Absence of the Septum Pellucidum

What Causes Absence of the Septum Pellucidum?

ASP has many different possible causes, and it is usually associated with an underlying condition that causes abnormal development of more than one part of the brain.

Conditions that may be associated with ASP include:

• Agenesis of the corpus callosum (ACC) is a brain disorder where the structure connecting the two sides of the brain, the corpus callosum, is either partially or entirely missing. When the corpus callosum is missing, the septum pellucidum is also absent. The corpus callosum enables communication between the left and right cerebral hemispheres of the brain. When it is missing, normal communication between the two halves of the brain is not possible. Neurological and developmental symptoms can result.
• Septo-optic dysplasia (SOD) is characterized by the abnormal development of parts of the brain and nervous system. It occurs during fetal development and is present at birth. Symptoms of the disorder vary widely and may include blindness, hormonal problems, and intellectual disabilities.

Other disorders sometimes associated with ASP include:

• Arnold-Chiari malformation
• Dandy-Walker syndrome
• Schizencephaly (abnormal divisions in the brain)
• Holoprosencephaly (lack of normal separation of the brain’s hemispheres)
• Aicardi syndrome
• Hydrocephalus (accumulation of fluid inside the brain, which may cause degeneration of the septum pellucidum)

Is Absence of the Septum Pellucidum Hereditary?

Many of the conditions associated with ASP may be inherited. However, the pattern of inheritance, along with the risk of a parent passing the disorder-causing genes to their children, varies depending on the underlying condition.

In some cases, agenesis of the corpus callosum may be inherited in either an autosomal recessive or X-linked dominant pattern. In an X-linked dominant pattern, the disease-causing mutation is on the X chromosome, and only one copy of the mutation is necessary to cause the disorder. Females have two X chromosomes and will develop the condition if one of the chromosomes carries the mutation. Males have only one X-chromosome and will develop a more severe form of the disorder if their X chromosome carries the mutation. Often, the condition is fatal to males during pregnancy. The result is that this form of the condition is more common in females. This is the case with ACC associated with Aicardi syndrome.

Most children born with septo-optic dysplasia do not have a family history of the disease, and parents who have one child with SOD do not seem to be more likely to have another child with the disorder. However, a small number of cases have occurred in multiple members of the same family. In most cases, the mutations associated with SOD appear to be inherited in an autosomal recessive pattern. SOD also seems to have been inherited in an autosomal dominant pattern in a small number of inherited cases. In these cases, the disorder develops if the child inherits even one copy of the mutated gene

How Is Absence of the Septum Pellucidum Detected?

Early treatment of the symptoms associated with ASP, especially those such as the hormonal deficiencies of SOD, can significantly improve outcomes in the future.

Sometimes, signs of ASP are apparent in ultrasound exams during pregnancy. However, the condition may go unnoticed until some time after birth. Seizures are the most common symptom that will lead a doctor to suspect ASP or ACC in an infant or young child, but not all children with these conditions experience seizures.

Other early signs of ASP can include:

• Feeding difficulties
• Problems holding the head upright
• Delays in motor skills such as sitting, crawling, or walking
• Other cognitive, intellectual, or motor delays
• Accumulation of fluid around the brain (hydrocephalus)
• Vision impairment
• Involuntary eye movements
• Slow growth
• Lethargy
• Low blood sugar in early childhood
• Excessive thirst
• Seizures

How Is Absence of the Septum Pellucidum Diagnosed?

A doctor may suspect ASP if a child presents symptoms of the disorder with no other apparent cause, especially if there are risk factors such as a family history of associated conditions. Doctors may also recommend diagnostic testing if they observe signs of ASP in routine ultrasound exams during pregnancy. When ASP is identified, doctors will conduct further testing to locate the condition’s underlying cause.

Diagnostic steps may include:

• High-resolution ultrasound exams that provide more detail than routine ultrasound
• Magnetic resonance imaging (MRI) either during pregnancy or after birth to confirm ACC and look for other abnormalities
• Genetic testing during pregnancy via amniocentesis

PLEASE CONSULT A PHYSICIAN FOR MORE INFORMATION.

How Is Absence of the Septum Pellucidum Treated?

