Jana Neupauerová

Spectrum and frequencies of mutations in the MFN2 gene and its phenotypical expression in Czech hereditary motor and sensory neuropathy type II patients

The axonal type of Charcot‑Marie‑Tooth (CMT) disorders is genetically heterogeneous, therefore the causal mutation is unlikely to be observed, even in clinically well characterized patients. Mitofusin‑2 (MFN2) gene mutations are the most frequent cause of axonal CMT disorders in a number of populations. There are two phenotypes; early onset, which is severe and late onset, which is a milder phenotype. A cohort of 139 unrelated Czech patients with axonal neuropathy was selected for sequencing and multiplex ligation-dependent probe amplification analysis (MLPA) testing of the MFN2 gene. A total of 11 MFN2 mutations were detected, with eight pathogenic mutations and three potentially rare benign polymorphisms. MLPA testing in 64 unrelated patients did not detect any exon duplication or deletion. The frequency of the pathogenic mutations detected in Czech hereditary motor and sensory neuropathy type II (HMSN II) patients was 7.2%. Early onset was more frequent among pathogenic mutation cases. Therefore we propose to examine the MFN2 gene mainly in patients with early and severe axonal CMT.

Mutations in eight small DFNB genes are not a frequent cause of non-syndromic hereditary hearing loss in Czech patients

OBJECTIVES To evaluate the contribution of eight small NSHL-AR (non-syndromic deafness, autosomal recessive) genes to hereditary hearing loss in Czech patients. PATIENTS AND METHODS Unrelated Czech patients, adults and children, diagnosed with pre-lingual hereditary hearing loss with at least one similarly affected deaf sibling and with previously excluded mutations in the GJB2 gene were investigated by Sanger sequencing of the selected eight small NSHL-AR associated genes (CABP2 - 51 patients, CIB2 - 45 patients, PJVK/DFNB59 - 53 patients, GJB3 - 46 patients, ILDR1 - 48 patients, LHFPL5 - 66 patients, LRTOMT - 60 patients, TMIE - 64 patients). RESULTS Mutations were detected in the LHFPL5 (DFNB67) gene. The patient is heterozygote for two already described pathogenic variants (p.Tyr127Cys, p.Thr165Met). In five samples, five rare heterozygous variants (two novel) predicted as pathogenic were detected in genes CABP2, ILDR1, LHFPL5 and LRTOMT. CONCLUSION Mutations in eight small NSHL-AR genes are not a frequent cause of hereditary hearing loss in the Czech Republic. This diagnostic approach permitted the clarification of HL in only one patient - two heterozygous mutations were detected in LHFPL5 gene for the first time in Central Europe. As the use of panel base MPS certainly improves the diagnostic yield, future studies should rather profit from that diagnostic strategy.

Czech family confirms the link between FBLN5 and Charcot–Marie–Tooth type 1 neuropathy

Sir, The article by Auer-Grumbach et al. (2011) reporting that fibulin 5 ( FBLN5 ) mutations are also linked to inherited neuropathies helped us to clarify the cause of autosomal dominant, demyelinating hereditary motor and sensory neuropathy (HMSN I) in our long-time known, but unsolved, Czech family. Before this study was published, mutations in FBLN5 were associated only with the connective tissue disorder cutis laxa (Loeys et al. , 2002; Markova et al. , 2003; Lotery et al. , 2006; Nascimento et al. , 2010) and age-related macular degeneration leading to vision loss in those aged >50 years (Stone et al. , 2004; Lotery et al. , 2006). Auer-Grumbach et al. (2011) were the first to describe a large family with demyelinating Charcot–Marie–Tooth (CMT1) and linkage with the interval on chromosome 14. Subsequent resequencing of this region revealed only one novel variant c.1117 C > T (p.R373C) segregating with the disease in the family. Additional screening of 112 patients with Charcot–Marie–Tooth disease showed two other sequence variations in two patients with pure motor neuropathy and hyperelastic skin. The linkage with log of odds score >3.31 indicates the FBLN5 mutation as highly probably causal for HMSN I, but no functional study to confirm this was performed, and no other study on FBLN5 mutations in a family with HMSN has been published to date. This Austrian HMSN I family is the only one reported worldwide. We report a second family with non-syndromic inherited demyelinating motor and sensory neuropathy (HMSN I) with FBLN5 mutation and confirm FBLN5 mutations as the new cause of HMSN I. We used exome sequencing for clarification of the cause of HMSN I in a Czech family recruited in 2001 (Fig. 1A). The most frequent causes of CMT1 (CMT1 duplication/HNPP …

