disease has basis in disruption of disease caused by disruption of disease has major feature midbrain development Absent septum pellucidum septooptic dysplasia disorder of development or morphogenesis congenital absence of septum pellucidum https://github.com/monarch-initiative/mondo/issues/4069 https://rarediseases.info.nih.gov/diseases/9253/absence-of-septum-pellucidum UMLS:C0431371 ICD9:742.4 SCTID:253143001 MESH:C535562 MONDO:0022349 The absence of the septum pellucidum is a rare condition that affects the structure of the brain. Specifically, a thin membrane called the septum pellucidum is missing from its normal position in the middle of the brain. When it is missing, symptoms may include learning difficulties, behavioral changes, seizures, and changes in vision. Absence of the septum pellucidum is not typically seen as an isolated finding. Instead, absence of the septum pellucidum is associated with other conditions such as septo-optic dysplasia. Treatment options for the condition vary depending on the underlying disorder. Diagnosis of absence of the septum pellucidum can be made through imaging such as an MRI. Symptoms of absence of the septum pellucidum typically present during childhood, but a diagnosis can also be made before an individual is born (prenatally). If an individual is found to be missing the septum pellucidum, a search for an underlying disorder should be made. MEDGEN:96561 GARD:0009253 absence of septum pellucidum Editor note: consider representing as finding