ASP has no cure, and there is no way to correct the absence of the septum pellucidum. Treatments for the disorder focus on controlling symptoms, and treatment programs vary depending on the underlying cause and the specific symptoms present. In mild cases of ACC that produce no significant symptoms, no treatment may be necessary.

Treatment for ASP and associated disorders may include:

• Anti-seizure medications
• Physical therapy
• Speech therapy
• Occupational therapy
• Surgery to control hydrocephalus
• Hormone replacement therapy
• Vision therapies

How Does Absence of the Septum Pellucidum Progress?

ASP is not a progressive disorder. The structural brain abnormalities don’t worsen over time. However, some symptoms and complications of the associated underlying conditions may not emerge until later in childhood.

Possible long-term complications of ACC include:

• Seizures
• Speech difficulties
• Intellectual impairment
• Headaches
• Poor coordination
• Impaired vision
• Impaired hearing
• Obesity
• Sexual development problems

How Is Absence of the Septum Pellucidum Prevented?

People who have a family history of disorders associated with ASP may want to seek the advice of a genetic counselor if they are planning to have children.

Several factors have been associated with increased risk of disorders often related to ASP. Risk factors to avoid include:

• Excessive alcohol consumption during pregnancy
• Exposure to drugs and toxins during pregnancy
• Smoking or alcohol use during pregnancy
• Viral infections during pregnancy
• Pregnancy at a young age
• Exposure to some medications (including some anticonvulsants and quinine)

Absence of the Septum Pellucidum Caregiver Tips

• Learn as much as you can about the disorder underlying your child’s ASP. Most of these disorders are rare and highly variable, so your child’s experience is going to be unlike that of any other child with ASP. The more you know about the condition, the better able you’ll be to help your child deal with the impacts of ASP.  The Child Neurology Foundation provides access to a peer support network to assist families living with neurological disorders such as ACC.
• If your child has SOD, get support from others who know what it’s like to live with the disorder. The MAGIC Foundation maintains resources, including links to online support groups, for families living with SOD and optic nerve hypoplasia.

Absence of the Septum Pellucidum Brain Science

The septum pellucidum (SP) is a thin membrane deep in the middle of the brain between the left and right hemispheres of the brain’s cerebral cortex. The SP is connected to a layer of nerve cells called the corpus callosum. The corpus callosum is made up of nerve fibers that span the divide between the hemispheres. The absence of the SP is often associated with corresponding underdevelopment or absence of the corpus callosum (ACC).

The function of the corpus callosum is to transmit nerve signals from one hemisphere to the other. This function comes into play when, for example, sensory input is delivered to one hemisphere and then is passed to the other hemisphere for processing. When the corpus callosum is absent, this kind of cross-hemisphere processing is not possible.

Scientists have discovered that many brain functions work just fine even without communication between the cerebral hemispheres. This may explain why some people with ACC experience mild symptoms or none at all. However, some functions, such as language processing, rely on collaboration between the hemispheres. For example, studies of people without a functional corpus callosum found that when they were shown an object visible to them only through their left eye, they could not think of the object’s name. The researchers hypothesized that the right cerebral hemisphere received the sensory input from the left eye as it usually does. But the sensory data couldn’t be sent to the left hemisphere, where the brain’s language-processing center is located.

Absence of the Septum Pellucidum Research

Title:  Brain Development Research Program

Stage: Not yet recruiting

Principal investigator: Elliott H. Sherr, MD, PhD

University of California, San Francisco

San Francisco, CA

Dr. Elliott Sherr and his collaborators at the University of California, San Francisco (UCSF) are studying the genetic causes of disorders of cognition and epilepsy, in particular disorders of brain development that affect the corpus callosum, such as Aicardi syndrome, as well as two additional brain malformations, polymicrogyria and Dandy-Walker malformation. The investigators’ research aims to use a better understanding of the underlying genetic causes as a foundation to develop better treatments for these groups of patients.

They are studying both the genetics and clinical features of these disorders. They hope to understand the problems faced by individuals with these disorders as well as their causes. In the future, we hope to develop therapies that are geared specifically for individuals based on the underlying biology. To participate in the study, participants will be asked to provide a copy of the magnetic resonance imaging (MRI) documenting Agenesis Corpus Callosum (ACC), Polymicrogyria (PMG), or Dandy-Walker malformation (DWM), clinical information, and saliva or blood samples from the affected individual and the parents. Please see contact information and our webpage below.

