Demyelinating Charcot-Marie-Tooth neuropathy associated with FBLN5 mutations.

BACKGROUND AND PURPOSE: Charcot-Marie-Tooth disease type 1 (CMT1) is a group of autosomal dominantly inherited demyelinating sensorimotor neuropathies. Symptoms usually start in the first to second decade and include distal muscle weakness and wasting, sensory disturbances and foot deformities. The most frequent cause is a duplication of PMP22 whilst point mutations in PMP22 and other genes are rare causes. Recently, FBLN5 mutations have been reported in CMT1 families. METHODS: Individuals with FBLN5-associated CMT1 were compiled from clinical and research genetic testing laboratories. Clinical data were extracted from medical records or obtained during patients' visits at our centres or primary care sites. RESULTS: Nineteen CMT1 families containing 38 carriers of three different FBLN5 missense variants were identified and a mutational hotspot at c.1117C>T (p.Arg373Cys) was confirmed. Compared to patients with the common PMP22 duplication, individuals with FBLN5 variants had a later age of diagnosis (third to fifth decade) and less severely reduced motor median nerve conduction velocities (around 31 m/s). The most frequent clinical presentations were prominent sensory disturbances and painful sensations, often as initial symptom and pronounced in the upper limbs, contrasting with rather mild to moderate motor deficits. CONCLUSIONS: Our study confirms the relevance of FBLN5 mutations in CMT1. It is proposed to include FBLN5 in the genetic work-up of individuals suspected with CMT1, particularly when diagnosis is established beyond the first and second decade and comparably moderate motor deficits contrast with early and marked sensory involvement. FBLN5-associated CMT1 has a recognizable clinical phenotype and should be referred to as CMT1H according to the current classification scheme.

Novel SBF2 mutations and clinical spectrum of Charcot-Marie-Tooth neuropathy type 4B2.

Biallelic SBF2 mutations cause Charcot-Marie-Tooth disease type 4B2 (CMT4B2), a sensorimotor neuropathy with autosomal recessive inheritance and association with glaucoma. Since the discovery of the gene mutation, only few additional patients have been reported. We identified seven CMT4B2 families with nine different SBF2 mutations. Revisiting genetic and clinical data from our cohort and the literature, SBF2 variants were private mutations, including exon-deletion and de novo variants. The neuropathy typically started in the first decade after normal early motor development, was predominantly motor and had a rather moderate course. Electrophysiology and nerve biopsies indicated demyelination and excess myelin outfoldings constituted a characteristic feature. While neuropathy was >90% penetrant at age 10 years, glaucoma was absent in ~40% of cases but sometimes developed with age. Consequently, SBF2 mutation analysis should not be restricted to individuals with coincident neuropathy and glaucoma, and CMT4B2 patients without glaucoma should be followed for increased intraocular pressure. The presence of exon-deletion and de novo mutations demands comprehensive mutation scanning and family studies to ensure appropriate diagnostic approaches and genetic counseling.

Extension of the phenotype of biallelic loss-of-function mutations in SLC25A46 to the severe form of pontocerebellar hypoplasia type I.

Biallelic mutations in SLC25A46, encoding a modified solute transporter involved in mitochondrial dynamics, have been identified in a wide range of conditions such as hereditary motor and sensory neuropathy with optic atrophy type VIB (OMIM: *610826) and congenital lethal pontocerebellar hypoplasia (PCH). To date, 18 patients from 13 families have been reported, presenting with the key clinical features of optic atrophy, peripheral neuropathy, and cerebellar atrophy. The course of the disease was highly variable ranging from severe muscular hypotonia at birth and early death to first manifestations in late childhood and survival into the fifties. Here we report on 4 patients from 2 families diagnosed with PCH who died within the first month of life from respiratory insufficiency. Patients from 1 family had pathoanatomically proven spinal motor neuron degeneration (PCH1). Using exome sequencing, we identified biallelic disease-segregating loss-of-function mutations in SLC25A46 in both families. Our study adds to the definition of the SLC25A46-associated phenotypic spectrum that includes neonatal fatalities due to PCH as the severe extreme.

