Epidemiological investigation of spinal muscular atrophy in Japan.

BACKGROUND: International reporting of epidemiological surveys of spinal muscular atrophy (SMA) in Japan has been limited to Shikoku, despite the epidemiology of the disease in countries worldwide becoming clearer. Treatments of 5q-SMA have been developed, and epidemiological studies are needed. PURPOSE: This study aimed to conduct a nationwide epidemiological survey of SMA in Japan to clarify the actual situation of SMA in Japan. METHOD: Patients with all clinical types of SMA, including neonates and adults, were selected from 1,005 medical facilities in Japan. RESULTS: As of December 2017, the actual number of reported patients with SMA was 658 and the genetic testing rate was 79.5%. The estimated number of patients was 1,478 (95% confidence interval (CI), 1,122-1,834), with a prevalence of 1.17 (95%CI, 0.89-1.45) per 100,000 people and an incidence of 0.51 (95%CI, 0.32-0.71) per 10,000 live births. Incidence rates of 5q-SMA by clinical type were 0.27 (95%CI, 0.17-0.38) and 0.08 (95%CI, 0.04-0.11) per 10,000 live births for type 1 and 2, respectively, in cases with a definitive diagnosis by genetic testing. We found that 363 cases (82.7%) occurred less than 2 years and 88 (20.0%) occurred age of 2 months old or under. CONCLUSION: This study clarifies the prevalence and incidence of SMA in Japan. As infantile onset accounts for most cases of SMA, newborn screening and subsequent treatment are important to save lives.

Progressive Atrial Conduction Defects Associated With Bone Malformation Caused by a Connexin-45 Mutation.

BACKGROUND: Inherited cardiac conduction disease is a rare bradyarrhythmia associated with mutations in various genes that affect action potential propagation. It is often characterized by isolated conduction disturbance of the His-Purkinje system, but it is rarely described as a syndromic form. OBJECTIVES: The authors sought to identify the genetic defect in families with a novel bradyarrhythmia syndrome associated with bone malformation. METHODS: The authors genetically screened 15 European cases with genotype-negative de novo atrioventricular (AV) block and their parents by trio whole-exome sequencing, plus 31 Japanese cases with genotype-negative familial AV block or sick sinus syndrome by targeted exon sequencing of 457 susceptibility genes. Functional consequences of the mutation were evaluated using an in vitro cell expression system and in vivo knockout mice. RESULTS: The authors identified a connexin-45 (Cx45) mutation (p.R75H) in 2 unrelated families (a de novo French case and a 3-generation Japanese family) who presented with progressive AV block, which resulted in atrial standstill without ventricular conduction abnormalities. Affected individuals shared a common extracardiac phenotype: a brachyfacial pattern, finger deformity, and dental dysplasia. Mutant Cx45 expressed in Neuro-2a cells showed normal hemichannel assembly and plaque formation. However, Lucifer yellow dye transfer and gap junction conductance between cell pairs were severely impaired, which suggested that mutant Cx45 impedes gap junction communication in a dominant-negative manner. Tamoxifen-induced, cardiac-specific Cx45 knockout mice showed sinus node dysfunction and atrial arrhythmia, recapitulating the intra-atrial disturbance. CONCLUSIONS: Altogether, the authors showed that Cx45 mutant p.R75H is responsible for a novel disease entity of progressive atrial conduction system defects associated with craniofacial and dentodigital malformation.

Relationships between long-term observations of motor milestones and genotype analysis results in childhood-onset Japanese spinal muscular atrophy patients.

