Chikahiko Numakura

Mitochondrial GTPase mitofusin 2 mutation in Charcot-Marie-Tooth neuropathy type 2A

Charcot–Marie–Tooth disease (CMT) has been classified into two types, CMT1 and CMT2, demyelinating and axonal forms, respectively. CMT2 has been further subdivided into eight groups by linkage studies. CMT2A is linked to chromosome 1p35–p36 and mutation in the kinesin family member 1B-ß (KIF1B) gene had been reported in one pedigree. However, no mutation in KIF1B was detected in other pedigrees with CMT2A and the mutations in the mitochondrial fusion protein mitofusin 2 (MFN2) gene were recently detected in those pedigrees. MFN2, a mitochondrial transmembrane GTPase, regulates the mitochondrial network architecture by fusion of mitochondria. We studied MFN2 in 81 Japanese patients with axonal or unclassified CMT and detected seven mutations in seven unrelated patients. Six of them were novel and one of them was a de novo mutation. Most mutations locate within or immediately upstream of the GTPase domain or within two coiled-coil domains, which are critical for the functioning or mitochondrial targeting of MFN2. Formation of a mitochondrial network would be required to maintain the functional peripheral nerve axon.

Small heat shock protein 27 mutation in a Japanese patient with distal hereditary motor neuropathy

AbstractHeat shock protein 27 (HSP27) belongs to a family of small heat shock proteins that play significant roles in the cellular stress response and are also involved in the control of protein-protein interactions as chaperons. Mutation in HSP27 has been identified as the cause of axonal Charcot-Marie-Tooth disease (CMT) and distal hereditary motor neuropathy (HMN). Heat shock protein 22 (HSP22) is a molecular counterpart of HSP27, and its mutation is another cause of distal HMN. We screened the mutation of HSP27 and HSP22 in 68 Japanese patients with axonal CMT or unclassified CMT and six Japanese patients with distal HMN. We detected a heterozygous P182S mutation of HSP27 in a patient with distal HMN, but we found no mutations in HSP22. Mutation in HSP27 may impair the formation of the stable neurofilament network that is indispensable for the maintenance of peripheral nerves.

Cytochrome P450 oxidoreductase deficiency: identification and characterization of biallelic mutations and genotype-phenotype correlations in 35 Japanese patients.

CONTEXT Cytochrome P450 oxidoreductase (POR) deficiency is a rare autosomal recessive disorder characterized by skeletal dysplasia, adrenal dysfunction, disorders of sex development (DSD), and maternal virilization during pregnancy. Although multiple studies have been performed for this condition, several matters remain to be clarified, including the presence of manifesting heterozygosity and the underlying factors for clinical variability. OBJECTIVE The objective of the study was to examine such unresolved matters by detailed molecular studies and genotype-phenotype correlations. PATIENTS Thirty-five Japanese patients with POR deficiency participated in the study. RESULTS Mutation analysis revealed homozygosity for R457H in cases 1-14 (group A), compound heterozygosity for R457H and one apparently null mutation in cases 15-28 (group B), and other combinations of mutations in cases 29-35 (group C). In particular, FISH and RT-PCR sequencing analyses revealed an intragenic microdeletion in one apparent R457H homozygote, transcription failure of apparently normal alleles in three R457H heterozygotes, and nonsense mediated mRNA decay in two frameshift mutation-positive cases examined. Genotype-phenotype correlations indicated that skeletal features were definitely more severe, and adrenal dysfunction, 46,XY DSD, and pubertal failure were somewhat more severe in group B than group A, whereas 46,XX DSD and maternal virilization during pregnancy were similar between two groups. Notable findings also included the contrast between infrequent occurrence of 46,XY DSD and invariable occurrence of 46,XX DSD and pubertal growth pattern in group A mimicking that of aromatase deficiency. CONCLUSIONS The results argue against the heterozygote manifestation and suggest that the residual POR activity reflected by the R457H dosage constitutes the underlying factor for clinical variability in some features but not other features, probably due to the simplicity and complexity of POR-dependent metabolic pathways relevant to each phenotype.

