Genetic, electrophysiological, and pathological studies on patients with SCN9A-related pain disorders.

BACKGROUND AND AIMS: Voltage-gated sodium channel Nav1.7, encoded by the SCN9A gene, has been linked to diverse painful peripheral neuropathies, represented by the inherited erythromelalgia (EM) and paroxysmal extreme pain disorder (PEPD). The aim of this study was to determine the genetic etiology of patients experiencing neuropathic pain, and shed light on the underlying pathogenesis. METHODS: We enrolled eight patients presenting with early-onset painful peripheral neuropathies, consisting of six cases exhibiting EM/EM-like disorders and two cases clinically diagnosed with PEPD. We conducted a gene-panel sequencing targeting 18 genes associated with hereditary sensory and/or autonomic neuropathy. We introduced novel SCN9A mutation (F1624S) into a GFP-2A-Nav1.7rNS plasmid, and the constructs were then transiently transfected into HEK293 cells. We characterized both wild-type and F1624S Nav1.7 channels using an automated high-throughput patch-clamp system. RESULTS: From two patients displaying EM-like/EM phenotypes, we identified two SCN9A mutations, I136V and P1308L. Among two patients diagnosed with PEPD, we found two additional mutations in SCN9A, F1624S (novel) and A1632E. Patch-clamp analysis of Nav1.7-F1624S revealed depolarizing shifts in both steady-state fast inactivation (17.4 mV, p < .001) and slow inactivation (5.5 mV, p < .001), but no effect on channel activation was observed. INTERPRETATION: Clinical features observed in our patients broaden the phenotypic spectrum of SCN9A-related pain disorders, and the electrophysiological analysis enriches the understanding of genotype-phenotype association caused by Nav1.7 gain-of-function mutations.

Clinical and genetic investigation of 17 Japanese patients with hyperekplexia.

AIM: The aim of the study was to determine clinical and genetic characteristics of Japanese patients with hyperekplexia. METHOD: Clinical courses, responses to antiepileptic drugs, outcomes, and genetic testing were investigated in 17 Japanese patients (nine males, eight females, median age 1y, range birth-45y) with hyperekplexia. RESULTS: In all patients, muscle stiffness and startle responses appeared soon after birth. Only seven patients were diagnosed with hyperekplexia before 1 year of age. Seven patients had been misdiagnosed with other disorders such as epilepsy and adult-onset anxiety neurosis. Umbilical/inguinal hernias were seen in 10 patients. Life-threatening events were noted in four patients. Clonazepam was the most effective drug. Muscle stiffness completely disappeared in 12 patients before 5 years of age, whereas startle responses resolved in only three patients. Mutations in the GLRA1 and GLRB genes were identified in 16 patients and one patient respectively. In 14 patients, the mutation showed autosomal dominant inheritance; in the other three, inheritance was autosomal recessive. p.R271Q of GLRA1 was the most frequent mutation, found in 10 patients. Novel mutations, p.A272P and p.A384P of GLRA1, were detected. Clinical severity and outcome varied even in the same family. INTERPRETATION: Early correct diagnosis is essential for prevention of accidental injuries and to provide appropriate treatments for hyperekplexia. Clonazepam is effective, although the time taken for startle responses to resolve varied.

[Remarkable effect of a modified ketogenic diet in a boy with focal seizures followed by epileptic spasms in a cluster].

A modified ketogenic diet was demonstrated to be remarkably effective in a child with intractable symptomatic focal epilepsy with combined seizures of focal seizures and epileptic spasms (ES) in a cluster (ESC). ES started at 8 months of age and disappeared with ACTH therapy. At the age of 13 months, the child began to have intractable focal seizures that, later, were followed by ESC 10 times a day. Brain MRI showed only a non-specific diffuse cerebral atrophy. Interictal EEG showed high amplitude diffuse disorganized slow waves with prominent sharp waves predominant over the bilateral occipital region. We started a modified ketogenic diet (mKD) treatment without fasting or a water/calorie limitation. Since the 20th day of mKD, the patient has been seizure free (6 months) without adverse effects. EEG showed remarkable improvement and he has some improvement in the developmental milestones. A modified ketogenic diet is easier to start and continue compared to the classic ketogenic diet, and should be tried in intractable epilepsies that are not treatable surgically early in life from the developmental prognosis point of view.

[Effectiveness of topiramate in eleven patients with Dravet syndrome].