COX6A1 mutation causes axonal hereditary motor and sensory neuropathy – the confirmation of the primary report

To the Editor In the September 2014 issue of the American Journal of Human Genetics, Tamiya et al. stated that a homozygous deletion c.247-10_247-6del CACTC in COX6A1 is a cause of axonal and intermediate autosomal recessive Charcot–Marie–Tooth disease in two families of Japanese origin (1). We report a patient with the same homozygous deletion. Our work confirms the link between COX6A1 mutations and hereditary neuropathy. We report a first patient with COX6A1 mutations outside Japan. This letter describes the phenotype of the patient in detail to support the primary report in the presentation of the disease, but also provides additional clinical features that were observed. Moreover, our data confirms a mutational hotspot which has been proposed by Tamyia et al. Last but not least, in our opinion, the correct nomenclature for the deletion should be: c.247-7_247-3del (not

Massively Parallel Sequencing Detected a Mutation in the MFN2 Gene Missed by Sanger Sequencing Due to a Primer Mismatch on an SNP Site

We describe a patient with early onset severe axonal Charcot‐Marie‐Tooth disease (CMT2) with dominant inheritance, in whom Sanger sequencing failed to detect a mutation in the mitofusin 2 (MFN2) gene because of a single nucleotide polymorphism (rs2236057) under the PCR primer sequence. The severe early onset phenotype and the family history with severely affected mother (died after delivery) was very suggestive of CMT2A and this suspicion was finally confirmed by a MFN2 mutation. The mutation p.His361Tyr was later detected in the patient by massively parallel sequencing with a gene panel for hereditary neuropathies. According to this information, new primers for amplification and sequencing were designed which bind away from the polymorphic sites of the patients DNA. Sanger sequencing with these new primers then confirmed the heterozygous mutation in the MFN2 gene in this patient. This case report shows that massively parallel sequencing may in some rare cases be more sensitive than Sanger sequencing and highlights the importance of accurate primer design which requires special attention.

Detection rate of causal variants in severe childhood epilepsy is highest in patients with seizure onset within the first four weeks of life

BackgroundEpilepsy is a heterogeneous disease with a broad phenotypic spectrum and diverse genotypes. A significant proportion of epilepsies has a genetic aetiology.In our study, a custom designed gene panel with 112 genes known to be associated with epilepsies was used. In total, one hundred and fifty-one patients were tested (86 males / 65 females).ResultsIn our cohort, the highest probability for the identification of the cause of the disease was for patients with a seizure onset within the first four weeks of life (61.9% clarification rate) – about two times more than other groups. The level of statistical significance was determined using a chi-square analysis.From 112 genes included in the panel, suspicious and rare variants were found in 53 genes (47.3%).Among the 151 probands included in the study we identified pathogenic variants in 39 patients (25.8%), likely pathogenic variants in three patients (2%), variants of uncertain significance in 40 patients (26.5%) and likely benign variants in 69 patients (45.7%).ConclusionOur report shows the utility of diagnostic genetic testing of severe childhood epilepsies in a large cohort of patients with a diagnostic rate of 25.8%. A gene panel can be considered as a method of choice for the detection of pathogenic variants within patients with unknown origin of early onset severe epilepsy.