Molecular characterization of congenital myasthenic syndromes in Spain.

Congenital myasthenic syndromes (CMS) are a heterogeneous group of genetic disorders, all of which impair neuromuscular transmission. Epidemiological data and frequencies of gene mutations are scarce in the literature. Here we describe the molecular genetic and clinical findings of sixty-four genetically confirmed CMS patients from Spain. Thirty-six mutations in the CHRNE, RAPSN, COLQ, GFPT1, DOK7, CHRNG, GMPPB, CHAT, CHRNA1, and CHRNB1 genes were identified in our patients, with five of them not reported so far. These data provide an overview on the relative frequencies of the different CMS subtypes in a large Spanish population. CHRNE mutations are the most common cause of CMS in Spain, accounting for 27% of the total. The second most common are RAPSN mutations. We found a higher rate of GFPT1 mutations in comparison with other populations. Remarkably, several founder mutations made a large contribution to CMS in Spain: RAPSN c.264C > A (p.Asn88Lys), CHRNE c.130insG (Glu44Glyfs*3), CHRNE c.1353insG (p.Asn542Gluf*4), DOK7 c.1124_1127dup (p.Ala378Serfs*30), and particularly frequent in Spain in comparison with other populations, COLQ c.1289A > C (p.Tyr430Ser). Furthermore, we describe phenotypes and distinguishing clinical signs associated with the various CMS genes which might help to identify specific CMS subtypes to guide diagnosis and management.

Warburg micro syndrome type 1 associated with peripheral neuropathy and cardiomyopathy.

The Warburg micro syndrome (WARBM) is a genetically heterogeneous syndrome linked to at least 4 loci. At the clinical level, WARBM is characterized by microcephaly, microphthalmia, microcornea, congenital cataracts, corpus callosum hypoplasia, severe mental retardation, and hypogonadism. In some families additional clinical features have been reported. The presence of uncommon clinical features (peripheral neuropathy, cardiomyopathy) may result in misdirected molecular diagnostics. Using the next generation sequencing approach (NGS), we were able to diagnose WARBM1 syndrome by detection of a new mutation within the RAB3GAP1 gene. We have detected some DNA variants which may be responsible for cardiomyopathy. We did not find any obvious pathogenic mutation within a set of genes known to be responsible for hereditary motor and sensory neuropathy (HMSN). We conclude that: (i) in clinically delineated syndromes, a classical single-gene oriented approach may be not conclusive especially in the presence of rare clinical features, (ii) peripheral neuropathy and cardiomyopathy are rare additional symptoms coexisting with WARBM1, (iii) a pleiotropic effect of a single point mutation is sufficient to be causative for WARBM1 and (iv) more WARBM-affected patients should be reported to delineate a complete phenotype.

Diagnostic algorithms in Charcot-Marie-Tooth neuropathies: experiences from a German genetic laboratory on the basis of 1206 index patients.

We present clinical features and genetic results of 1206 index patients and 124 affected relatives who were referred for genetic testing of Charcot-Marie-Tooth (CMT) neuropathy at the laboratory in Aachen between 2001 and 2012. Genetic detection rates were 56% in demyelinating CMT (71% of autosomal dominant (AD) CMT1/CMTX), and 17% in axonal CMT (24% of AD CMT2/CMTX). Three genetic defects (PMP22 duplication/deletion, GJB1/Cx32 or MPZ/P0 mutation) were responsible for 89.3% of demyelinating CMT index patients in whom a genetic diagnosis was achieved, and the diagnostic yield of the three main genetic defects in axonal CMT (GJB1/Cx32, MFN2, MPZ/P0 mutations) was 84.2%. De novo mutations were detected in 1.3% of PMP22 duplication, 25% of MPZ/P0, and none in GJB1/Cx32. Motor nerve conduction velocity was uniformly <38 m/s in median or ulnar nerves in PMP22 duplication, >40 m/s in MFN2, and more variable in GJB1/Cx32, MPZ/P0 mutations. Patients with CMT2A showed a broad clinical severity regardless of the type or position of the MFN2 mutation. Out of 75 patients, 8 patients (11%) with PMP22 deletions were categorized as CMT1 or CMT2. Diagnostic algorithms are still useful for cost-efficient mutation detection and for the interpretation of large-scale genetic data made available by next generation sequencing strategies.

