Epilepsy-intellectual disability in females also known as PCDH19 gene-related epilepsy or epileptic encephalopathy, early infantile, 9 (EIEE9), is a rare type of epilepsy that affects predominantly females and is characterized by clusters of brief seizures, which start in infancy or early childhood, and is occasionally accompanied by varying degrees of cognitive impairment. The striking pattern of onset seizures at a young age, genetic testing and laboratory results, potential developmental delays or developmental regression and associated disorders, eases diagnosis.
The National Institutes of Health Office and Rare Disease Research characterizes PCDH19 gene-related epilepsy as a rare disorder. Although formal epidemiologic data is not available, results from diagnostic screenings indicate that approximately 1 out of 10 girls who have seizure onset before five years of age may have PCDH19 mutations.
Signs and symptoms PCDH19 gene-related epilepsy is a highly variable and rare epileptic syndrome, characterized by the early-onset of seizure clusters, with a range of 4–60 months, and an average onset at 12.9 months. Other aspects, such as varying degrees of cognitive impairment and behavioral and psychiatric problems, are also common, but are not essential for diagnosis of PCDH19 gene-related epilepsy.
PCDH19 gene-related epilepsy shares several clinical features with other early-onset epileptic encephalopathies, such as Dravet syndrome, generalized epilepsy with febrile seizures plus (GEFS+), FIRES (febrile infection–related epilepsy syndrome) Lennox–Gastaut syndrome or epilepsy of unknown origin. However, the disorder has a distinct evolution of symptoms, and is associated with specific genetic mutations of the PCDH19 gene.
Seizures The hallmark characteristic of PCDH19 gene-related epilepsy is early-onset cluster seizures that often cause cyanotic spells, which start in infancy or early childhood. The onset of the first cluster of seizures usually coincides with a fever (febrile seizures), however subsequent seizures may be febrile or afebrile. The seizure clusters are generally brief seizures, lasting 1–5 minutes, often accompanied by fearful screaming observed in 63% of girls. These cluster seizures can occur more than 10 times a day over several days, with varying amounts of time between seizure clusters.
Over time, children with PCDH19 gene-related epilepsy tend to exhibit multiple seizure types, including focal, generalized tonic-clonic, tonic, atonic, myoclonus, and absence seizures. In a small study of 35 female patients with PCDH19 gene-related epilepsy, rare episodes of status epilepticus occurred in about 30% of patients in the early course of the disorder.
In PCDH19 gene-related epilepsy, the seizures are often refractory to treatment, especially in infancy and childhood. Additionally, seizures are usually characterized by persistence of cluster seizures, with variable frequency. In a study of 35 female patients with PCDH19 gene-related epilepsy, approximately 30% had become seizure free in the girl's childhood (mean age of 12 years), yet some continued into adulthood. In the same study, a few patients still had recurrent cluster seizures that evolved into status epilepticus in childhood or early adolescence.
Developmental problems Beyond early-onset and treatment-resistant cluster seizures, PCDH19 gene-related epilepsy is usually, but not always, associated with cognitive and sensory impairment of varying degrees, and psychiatric and behavioral problems. It is estimated that up to 60 to 75% of females have cognitive deficits, ranging from mild to severe intellectual disability, which do not appear to be related to frequency or severity of seizures. Development over the course of a female patients' childhood can follow one of three courses: delays from birth that persist into adulthood, normal development and then regression, or normal intellectual development. It is not yet clear why some people experience delayed intellectual growth and others regress with epilepsy.
From the University of Melbourne study, two-thirds of PCDH19 gene-related epilepsy patients have borderline intellectual functioning or intellectual disability, while one third have normal intelligence. A connection to depression, autism, obsessive and aggressive behaviors and other disorders has been observed in PCDH19 gene-related epilepsy. Approximately 40-60% of girls diagnosed with a PCDH19 mutation are on the autism spectrum.
Many of those with PCDH19 gene mutations also exhibit behavioral and psychological problems – including ADHD, aggression, obsessive-compulsive disorder, and anxiety. Other neurological abnormalities may present, including sleep disturbances, ictal apnea, motor deficits, hypotonia, language delay, sensory integration problems and dysautonomia. Male carriers for this genetic mutation have been reported to exhibit neuropsychiatric features.
Causes A 2008 study found a relationship between the PCDH19 gene and early onset female seizures, with subsequent studies confirming the relationship.
PCDH19 gene-related epilepsy can arise as a single case in a family, due to a de novo error in cell replication, or it can be inherited. In a large series of cases in which inheritance was determined, half of the PCDH19 mutations occurred de novo, and half were inherited from fathers in good health, and who had no evidence of seizures or cognitive disorders.
Men and women can transmit the PCDH19 mutation, although females, but not males, usually, but not always, exhibit symptoms, which can be very mild. Females with a mutation have a 50% chance of having children who are carriers. Men have a 100% chance of transmitting the mutation to a daughter and 0% chance to a son.
Although males do not generally exhibit PCDH19 gene-related history such as cluster seizures, in a study involving four families with PCDH19 gene mutations, 5 of the fathers had obsessive and controlling tendencies. The linkage of chromosome Xq22.1 to PCDH19 gene-related epilepsy in females was confirmed in all of the families.
