RANBP2 mutation in an Indian child with recurrent acute necrotizing encephalopathy

Roles of Nucleoporin RanBP2/Nup358 in Acute Necrotizing Encephalopathy Type 1 (ANE1) and Viral Infection

Ran Binding Protein 2 (RanBP2 or Nucleoporin358) is one of the main components of the cytoplasmic filaments of the nuclear pore complex. Mutations in the RANBP2 gene are associated with acute necrotizing encephalopathy type 1 (ANE1), a rare condition where patients experience a sharp rise in cytokine production in response to viral infection and undergo hyperinflammation, seizures, coma, and a high rate of mortality. Despite this, it remains unclear howRanBP2 and its ANE1-associated mutations contribute to pathology. Mounting evidence has shown that RanBP2 interacts with distinct viruses to regulate viral infection. In addition, RanBP2 may regulate innate immune response pathways. This review summarizes recent advances in our understanding of how mutations in RANBP2 contribute to ANE1 and discusses how RanBP2 interacts with distinct viruses and affects viral infection. Recent findings indicate that RanBP2 might be an important therapeutic target, not only in the suppression of ANE1-driven cytokine storms, but also to combat hyperinflammation in response to viral infections.

Radiological manifestation of familial acute necrotizing encephalopathy with RANBP2 mutation in a Far-East Asian family: Case report

RATIONALE

Acute necrotizing encephalopathy (ANE) is a specific type of encephalopathy usually followed by febrile infection. It has an aggressive clinical course; however, it usually does not recur after recovery in cases of spontaneous ANE. Nevertheless, there are several studies reporting recurrences in familial ANE with RAN-binding protein 2 (RANBP2) mutation. There are few cases of familial ANE with RANBP2 mutation in Asian populations.

PATIENTS CONCERNS

A 21-month-old Korean boy who was previously healthy, presented with seizure following parainfluenza - a virus and bocavirus infection, followed by 2 recurrent seizure episodes and encephalitis after febrile respiratory illnesses. Meanwhile, his 3-year-old sister had focal brain lesions on neuroimaging studies when evaluated for head trauma. The siblings also had an older brother who presented status epilepticus after febrile respiratory illness at the age of 10 months old.

DIAGNOSIS

Brain magnetic resonance imaging was performed to evaluate the seizure and neurologic symptoms. Imaging findings showed variable spectrum - from non-specific diffuse white matter injury pattern to typical "tricolor pattern" of the ANE on diffusion-weighted images. The other 2 siblings showed focal lesions in both external capsules and severe diffuse brain edema. Genetic tests identified a heterozygous missense mutation in the RANBP2 [c.1754C>T (p.Thr585Met)] in 2 siblings and their mother.

INTERVENTIONS

Patients were treated conservatively with anticonvulsive agents, intravascular immunoglobulin, and steroids.

OUTCOMES

Among the 3 siblings, 2 male siblings died from familial ANE, whereas the female sibling was asymptomatic.

LESSONS

These cases highlight the radiological aspects of familial ANE with incomplete penetrance of the RANBP2 gene in 3 family members, showing variable involvements of the brain and natural history on magnetic resonance images. Radiologists should be aware of the typical and atypical imaging findings of familial ANE for prompt management of affected patients.

Genetic Acute Necrotizing Encephalopathy Associated with RANBP2: Clinical and Therapeutic Implications in Pediatrics

Genetic (also known as familial) acute necrotizing encephalopathy (ANE1) is a rare disease presenting with encephalopathy often following preceding viral febrile illness in patients with a genetic predisposition resulting from a missense mutation in the gene encoding RAN Binding Protein 2 (RANBP2). The acute episode is characterized by deterioration in consciousness, often with focal neurologic deficits and seizures. Additionally, symmetric multifocal brain lesions are seen in the bilateral thalami as well as other characteristic regions, involving both gray and white matter. Prognosis is variable, with a high mortality rate and most surviving patients having persistent neurologic deficits. Early treatment with high dose steroids is associated with a more favorable outcome, however the diagnosis is often overlooked resulting in delayed treatment. The RANBP2 mutation associated with ANE1 causes an incompletely penetrant predisposition to encephalopathy in the setting of febrile illness through a mechanism that remains elusive. There are several non-mutually exclusive hypotheses suggesting possible etiologies for this phenotype based on the many functions of RANBP2 within the cell. These include dysfunctions in nucleocytoplasmic trafficking and intracellular metabolic regulation, as well as cytokine storm, and abnormal distribution of mitochondria. This narrative review explores these key concepts of the RANBP2 mutation and its clinical and therapeutic implications in pediatric populations.