Molecular genetics of charcot-marie-tooth disease: from genes to genomes.

Charcot-Marie-Tooth disease (CMT) is a heterogeneous group of disorders of the peripheral nervous system, mainly characterized by distal muscle weakness and atrophy leading to motor handicap. With an estimated prevalence of 1 in 2,500, this condition is one of the most commonly inherited neurological disorders. Mutations in more than 30 genes affecting glial and/or neuronal functions have been associated with different forms of CMT leading to a substantial improvement in diagnostics of the disease and in the understanding of implicated pathophysiological mechanisms. However, recent data from systematic genetic screening performed in large cohorts of CMT patients indicated that molecular diagnosis could be established only in ∼50-70% of them, suggesting that additional genes are involved in this disease. In addition to providing an overview of genetic and functional data concerning various CMT forms, this review focuses on recent data generated through the use of highly parallel genetic technologies (SNP chips, sequence capture and next-generation DNA sequencing) in CMT families, and the current and future impact of these technologies on gene discovery and diagnostics of CMTs.

5q31 Microdeletions: Definition of a Critical Region and Analysis of LRRTM2, a Candidate Gene for Intellectual Disability.

Microdeletions including 5q31 have been reported in only few patients to date. Apart from intellectual disability/developmental delay (ID/DD) of varying degrees, which is common to all reported patients, the clinical spectrum is wide and includes short stature, failure to thrive, congenital heart defects, encephalopathies, and dysmorphic features. We report a patient with a 0.9-Mb de novo deletion in 5q31.2, the smallest microdeletion in 5q31 reported thus far. His clinical presentation includes mild DD, borderline short stature, postnatal microcephaly, and mild dysmorphic signs including microretrognathia. Together with data from 7 reported overlapping microdeletions, analysis of our patient enabled the tentative delineation of a phenotype map for 5q31 deletions. In contrast to the mild phenotype of small microdeletions affecting only 5q31.2, carriers of larger microdeletions which also include subbands 5q31.1 and/or 5q31.3 seem to be more severely affected with congenital malformations, growth anomalies, and severe encephalopathies. A 240-kb smallest region of overlap in 5q31.2 is delineated which contains only 2 genes, CTNNA1 and LRRTM2. We propose LRRTM2 as the most promising candidate gene for ID/DD due to its expression pattern, function as a key regulator of excitatory development, and interaction with Neurexin 1. However, sequence analysis of LRRTM2 in 330 patients with ID/DD revealed no relevant alterations, excluding point mutations in LRRTM2 as a frequent cause of ID/DD in patients without microdeletions.

Proteasomal inhibition alters the trafficking of the neurotrophin receptor TrkA.

Neurotrophin receptors of the Trk family promote neuronal survival. The signal transduction of Trk receptors is regulated by endosomal trafficking. Monoubiquitination of receptor tyrosine kinases is an established signal for sorting of internalized receptors to late endosomes. The NGF receptor TrkA is sorted to late endosomes and undergoes ubiquitination, indicating a so far undefined regulatory role of proteasomal activity in the trafficking of TrkA. Surprisingly, we found that proteasomal inhibition alters the trafficking of TrkA from the late endosomal sorting pathway to the recycling pathway. Many neurodegenerative diseases are associated with impaired proteasomal activity. Thus, our study suggests that missorting of neurotrophic receptors might contribute to neuronal death in those neurodegenerative diseases that are known to be associated with impaired proteasomal function.

Mitofusin 2 gene mutation (R94Q) causing severe early-onset axonal polyneuropathy (CMT2A).