Neurofilament light chain polypeptide gene mutations in Charcot-Marie-Tooth disease : nonsense mutation probably causes a recessive phenotype

The neurofilament light chain polypeptide (NEFL) forms the major intermediate filament in neurons and axons. NEFL mutation is a cause of axonal or demyelinating forms of dominant Charcot–Marie–Tooth disease (CMT). We investigated NEFL in 223 Japanese CMT patients who were negative for PMP22, MPZ, GJB1, LITAF, EGR2, GDAP1, MTMR2 and PRX in the demyelinating form and negative for MFN2, MPZ, GJB1, HSP27, HSP22 and GARS in the axonal form. We detected four heterozygous missense mutations—Pro8Leu, Glu90Lys, Asn98Ser and Glu396Lys––in five unrelated patients and a homozygous nonsense mutation, Glu140Stop, in one other patient. All patients had mildly to moderately delayed nerve conduction velocities, possibly caused by a loss of large diameter fibers. This is the first report of a homozygous nonsense mutation of NEFL. Results of our study show that nonsense NEFL mutations probably cause a recessive phenotype, in contrast to missense mutations, which cause a dominant phenotype.

Molecular diagnosis and clinical onset of Charcot–Marie–Tooth disease in Japan

To study the genetic background of Japanese Charcot–Marie–Tooth disease (CMT) patients, we analyzed qualitative and quantitative changes in the disease-causing genes mainly by denaturing high performance liquid chromatography and multiplex ligation-dependent probe analysis in 227 patients with demyelinating CMT and 127 patients with axonal CMT. In demyelinating CMT, we identified 53 patients with PMP22 duplication, 10 patients with PMP22 mutations, 20 patients with MPZ mutations, eight patients with NEFL mutations, 19 patients with GJB1 mutations, one patient with EGR2 mutation, five patients with PRX mutations and no mutations in 111 patients. In axonal CMT, we found 14 patients with MFN2 mutations, one patient with GARS mutation, five patients with MPZ mutations, one patient with GDAP1 mutation, six patients with GJB1 mutations and no mutations in 100 patients. Most of the patients carrying PMP22, MPZ, NEFL, PRX and MFN2 mutations showed early onset, whereas half of the patients carrying PMP22 duplication and all patients with GJB1 or MPZ mutations showing axonal phenotype were adult onset. Our data showed that a low prevalence of PMP22 duplication and high frequency of an unknown cause are features of Japanese CMT. Low prevalence of PMP22 duplication is likely associated with the mild symptoms due to genetic and/or epigenetic modifying factors.

Periaxin mutation causes early-onset but slow-progressive Charcot-Marie-Tooth disease

AbstractPeriaxin (PRX) plays a significant role in the myelination of the peripheral nerve. To date, seven nonsense or frameshift PRX mutations have been reported in six pedigrees with Dejerine-Sottas neuropathy or severe Charcot-Marie-Tooth neuropathy (CMT). We detected a PRX mutation in three patients in the screening of 66 Japanese demyelinating CMT patients who were negative for the gene mutation causing dominant or X-linked demyelinating CMT. Three unrelated patients were homozygous for a novel R1070X mutation and presented early-onset but slowly progressive distal motor and sensory neuropathies. Mutations lacking the carboxyl-terminal acidic domain may show loss-of-function effects and cause severe demyelinating CMT.

Various types of LRP5 mutations in four patients with osteoporosis- pseudoglioma syndrome: Identification of a 7.2-kb microdeletion using oligonucleotide tiling microarray

Osteoporosis‐pseudoglioma syndrome (OPS; OMIM 259770) is an autosomal‐recessive genetic disorder characterized by severe osteoporosis and visual disturbance from childhood. Biallelic mutations in the low‐density lipoprotein receptor‐related protein 5 gene (LRP5) have been frequently detected, while a subset of patients had only one or no detectable mutation. We report on the clinical and molecular findings of four unrelated Japanese patients with the syndrome. The four patients had typical skeletal and ocular phenotypes of OPS, namely severe juvenile osteoporosis and early‐onset visual disturbance, with or without mental retardation. We undertook standard PCR‐based sequencing for LRP5 and found four missense mutations (p.L145F, p.T244M, p.P382L, and p.T552M), one nonsense mutation (p.R1534X), and one splice site mutation (c.1584+1G>A) among four OPS patients. Although three patients had two heterozygous mutations, one had only one heterozygous splice site mutation. In this patient, RT‐PCR from lymphocytic RNA demonstrated splice error resulting in 63‐bp insertion between exons 7 and 8. Furthermore, the patient was found to have only mutated RT‐PCR fragment, implying that a seemingly normal allele did not express LRP5 mRNA. We then conducted custom‐ designed oligonucleotide tiling microarray analyses targeted to a 600‐kb genome region harboring LRP5 and discovered a 7.2‐kb microdeletion encompassing exons 22 and 23 of LRP5. We found various types of LRP5 mutations, including an exon‐level deletion that is undetectable by standard PCR‐based mutation screening. Oligonucleotide tiling microarray seems to be a powerful tool in identifying cryptic structural mutations.