Acute Necrotizing Encephalopathy of Childhood with H1N1 Infection

Acute necrotizing encephalopathy of childhood (ANEC) is an uncommon and fulminant complication of seasonal influenza infection associated with high mortality and poor neurological outcome. We report a 4.5-year-old female who had pneumonia, ANEC, and raised intracranial pressure (ICP) with polymerase chain reaction proven H1N1 infection. Management included mechanical ventilation, invasive monitoring and control of ICP, oseltamivir, methylprednisolone, and supportive care in pediatric intensive care unit. She survived with poor neurological status at discharge.

Acute Necrotizing Encephalopathy in Children: a Long Way to Go

BACKGROUND

Acute necrotizing encephalopathy (ANE) is a rare, but potentially life threatening neurological condition in children. This study aimed to investigate its clinical spectrum, diagnostic and therapeutic dilemma, and prognosis.

METHODS

Twelve children with ANE were included in the study. The diagnosis was made by clinical and radiological characteristics from January 1999 to December 2017 and their clinical data were retrospectively analyzed.

RESULTS

A total of 12 children aged 6 to 93 months at onset (5 male: 7 female) were evaluated. The etiology was found in 4 of them (influenza A, H1N1; coxsackie A 16; herpes simplex virus; and RANBP2 gene/mycoplasma). The most common initial presentations were seizures (67%) and altered mental status (58%). The majority of the subjects showed elevation of aspartate aminotransferase/alanine aminotransferase with normal ammonia and increased cerebrospinal fluid protein without pleocytosis. Magnetic resonance imaging revealed increased T2 signal density in bilateral thalami in all patients, but the majority of the subjects (67%) also had lesions in other areas including tegmentum and white matter. Despite the aggressive immunomodulatory treatments, the long-term outcome was variable. One child and two sisters with genetic predisposition passed away.

CONCLUSION

ANE is a distinctive type of acute encephalopathy with diverse clinical spectrum. Even though the diagnostic criteria are available, they might not be watertight. In addition, treatment options are still limited. Further studies for better outcome are needed.

Moonlighting nuclear pore proteins: tissue-specific nucleoporin function in health and disease

The nuclear pore complex is the main transportation hub for exchange between the cytoplasm and the nucleus. It is built from nucleoporins that form distinct subcomplexes to establish this huge protein complex in the nuclear envelope. Malfunctioning of nucleoporins is well known in human malignancies, such as gene fusions of NUP214 and NUP98 in hematological neoplasms and overexpression of NUP88 in a variety of human cancers. In the past decade, the incremental utilization of next-generation sequencing has unraveled mutations in nucleoporin genes in the context of an increasing number of hereditary diseases, often in a tissue-specific manner. It emerges that, on one hand, the central nervous system and the heart are particularly sensitive to mutations in nucleoporin genes. On the other hand, nucleoporins forming the scaffold structure of the nuclear pore complex are eminently mutation-prone. These novel and exciting associations between nucleoporins and human diseases emphasize the need to shed light on these unanticipated tissue-specific roles of nucleoporins that may go well beyond their role in nucleocytoplasmic transport. In this review, the current insights into altered nucleoporin function associated with human hereditary disorders will be discussed.

Familial acute necrotizing encephalopathy with RANBP2 mutation: The first report in Northeast Asia

BACKGROUND

Acute necrotizing encephalopathy (ANE) is a rare but rapidly progressing encephalopathy following a febrile illness, commonly a viral infection. It is characterized by the features of acute encephalopathy such as seizure, alteration of consciousness, and symmetric involvement of the bilateral thalamus on neuroimaging tests. Although most ANE cases have occurred sporadically, familial or recurrent ANE has been reported in Caucasian patients, with genetic susceptibility to ANE noted in some patients due to a RANBP2 mutation. We report the cases of two Korean siblings with typical ANE and RANBP2 mutation.

CASE REPORT

A 2year-old Korean girl presented with prolonged seizures and encephalopathy after two days of febrile illness. Brain computed tomography (CT) showed diffuse brain swelling and low attenuation in the bilateral thalamus. Two months later, her younger sister presented with lethargy and flurries of seizures after a Mycoplasma pneumoniae infection. Brain magnetic resonance imaging scan (MRI) showed a characteristic involvement of the bilateral thalamus, suggesting ANE. Although they received intravenous steroids and immunoglobulin, the older child died; her sister remained in a coma. Both were diagnosed with familial ANE after identifying a common missense mutation in RANBP2 (c.1754C>T: p.Thr585Met) in the younger sister and their father.

CONCLUSIONS

This report is the first case of familial ANE in Northeast Asia identifying a RANBP2 mutation with poor outcome. Due to rapidly deterioration and recurrent nature of familial ANE, genetic test of RANBP2 mutation should be considered for early diagnosis. Further studies are needed to elucidate the nature of ANE.