Charcot-Marie-Tooth disease (CMT) has been classified into two types: demyelinating forms (CMT1) and axonal forms (CMT2). Mutations in the CMT2A locus have been linked to the KIF1B and the mitofusin 2 (MFN2) genes. Here, we report a German patient with CMT2 with an underlying spontaneous mutation (c.281G-->A) in the MFN2 gene. Clinically, the patient presented with early-onset CMT that was not associated with additional central nervous system pathology. The disease course was rapidly progressive in the first years and slowed afterwards. We also suggest that single patients with early-onset axonal polyneuropathies should be screened for MFN2 mutations.

PDGF-B gene single-nucleotide polymorphisms are not predictive for disease onset or progression of IgA nephropathy.

BACKGROUND: Few genetic factors have been identified that determine susceptibility to and progression of IgA-nephropathy (IgAN). Given that IgAN is usually characterized by mesangioproliferative glomerulonephritis and that PDGF-B is of central pathophysiological relevance in this process, we analyzed four single-nucleotide polymorphisms (SNPs) of the PDGF-B gene to evaluate a possible association of these SNPs with disease onset and progression, histological grading and responses to ACE inhibitor (ACEi) therapy. METHODS: The total study population consisted of 195 IgAN patients (127 from southern Italy and 68 from northern Germany) and 200 healthy controls (100 from each region). All four SNPs were in Hardy-Weinberg equilibrium and genotype distributions did not differ between patients and controls in either region. RESULTS: SNP distribution in Italian patients reaching end-stage renal disease (n=45) also was not significantly different from patients maintaining a serum creatinine below 1.2 mg/dl (n=60) during 5.6 +/- 5.5 years of follow-up. Furthermore, we failed to detect significant effects of any SNP on the slope of 1/serum creatinine, proteinuria level or the antiproteinuric response to ACEi. Additionally, particular PDGF-B genotypes did not correlate with histological grading using the Lee classification. CONCLUSION: We conclude that none of the four PDGF-B SNPs is related to the onset of IgAN in two different populations and that none of them has a major influence on the course of IgAN.

Mutations in the gene encoding the Wnt-signaling component R-spondin 4 (RSPO4) cause autosomal recessive anonychia.

Anonychia is an autosomal recessive disorder characterized by the congenital absence of finger- and toenails. In a large German nonconsanguineous family with four affected and five unaffected siblings with isolated total congenital anonychia, we performed genomewide mapping and showed linkage to 20p13. Analysis of the RSPO4 gene within this interval revealed a frameshift and a nonconservative missense mutation in exon 2 affecting the highly conserved first furin-like cysteine-rich domain. Both mutations were not present among controls and were shown to segregate with the disease phenotype. RSPO4 is a member of the recently described R-spondin family of secreted proteins that play a major role in activating the Wnt/ beta -catenin signaling pathway. Wnt signaling is evolutionarily conserved and plays a pivotal role in embryonic development, growth regulation of multiple tissues, and cancer development. Our findings add to the increasing body of evidence indicating that mesenchymal-epithelial interactions are crucial in nail development and put anonychia on the growing list of congenital malformation syndromes caused by Wnt-signaling-pathway defects. To the best of our knowledge, this is the first gene known to be responsible for an isolated, nonsyndromic nail disorder.

Submicroscopic unbalanced translocation resulting in del10p/dup13q detected by subtelomere FISH.

