches, to care in the mission of improving the lives of those affected.