Title: Study of Selected X-Linked Disorders: Aicardi Syndrome

Stage: Recruiting

Principal investigator: Ignatia B. Van den Veyver, MD

Baylor College of Medicine

Houston, TX

Aicardi syndrome is a sporadic X-linked dominant, presumably male-lethal, neurodevelopmental disorder. It was initially characterized by agenesis of the corpus callosum, neuronal migration defects, eye abnormalities (chorioretinal lacunae, colobomas of the optic nerve, and microphthalmia), and severe early-onset seizures and neurodevelopmental delay. It is now well recognized that other brain abnormalities, such as polymicrogyria, agyria, cysts, and heterotopias, are common features of Aicardi syndrome. We previously hypothesized that the gene causing Aicardi syndrome and possibly other phenotypically similar disorders with X-linked inheritance, such as Goltz syndrome or Focal Dermal Hypoplasia, are in or near the region on chromosome Xp22 that is deleted in another condition named microphthalmia with linear skin defects syndrome (MLS) because all three have some clinical similarities. However, interim studies have shown that this is likely not the case because no mutations were found in Aicardi syndrome in human holocytochrome c-type synthetase (HCCS), the deleted or mutated gene in MLS. In addition, a mouse model for MLS has no features of Aicardi syndrome. Furthermore, we identified mutations in PORCN (Xp11.3) in Goltz syndrome patients but not in Aicardi syndrome patients. Therefore, it is likely that the mutated gene is elsewhere on the X-chromosome.

For this study, they are collecting information on patients with clinical findings suggesting a diagnosis of Aicardi syndrome, MLS syndrome, or a condition that phenotypically overlaps with these disorders. When indicated, a detailed family history will be obtained, and additional family members will be evaluated after appropriately obtained written voluntary consent. A detailed report of the history or physical findings will be obtained from referring physicians for patients identified at outside facilities, or the study collaborators may evaluate the participants. Blood and skin biopsy will be obtained from affected individuals, unaffected parents, and from other affected or unaffected family members where indicated. It is anticipated that some severely affected patients will expire; in that case, (post mortem) pathological specimens may be obtained. Occasionally, affected individuals may undergo surgical procedures to remove tissues; in this case, researchers may obtain tissues that would be otherwise discarded or that are not essential for further diagnostic studies or clinical care of the patient. It is anticipated that these specimens will be extremely valuable for understanding the pathogenesis of the investigated conditions. DNA, RNA, or protein will be prepared from leukocytes and tissues and used for mutation analysis and other molecular studies of the identified genes. Permanent lymphoblastoid cell lines will be prepared and stored in the laboratory as a permanent source of DNA for molecular studies.

Title: Human Epilepsy Genetics–Neuronal Migration Disorders Study

Stage: Recruiting

Contact: Christopher A. Walsh, MD, PhD

Boston Children’s Hospital

Boston, MA

Epilepsy is responsible for tremendous long-term healthcare costs. Analysis of inherited epilepsy conditions has allowed for identifying several key genes active in the developing brain. Although many genetic abnormalities of the brain are rare and lethal, rapidly advancing knowledge of the structure of the human genome makes it a realistic goal to identify genes responsible for several other epileptic conditions.

This study aims to identify genes responsible for epilepsy and disorders of human cognition (EDHC). The Walsh Laboratory at the Children’s Hospital Boston and Beth Israel Deaconess Medical Center is looking for genes involved in brain development. Conditions that we study include brain malformations, such as polymicrogyria, lissencephaly, Walker-Warburg syndrome, heterotopias, cerebellar hypoplasia, and inherited disorders of cognition, such as familial mental retardation and familial autism; people with these conditions also often have epilepsy. The structural brain abnormalities are usually diagnosed by brain MRI or sometimes CT scans. Adults and children with these conditions, and their family members, are invited to participate in our study. By comparing the DNA of individuals or families that carry EDHC to the DNA of people in the general population, it may be possible to learn more about the genetic bases of certain forms of EDHC.

Study participants must have a brain malformation or disorder of cognition such as mental retardation or autism in addition to epilepsy to take part in this research.