Chromosomal rearrangements involving the (sub)telomeres are an important cause of human genetic diseases: with the development of advanced molecular cytogenetic methods they have been identified as a major cause of mental retardation and/or congenital malformation syndromes. We identified a cryptic unbalanced de novo translocation 10p/13q by subtelomere FISH in a boy with mental and growth retardation (karyotype: 46,XY,der(10)t(10;13)(p15.1;q34)(D10S2488-,D13S296+)). Craniofacial dysmorphisms included frontal bossing, epicanthal folds, long philtrum, thin upper lip, short nose, mild retrognathy and a flat midface. In addition the patient had ASDII, a pyloric stenosis, bilateral inguinal hernias and cryptorchidism. His psychomotor development was significantly delayed. Microsatellite typing revealed the paternal origin of the two chromosomes involved in the rearrangement. By comparing our case with previously published patients with similar aberrations we conclude that the congenital malformations in our case are associated with the partial 10p deletion. The craniofacial features might be attributed to the 13q duplication. The identification of a 10p/13q translocation in our case highlights the importance of searching for cryptic subtelomeric imbalances in mentally retarded patients and helps to further delineate genotype-phenotype correlations in rare chromosomal disturbances.

Spine deformities in Charcot-Marie-Tooth 4C caused by SH3TC2 gene mutations.

BACKGROUND: Charcot-Marie-Tooth (CMT) disease is a heterogeneous group of inherited peripheral motor and sensory neuropathies with several modes of inheritance: autosomal dominant, X-linked, and autosomal recessive (AR) CMT. A locus responsible for the demyelinating form of ARCMT was assigned to the 5q23-q33 region (CMT4C) by homozygosity mapping. Recently, 11 mutations were identified in the SH3TC2 (KIAA1985) gene in 12 families with demyelinating ARCMT from Turkish, Iranian, Greek, Italian, or German origin. OBJECTIVE: To identify mutations in the SH3TC2 gene. METHODS: The authors searched for SH3TC2 gene mutations in 10 consanguineous CMT families putatively linked to the CMT4C locus on the basis of haplotype segregation and linkage analysis. RESULTS: Ten families had mutations, eight of which were new and one, R954X, recurrent. Six of the 10 mutations were in exon 11. Onset occurred between ages 2 and 10. Scoliosis or kyphoscoliosis and foot deformities were found in almost all patients and were often inaugural. The median motor nerve conduction velocity values (

Multi-exon deletions of the PKHD1 gene cause autosomal recessive polycystic kidney disease (ARPKD).

BACKGROUND: Autosomal recessive polycystic kidney disease (ARPKD) is caused by mutations in the PKHD1 (polycystic kidney and hepatic disease 1) gene on chromosome 6p12, a large gene spanning 470 kb of genomic DNA. So far, only micromutations in the 66 exons encoding the longest open reading frame (ORF) have been described, and account for about 80% of mutations. OBJECTIVE: To test the hypothesis that gross genomic rearrangements and mutations in alternatively spliced exons contribute to a subset of the remaining disease alleles. METHODS: Using DHPLC for alternatively spliced exons and quantitative real time polymerase chain reaction to detect genomic imbalances, 58 ARPKD patients were screened, of whom 55 were known to harbour one PKHD1 point mutation in the longest ORF. RESULTS: Three different heterozygous PKHD1 deletions and several single nucleotide changes in alternatively spliced exons were identified. The detected partial gene deletions are most likely pathogenic, while a potential biological function of the alterations identified in alternatively spliced exons must await the definition of transcripts containing alternative exons and their predicted reading frames. CONCLUSIONS: Gross PKHD1 deletions account for a detectable proportion of ARPKD cases. Screening for major genomic PKHD1 rearrangements will further improve mutation analysis in ARPKD.

New options for prenatal diagnosis in autosomal recessive polycystic kidney disease by mutation analysis of the PKHD1 gene.

Due to the poor prognosis of severe autosomal recessive polycystic kidney disease (ARPKD), there is a strong demand for prenatal diagnosis (PD). Reliable PD testing is possible by molecular genetic analysis only. Although haplotype-based analysis is feasible in most cases, it is associated with a risk of misdiagnosis in families without pathoanatomically proven diagnosis. Linkage analysis is impossible in families where DNA of the index patient is not available. Direct mutation analysis of the recently identified polycystic kidney and hepatic disease 1 gene opens new options in families to whom a reliable PD cannot be offered on the basis of linkage analysis. We for the first time report two cases with PD based on mutation detection, illustrating the new options for PD in ARPKD.