The inheritance pattern is very unusual, in that men that carry the PCDH19 gene mutation on their only X-chromosome are typically unaffected, except in rare instances of somatic mosaicism. Alternatively, approximately 90% of women who have the mutation on one of their two X-chromosomes exhibit symptoms. It has been suggested that the greater occurrence of PCDH19-epilepsy in females may relate to X-chromosome inactivation, through a hypothesized mechanism termed cellular interference.
A 2011 study found instances where patients had PCDH19 mutation, but their parents did not. They found that "gonadal mosaicism" of a PCDH19 mutation in a parent is an important molecular mechanism associated with the inheritance of a mutated PCDH19 gene.
Genetics The PCDH19 gene is located on the long (q) arm of the X chromosome at position 22.1. The mutations that most patients with the PCDH19-epilepsy occur within the first exon. The gene encodes for protocadherin 19, a transmembrane protein of calcium-dependent cell-cell adhesion molecules that is strongly expressed in neural tissue, such as the hippocampus, cerebral cortex, thalamus, and amygdala. Protocadherin 19 appears to be related to synaptic transmission and formation of synaptic connections during brain development.
A mutation in the PCDH19 gene can cause the protocadherin 19 protein to be malformed, reduced in function or not produced at all. This abnormal expression of protocadherin 19 causes deficits in GABAergic signaling, causing the occurrence of seizures beginning in the early years of life.
The expression of the PCDH19 mutation is highly variable, with some individuals appearing unaffected, and others showing severe disease. Even monozygotic twins with the mutation may have variations in seizure frequency and degree of cognitive impairment.
Currently, the PCDH19 gene is the second most clinically relevant gene in the epilepsy field; the second largest number of epilepsy related mutations characterized thus far occur in the PCDH19 gene. The SCN1A gene, associated with Dravet syndrome, is the most clinically relevant.
Diagnosis PCDH19 gene-related epilepsy is clinically based on patient and family seizure history, cognitive and behavioral neuropsychological evaluation, neurological examination, electroencephalogram (EEG) studies, and long term observation. Diagnosis is confirmed using molecular testing for PCDH19 mutations.
Diagnostic test The test is particularly indicated in children who have had cluster seizures in series. It is also recommended for patients who are diagnosed GEFS+ and when the seizures are associated with fever, infection, experienced regression, delayed cognitive growth or behavioral problems. The test is typically ordered by neurologists. The diagnostic test can be done by drawing blood or saliva of the patient and their immediate family. It is analyzed in laboratories that specialize in genetic testing. Genetic testing can aid in a firmer diagnosis and understanding of the disorder, may aid in identifying the optimal treatment plan and if positive, testing of the parents can determine if they are carriers as well as advising genetic counseling.
Classification Due to its recent discovery, PCDH19 gene-related epilepsy does not have a specific classification according to the International League Against Epilepsy.
PCDH19 gene-related epilepsy is thought to develop based upon a deficiency of the calcium-dependent cell-adhesion PCDH19 (protocadherin 19) gene. Its cause and pathophysiology (cause and mechanisms by which damage occurs) are different from other epilepsies, although the symptoms are very similar to other epileptic syndromes, such as Generalized epilepsy with febrile seizures plus (GEFS+), Dravet syndrome with SCN1A negative, FIRES (febrile infection–related epilepsy syndrome) Lennox-Gastaut syndrome or epilepsy of unknown origin.
Treatment
Medication Antiepileptic drugs (AEDs) are used in most cases to control seizures, however, PCDH19 gene-related epilepsy is generally associated with early-onset development of drug resistant seizures. Existing data supports the use of "rational polypharmacy," which consists of a step-wise addition of AEDs until a patient responds favorably or experiences intolerable adverse events. In general, as in other types of uncontrolled epilepsy, the use of drugs with different mechanisms of action appears to be more effective than combining drugs with similar mechanisms of action.
No currently marketed AEDs have been extensively studied in PCDH19 gene-related epilepsy and there is no established treatment strategy for girls diagnosed with PCDH19 gene-related epilepsy. Patients may respond well to treatment with levetiracetam and in cases of drug resistance, stiripentol, which is not approved in the U.S. but is available through the FDA Expanded Access IND process. Seizures might be easier to control with age, especially after the second decade of life. However, some publications have shown that medication withdrawal is highly associated with seizure recurrence.
Urgent care At the hospital, physicians follow standard protocol for managing seizures. Cluster seizures are generally controlled by benzodiazepines such as diazepam, midazolam, lorazepam or clonazepam. The use of oxygen is recommended in the United States, but in Europe it is only recommended in cases of prolonged epileptic status.
Epidemiology
The National Institute of Health Office and Rare Disease Research characterizes PCDH19 gene-related epilepsy as a rare disorder. Rare diseases, by definition, are diseases that affect fewer than 200,000 people in the United States. Since the mutation associated with PCDH19 gene-related epilepsy was only recently identified in 2008, the true incidence of the disease is generally unknown.