Dravet syndrome is a rare, but highly refractory epilepsy syndrome. As conventional drugs are not effective, introduction of new effective drugs in clinical use will benefit patients with this disease. We assessed the effectiveness of topiramate (TPM) as adjunctive therapy in 11 patients with Dravet syndrome. TPM was started at doses ranging from 10 to 50 mg/day (0.57 to 2.0 mg/kg/day), and the dosage was increased gradually up to the maximum dose (9 mg/kg/day) depending on efficacy and tolerability. The frequencies of convulsive seizures (generalized tonic-clonic seizures, unilateral seizures, partial onset generalized tonic-clonic seizures) during two months before starting TPM, two months after starting TPM, and the fifth and sixth months after starting TPM were determined. The mean dose (mean +/- SD) of TPM at the second month was 2.7 +/- 1.5 mg/kg/day (1.0-5.7 mg/kg/day, n= 11), and that at the sixth month was 4.5 +/- 2.2 mg/kg/day (1.0-7.3 mg/kg/day, n=10). Evaluation at the second month revealed that one of 11 patients (9%) became seizure-free, six patients (54%) showed greater than 50% seizure reduction, three patients (27%) showed less than 50% seizure reduction, and one patient (9%) had aggravation of convulsive seizures resulting in discontinuation of TPM at the first month. Evaluation at the sixth month revealed that one of 10 patients (10%) was seizure-free, seven patients (70%) had greater than 50% seizure reduction, two patients (20%) had less than 50% seizure reduction, and no patient (0%) had aggravation. Adverse effects were observed in five patients; dizziness in three patients, sleepiness in three patients, and oligohidrosis in one patient. In the present study, TPM was useful as an adjunctive therapy to reduce the frequency of convulsive seizures in patients with Dravet syndrome. A large-scale efficacy study of TPM for Dravet syndrome is warranted.

A 14-year-old girl with hyperekplexia having GLRB mutations.

Hyperekplexia manifests as generalized stiffness and an excessive startle reflex to stimuli. It starts in the neonatal period and is transmitted in many cases via autosomal dominant inheritance. The etiology is an abnormality of the glycinergic neurotransmission system that is involved in inhibitory neurotransmission. Aberrations of five genes related to this neurotransmission system have been identified. The patient was a 14-year-old girl with mild mental retardation. None of her family members had a neuromuscular disease. An excessive startle reflex and generalized stiffness were noted immediately after birth and she was diagnosed with epilepsy because epileptic discharges were observed. However, the disease was resistant to various antiepileptic drugs and the startle responses persisted. GLRB gene mutations (R50X/Q216fsx222) were identified, after which the patient was diagnosed with hyperekplexia. The startle reflex improved when clonazepam treatment was initiated. When patients have a persistent startle reflex, it is necessary to consider hyperekplexia, even if epileptic discharges are observed. Only four cases with GLRB mutations, including the present patient, have been reported. To make a definite diagnosis of hyperekplexia, it may be useful to screen for genes that are involved in the glycinergic neurotransmission system.

Immunomodulatory therapy versus surgery for Rasmussen syndrome in early childhood.

We examined seizure, cognitive, and motor outcomes in patients with Rasmussen syndrome or Rasmussen encephalitis (RS), after recent initiation of immunomodulatory therapies. Among 53 patients with a diagnosis of RS referred from all over Japan, 49 patients (male 22, female 27) with symptoms and findings characteristic of RS were evaluated. Regular intravenous immunoglobulin (IVIg) therapy was administered at a dose of 100mg/kg/day, etc. Regular steroid pulse therapy was conducted with methylprednisolone at a dose of 30mg/kg/day (children) or 1000mg/day (adults) for 3days. Tacrolimus was given at an initial dose of 0.1mg/kg/day (children). Mean onset age was 8.7±10.5years. Seizure-free rate was 71% after treatment by functional hemispherectomy (FH), and response rate for seizures was 81% by regular steroid pulse therapy, 42% by tacrolimus therapy, and 23% by regular IVIg therapy. Rate of patients with IQ higher than 80 (R80) was 50% by regular steroid pulse therapy, 43% by regular IVIg therapy, 29% by tacrolimus therapy, and 0% by FH. R80 after regular steroid pulse therapy was 100% in patients without MRI lesions, and 37% in those with advanced MRI lesions. Improvement of motor function (paresis) was observed only by immunomodulatory therapy. Motor function was aggravated in 100% of patients treated by FH, 62% by regular IVIg, and 10% by regular steroid pulse therapy. We suggest a new treatment strategy for RS using early immunomodulatory therapy: initiation of regular steroid pulse therapy after early diagnosis indicated by biomarkers, then switching to tacrolimus therapy after several months.