PCDH19-Related Epilepsies

Protocadherin-19 (PCDH19) is considered one of the most relevant genes related to epilepsy. To date, more than 150 mutations have been identified as causative for PCDH19-female epilepsy (also known as early infantile epileptic encephalopathy-9, EIEE9), which is characterized by early onset epilepsy, intellectual disabilities, and behavioral disturbances. More recently, mosaic-males (i.e., exhibiting the variants in less than 25% of their cells) have been described as affected by infant-onset epilepsy associated with intellectual disability, as well as compulsive or aggressive behavior and autistic features. Although little is known about the physiological role of PCDH19 protein and the pathogenic mechanisms that lead to EIEE9, many reports and clinical observation seem to suggest a relevant role of this protein in the development of cellular hyperexcitability. However, a genotype–phenotype correlation is difficult to establish. The main feature of EIEE9 consists in early onset of seizures, which generally occur in clusters lasting 1 to 5 minutes and repeating up to 10 times a day for several days. Seizures tend to present during febrile episodes, similarly to the first phases of Dravet syndrome and PCDH19 variants have been found in ∼25% of females who present with features of Dravet syndrome and testing negative for SCN1A variants. There is no “standardized” treatment for PCDH19-related epilepsy and most of the patients receiving a combination of several drugs. In this review, we focus on the latest researches on these aspects, with regard to protein expression, its known functions, and the mechanisms by which the protein acts. The clinical phenotypes related to PCDH19 mutations are also discussed.

Calcium Channels Genes and Their Epilepsy Phenotypes

Calcium (Ca2+) channel gene mutations play an important role in the pathogenesis of neurological episodic disorders like epilepsy. CACNA1A and CACNA1H genes are involved in the synthesis of calcium channels. Mutations in the α1A subunit of the P/Q type voltage-gated calcium channel gene (CACNA1A) located in 19p13.13, which encodes for the transmembrane pore-forming subunit of CAV2.1 voltage-dependent calcium channel, have been correlated to a large clinical spectrum of epilepsy such as idiopathic genetic epilepsy, early infantile epilepsy, and febrile seizures. Moreover, CACNA1A mutations have been demonstrated to be involved in spinocerebellar ataxia type 6, familiar hemiplegic migraine, episodic ataxia type 2, early-onset encephalopathy, and hemiconvulsion–hemiplegia epilepsy syndrome. This wide phenotype heterogeneity associated with CACNA1A mutations is correlated to different clinical and electrophysiological manifestations. CACNA1H gene, located in 16p13.3, encodes the α1H subunit of T-type calcium channel, expressing the transmembrane pore-forming subunit Cav3.2. Despite data still remain controversial, it has been identified as an important gene whose mutations seem strictly related to the pathogenesis of childhood absence epilepsy and other generalized epilepsies. The studied variants are mainly gain-of-function, hence responsible for an increase in neuronal susceptibility to seizures. CACNA1H mutations have also been associated with autism spectrum disorder and other behavior disorders. More recently, also amyotrophic lateral sclerosis has been related to CACNA1H alterations. The aim of this review, other than describe the CACNA1A and CACNA1H gene functions, is to identify mutations reported in literature and to analyze their possible correlations with specific epileptic disorders, purposing to guide an appropriate medical treatment recommendation.

Aicardi–Goutières Syndrome Type 2: A Report on Two Cases with Different Phenotypes Caused by RNASEH2B Gene Mutations

Aicardi–Goutières syndrome (AGS) is a rare disorder characterized by acquired microcephaly, cerebral calcifications, leukodystrophy, cerebral atrophy, chronic lymphocytosis, and increased interferon-α in cerebrospinal fluid. We report on two children affected by AGS type 2, caused by mutations in RNASEH2B. The first child had the mutation c.529G > A (p.A177T) and presented with an atypical and mild phenotype, with delayed psychomotor development, calcifications of the brain white matter and basal ganglia, and interferon signature positivity. The disease course was stable. The second child presented the mutation c.554T > G (p.V185G) and showed a later onset (15 months) and a more progressive clinical course with functional inability in the upper limbs, steppage gait, and irritability. Despite immunoglobulin therapy, she developed to progressive tetraparesis and severe hypotonia. This case report highlights that RNASEH2B mutation cannot fully predict the phenotype of AGS type 2 when a mutation c.529G > A occurs. Moreover, an earlier symptomatology may be not related to a more severe prognosis or to a partial or absent response to treatment.

Optic Neuropathy, Secondary to Ethmoiditis, and Onodi Cell Inflammation during Childhood: A Case Report and Review of the Literature

Optic neuropathy consists of several etiological events. The primary etiologies of its acute form include optic neuritis, ischemic optic neuropathy, inflammatory (nondemyelinating) disorders, and trauma. Its subacute and chronic forms are most often linked to compressive, toxic, nutritional, or hereditary-genetic causes. Visual loss, dyschromatopsia, and visual field defects are the presenting symptoms. The Onodi cell (sphenoethmoidal air cell) is an anatomic variant located laterally and superior to the sphenoid sinus; it is closely related to the optic nerve. Onodi cell disorders are rare and may be unnoticed in differential diagnoses of patients with ocular and neurological manifestations. Here, we present the case of a 12-year-old boy with headache and acute loss of sight characterized by hemianopsia in the left eye and retrobulbar optic neuropathy caused by left sphenoethmoidal sinusitis with the presence of Onodi cell inflammation. The diagnosis was confirmed by multilayered paranasal computed tomography and cerebral magnetic resonance imaging. Therapeutic treatment resulted in gradual improvement: at the 2-week follow-up, the patient no longer had headaches and his visual acuity returned to normal. Inflammation of Onodi cells should be considered in children with headache and abnormal vision.