Hemizygous mutation of the peripheral myelin protein 22 gene associated with Charcot‐Marie‐Tooth disease type 1

We studied a female patient who presented with autosomal recessive or sporadic Charcot‐Marie‐Tooth disease type 1 (CMT1). We found that she had a 1.5‐megabase deletion in chromosome 17p11.2–p12 containing the peripheral myelin protein 22 gene (PMP22) and an Arg157Gly mutation of PMP22. Hemizygous mutation of PMP22 should be considered in patients with autosomal recessive CMT1 or with severe hereditary neuropathy with liability to pressure palsy. Ann Neurol 2000; 47:101–103

Molecular and Clinical Studies in 138 Japanese Patients with Silver-Russell Syndrome

Background Recent studies have revealed relative frequency and characteristic phenotype of two major causative factors for Silver-Russell syndrome (SRS), i.e. epimutation of the H19-differentially methylated region (DMR) and uniparental maternal disomy 7 (upd(7)mat), as well as multilocus methylation abnormalities and positive correlation between methylation index and body and placental sizes in H19-DMR epimutation. Furthermore, rare genomic alterations have been found in a few of patients with idiopathic SRS. Here, we performed molecular and clinical findings in 138 Japanese SRS patients, and examined these matters. Methodology/Principal Findings We identified H19-DMR epimutation in cases 1–43 (group 1), upd(7)mat in cases 44–52 (group 2), and neither H19-DMR epimutation nor upd(7)mat in cases 53–138 (group 3). Multilocus analysis revealed hyper- or hypomethylated DMRs in 2.4% of examined DMRs in group 1; in particular, an extremely hypomethylated ARHI-DMR was identified in case 13. Oligonucleotide array comparative genomic hybridization identified a ∼3.86 Mb deletion at chromosome 17q24 in case 73. Epigenotype-phenotype analysis revealed that group 1 had more reduced birth length and weight, more preserved birth occipitofrontal circumference (OFC), more frequent body asymmetry and brachydactyly, and less frequent speech delay than group 2. The degree of placental hypoplasia was similar between the two groups. In group 1, the methylation index for the H19-DMR was positively correlated with birth length and weight, present height and weight, and placental weight, but with neither birth nor present OFC. Conclusions/Significance The results are grossly consistent with the previously reported data, although the frequency of epimutations is lower in the Japanese SRS patients than in the Western European SRS patients. Furthermore, the results provide useful information regarding placental hypoplasia in SRS, clinical phenotypes of the hypomethylated ARHI-DMR, and underlying causative factors for idiopathic SRS.

Supernumerary impacted teeth in a patient with SOX2 anophthalmia syndrome.

SOX2 anophthalmia syndrome characteristically presents as anophthalmia or microphthalmia, with various extraocular symptoms, such as hypogonadotropic hypogonadism, brain anomaly, and esophageal abnormalities. In this report, we describe a patient with SOX2 anophthalmia syndrome complicated with a dental anomaly, multiple supernumerary impacted teeth, and persistence of deciduous teeth. Multiple supernumerary teeth are usually not solitary symptoms, but indicate systemic syndrome such as cleidocranial dysplasia. In odontogenesis, many transcriptional factors, such as BMPs, FGFs, and Wnts, play significant roles and SOX2 is known to interact with some of them. The role of SOX2 in dental development remains unknown, however, multiple supernumerary teeth can be considered as extraocular symptoms of SOX2 anophthalmia syndrome, rather than the coincidence of two rare diseases.