AIM: To clarify the long-term natural history of SMA in Japanese patients by investigating the peak motor milestones of cases 7months through 57years of age, in efforts to contribute to evaluating outcomes of new therapeutic interventions. METHODS: We sub-classified 112 SMA type I-III cases into type Ia, type Ib, type IIa, type IIb, type IIIa and type IIIb, according to peak motor milestone achieved, and analyzed the SMN1, SMN2 and NAIP genes in relation to clinical subtypes. RESULTS: In type I cases, there was a significant difference (p<0.0001), depending on whether or not head control was obtained, in the time of ventilation support being required. In type II cases as well, the time at which the ability to maintain the sitting position independently was lost also differed significantly (p<0.01) between those acquiring the ability to sit unaided within eight months after birth and those acquiring this ability after eight months of age. In type III cases, being able versus unable to climb stairs was associated with a significant difference (p=0.02) in the median time until loss of walking independently. Positive correlations were also seen between copy numbers and the clinical severity of SMA. CONCLUSION: Our long-term results show peak motor milestone evaluations distinguishing between subtypes to be useful not only as outcome measures for assessing treatment efficacy in clinical trials but also for predicting the clinical courses of Japanese SMA patients.

Genetic Counseling for Couples Seeking Noninvasive Prenatal Testing in Japan: Experiences of Pregnant Women and their Partners.

The recent advent of noninvasive prenatal testing (NIPT) has had a significant impact in the field of prenatal testing. Although reports on pregnant women who used NIPT have accumulated, little is known about the experiences of their male partners. In this study, we assessed the experiences of couples who were expecting a child and undergoing NIPT, with a focus on both the pregnant women and their partners. Questionnaires were administered to 282 participants focusing on their specific experiences at three time points: after pre-test counseling (first visit), when undergoing NIPT (second visit), and when results were received (third visit). Responses were analyzed to assess the differences between pregnant women and their partners. We found that more partners selected "family" as their first information source about NIPT and "my partner" as the first person to request NIPT than did pregnant women (35.6 vs. 5.9 %; p < 0.001 and 19.3 vs.1.5 %; p < 0.001). However, pregnant women more often consulted others including family and friends until undergoing NIPT than their partners (89.1 vs. 54.6 %; p < 0.001). Our findings suggest that it is important to encourage male partners to be actively involved in the NIPT decision-making process. Differences between pregnant women and their partners should be seriously considered when providing genetic counseling.

Target resequencing of neuromuscular disease-related genes using next-generation sequencing for patients with undiagnosed early-onset neuromuscular disorders.

Neuromuscular disorders are clinically and genetically heterogeneous diseases with broadly overlapping clinical features. Progress in molecular genetics has led to the identification of numerous causative genes for neuromuscular disorders, but Sanger sequencing-based diagnosis remains labor-intensive and expensive because the genes are large, the genotypes and phenotypes of neuromuscular disorders overlap and multiple genes related to a single phenotype exist. Recently, the advent of next-generation sequencing (NGS) has enabled efficient, concurrent examination of several related genes. Thus, we used NGS for target resequencing of neuromuscular disease-related genes from 42 patients in whom undiagnosed early-onset neuromuscular disorders. Causative genes were identified in 19/42 (45.2%) patients (six, congenital muscular dystrophy; two, Becker muscular dystrophy (BMD); three, limb-girdle muscular dystrophy; one, concurrent BMD and Fukuyama congenital muscular dystrophy; three, nemaline myopathy; one, centronuclear myopathy; one, congenital fiber-type disproportion; one, myosin storage myopathy; and one, congenital myasthenic syndrome). We detected variants of uncertain significance in two patients. In 6/19 patients who received a definitive diagnosis, the diagnosis did not require muscle biopsy. Thus, for patients with suspected neuromuscular disorders not identified using conventional genetic testing alone, NGS-based target resequencing has the potential to serve as a powerful tool that allows definitive diagnosis.

Corticosteroid therapy for duchenne muscular dystrophy: improvement of psychomotor function.