Encephalocraniocutaneous Lipomatosis (Haberland Syndrome or Fishman Syndrome)

Encephalocraniocutaneous lipomatosis is a sporadic, congenital neurocutaneous disorder characterized by the involvement of skin, central nervous system, and eye. A non-hereditary, autosomal mutation that may survive only in a mosaic state may be the cause of the clinical picture of the syndrome. Less than 80 patients have been so far reported and their clinical manifestations consisted of unilateral lipomatous hamartoma of the scalp or eyelid, epibulbar choristomas, and ipsilateral brain malformations. There is no clinical correlation between the severity of brain malformations and the clinical manifestations, and many patients with extremely extensive cerebral abnormalities are only minimal symptomatic. Seizures and mental retardation may also occur. The natural history is often favorable, without drug-resistant seizures and normal intelligence in most of the cases.

Characterization of a novel Brassica napus kinase, BNK1

A novel plant protein kinase, designated Brassica napus kinase 1 (BNK1), was isolated from a lambda-pistil cDNA library. The deduced BNK1 protein contains all eleven conserved subdomains of a kinase and encodes a functional serine/threonine protein kinase. Phylogenetic analysis of several plant protein kinase subfamilies showed that BNK1 is most closely related to the NAK subfamily of protein kinases. Genomic Southern blot analysis revealed that BNK1 is a single copy gene in the B. napus genome and does not appear to be a member of a multigene family. Expression studies revealed that the BNK1 transcript was ubiquitously expressed throughout the plant, with highest levels in stem and pistil tissues.

Further analysis of the interactions between the Brassica S receptor kinase and three interacting proteins (ARC1, THL1 and THL2) in the yeast two-hybrid system

The yeast two-hybrid system was used to further characterize the interactions between the Brassica S receptor kinase (SRK) and three putative substrates, ARC1 and the two thioredoxin h proteins, THL1 and THL2. Interactions were generally detectable with kinase domains of both Class I and Class II SRKs. Chimeric constructs were made between the SRK910 kinase domain and the non-interacting Arabidopsis RLK5 kinase domain. Only one chimeric construct, SRR2, interacted with THL1 and THL2, while none of the chimeras were able to interact with ARC1. SRR2 is largely made up of RLK5 kinase domain with the N-terminal end being derived from the SRK910 kinase domain and was the only chimeric construct that retained kinase activity. Deletion or substitution of a conserved cysteine at the N-terminal end of the SRK910 kinase domain resulted in loss of interaction with THL1 and THL2, while the addition of this cysteine to a related receptor kinase, SFR1, conferred the ability to interact with the thioredoxin h proteins. In addition, substitution of the cysteines in the THL1 active site abolished the interaction. Lastly, the two Arabidopsis thioredoxin h clones most closely related to THL1 and THL2 were found to interact with the SRK kinase domains. Thus, the nature of the interaction of the thioredoxin h clones with SRK involves the reducing activity of these proteins and is restricted to the class of thioredoxin h proteins which have the variant CPPC active site.

Binding of an arm repeat protein to the kinase domain of the S-locus receptor kinase

Screening of a yeast two-hybrid library for proteins that interact with the kinase domain of an S-locus receptor kinase (SRK) resulted in the isolation of a plant protein called ARC1 (Arm Repeat Containing). This interaction was mediated by the C-terminal region of ARC1 in which five arm repeat units were identified. Using the yeast two-hybrid system and in vitro binding assays, ARC1 was found to interact specifically with the kinase domains from SRK-910 and SRK-A14 but failed to interact with kinase domains from two different Arabidopsis receptor-like kinases. In addition, treatment with a protein phosphatase or the use of a kinase-inactive mutant reduced or abolished the binding of ARC1 to the SRK-910 kinase domain, indicating that the interaction was phosphorylation dependent. Lastly, RNA blot analysis revealed that the expression of ARC1 is restricted to the stigma, the site of the self-incompatibility response.

Two members of the thioredoxin-h family interact with the kinase domain of a Brassica S locus receptor kinase

To determine potential targets of the S locus receptor kinase (SRK) during the Brassica self-incompatibility response, a yeast two-hybrid library was screened with the SRK-910 protein kinase domain. Two thioredoxin-h-like clones, THL-1 and THL-2, were found to interact specifically with the SRK-910 protein kinase domain and not to interact with the protein kinase domains from the Arabidopsis receptor-like protein kinases (RLK) RLK4 and RLK5. The interaction between THL-1 and the SRK-910 protein kinase domain was confirmed using coimmunoprecipitation experiments with fusion proteins produced in Escherichia coli. THL-1 has thioredoxin activity based on an insulin reduction assay, and THL-1 is weakly phosphorylated by the SRK-910 protein kinase domain. THL-1 and THL-2 are both expressed in a variety of tissues but show some differences in steady state mRNA levels, with THL-2 being preferentially expressed in floral tissues. This indicates a more general biological function for these thioredoxins in addition to a potential role as effector molecules in the self-incompatibility signal cascade.