BACKGROUND: Of the numerous clinical trials for Duchenne muscular dystrophy, only the corticosteroid prednisolone has shown potential for temporal improvement in motor ability. In this study, the effects of prednisolone on intellectual ability are examined in 29 cases of Duchenne muscular dystrophy because little information has been reported. And also, motor functions and cardiac functions were evaluated. METHODS: The treated group was administered prednisolone (0.75 mg/kg) orally on alternate days and the compared with the untreated control group. Gene mutations were investigated. The patients were examined for intelligence quotient adequate for age, brain natriuretic peptide, creatine kinase, and manual muscle testing before treatment and after the period 6 months to 2 years. RESULTS: Intelligence quotient scores of the treated increased to 6.5 ± 11.9 (mean ± standard deviation) were compared with the controls 2.1 ± 4.9 (P = 0.009). Intelligence quotient scores of the patients with nonsense point mutations improved significantly (21.0 ± 7.9) more than those with deletion or duplication (1.9 ± 9.0; P = 0.015). Motor function, such as time to stand up, of those treated improved significantly and brain natriuretic peptide level was reduced to a normal level after treatment in 15 patients (73%). CONCLUSIONS: Our results demonstrate the effectiveness of prednisolone in improving intellectual impairment as well as in preserving motor function and brain natriuretic peptide levels. We presume that prednisolone has a read-through effect on the stop codons in the central nervous systems of Duchenne muscular dystrophy because intelligence quotient of point mutation case was improved significantly.

MLL2 and KDM6A mutations in patients with Kabuki syndrome.

Kabuki syndrome is a congenital anomaly syndrome characterized by developmental delay, intellectual disability, specific facial features including long palpebral fissures and ectropion of the lateral third of the lower eyelids, prominent digit pads, and skeletal and visceral abnormalities. Mutations in MLL2 and KDM6A cause Kabuki syndrome. We screened 81 individuals with Kabuki syndrome for mutations in these genes by conventional methods (n = 58) and/or targeted resequencing (n = 45) or whole exome sequencing (n = 5). We identified a mutation in MLL2 or KDM6A in 50 (61.7%) and 5 (6.2%) cases, respectively. Thirty-five MLL2 mutations and two KDM6A mutations were novel. Non-protein truncating-type MLL2 mutations were mainly located around functional domains, while truncating-type mutations were scattered through the entire coding region. The facial features of patients in the MLL2 truncating-type mutation group were typical based on those of the 10 originally reported patients with Kabuki syndrome; those of the other groups were less typical. High arched eyebrows, short fifth finger, and hypotonia in infancy were more frequent in the MLL2 mutation group than in the KDM6A mutation group. Short stature and postnatal growth retardation were observed in all individuals with KDM6A mutations, but in only half of the group with MLL2 mutations.

Charcot-Marie-Tooth disease type 4C in Japan: report of a case.

INTRODUCTION: The distribution of documented cases of Charcot-Marie-Tooth disease type 4C (CMT4C) is mainly limited to the Mediterranean region. We report the first documented case of CMT4C in East Asia. Furthermore, we estimate the proportion of CMT4C in Japan and compare the same with that in European countries. CASE REPORT: A 72-year-old Japanese woman presented with early-onset motor and sensory neuropathy associated with scoliosis, deformities of the hands and feet, and carpal tunnel syndrome. A genetic screen detected a homozygous p.R529Q mutation in SH3TC2, the causative gene of CMT4C. The SH3TC2 mutation identified here is unique among 426 unrelated Japanese CMT patients, excluding those with CMT1A. CONCLUSIONS: Although CMT4C also occurs in Japan, it is less common than in European countries.

[Gene mutation and genetic counseling].

With the advance of technology of genetic research, a lot of genetic testing has been available as a clinical service. The genetic testing has sometimes been applied to not only diagnosis of a patient, but also pre-symptomatic diagnosis, prenatal diagnosis, carrier diagnosis, and susceptibility diagnosis. Genetic knowledge and psychological support are necessary for the subject for adequate voluntary decision making. Thus genetic counseling by a clinical geneticist or a genetic counselor is very important and must be offered on every genetic testing according to the Guidelines for genetic testing proposed by Genetic-Medicine-Related Societies.