Neonatal Onset of Epilepsy of Infancy with Migrating Focal Seizures Associated with a Novel GABRB3 Variant in Monozygotic Twins

Abstract Background Recently, a study providing insight into GABRB3 mutational spectrum was published (Møller et al 2017). The authors report considerable pleiotropy even for single mutations and were not able to identify any genotype‐phenotype correlations. Methods The proband (twin B) was referred for massively parallel sequencing of epilepsy‐related gene panel because of hypotonia and neonatal seizures. The revealed variant was confirmed with Sanger sequencing in the proband and the twin A, and both parents were tested for the presence of the variant. Results We report a case of epilepsy of infancy with migrating focal seizures (EIMFS) of neonatal onset in monozygotic twins with a de novo novel GABRB3 variant p.Thr281Ala. The variant has a uniform presentation on an identical genomic background. In addition, early seizure‐onset epilepsy associated with GABRB3 mutation has been until now described only for the p.Leu256Gln variant in the GABRB3 (Møller et al 2017, Myers et al 2016) located in the transmembrane domain just as the p.Thr281Ala variant described here. Conclusion De novo GABRB3 mutations may cause neonatal‐onset EIMFS with early‐onset hypotonia, respiratory distress, and severe developmental delay.

Genome-wide uniparental diploidy of all paternal chromosomes in an 11-year-old girl with deafness and without malignancy

Approximately 20 cases of genome-wide uniparental disomy or diploidy (GWUPD) as mosaicism have previously been reported. We present the case of an 11-year-old deaf girl with a paternal uniparental diploidy or isodisomy with a genome-wide loss of heterozygosity (LOH). The patient was originally tested for non-syndromic deafness, and the novel variant p.V234I in the ESRRB gene was found in a homozygous state. Our female proband is the seventh patient diagnosed with GWUPD at a later age and is probably the least affected of the seven, as she has not yet presented any malignancy. Most, if not all, reported patients with GWUPD whose clinical details have been published have developed malignancy, and some of those patient developed malignancy several times. Therefore, our patient has a high risk of malignancy and is carefully monitored by a specific outpatient pediatric oncology program. This observation seems to be novel and unique in a GWUPD patient. Our study is also unique as it not only provides very detailed documentation of the genomic situations of various tissues but also reports differences in the mosaic ratios between the blood and saliva, as well as a normal biparental allelic situation in the skin and biliary duct. Additionally, we were able to demonstrate that the mosaic ratio in the blood remained stable even after 3 years and has not changed over a longer period.

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.

HCN1 mutation spectrum: from neonatal epileptic encephalopathy to benign generalized epilepsy and beyond

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels control neuronal excitability and their dysfunction has been linked to epileptogenesis but few individuals with neurological disorders related to variants altering HCN channels have been reported so far. In 2014, we described five individuals with epileptic encephalopathy due to de novo HCN1 variants. To delineate HCN1-related disorders and investigate genotype-phenotype correlations further, we assembled a cohort of 33 unpublished patients with novel pathogenic or likely pathogenic variants: 19 probands carrying 14 different de novo mutations and four families with dominantly inherited variants segregating with epilepsy in 14 individuals, but not penetrant in six additional individuals. Sporadic patients had epilepsy with median onset at age 7 months and in 36% the first seizure occurred during a febrile illness. Overall, considering familial and sporadic patients, the predominant phenotypes were mild, including genetic generalized epilepsies and genetic epilepsy with febrile seizures plus (GEFS+) spectrum. About 20% manifested neonatal/infantile onset otherwise unclassified epileptic encephalopathy. The study also included eight patients with variants of unknown significance: one adopted patient had two HCN1 variants, four probands had intellectual disability without seizures, and three individuals had missense variants inherited from an asymptomatic parent. Of the 18 novel pathogenic missense variants identified, 12 were associated with severe phenotypes and clustered within or close to transmembrane domains, while variants segregating with milder phenotypes were located outside transmembrane domains, in the intracellular N- and C-terminal parts of the channel. Five recurrent variants were associated with similar phenotypes. Using whole-cell patch-clamp, we showed that the impact of 12 selected variants ranged from complete loss-of-function to significant shifts in activation kinetics and/or voltage dependence. Functional analysis of three different substitutions altering Gly391 revealed that these variants had different consequences on channel biophysical properties. The Gly391Asp variant, associated with the most severe, neonatal phenotype, also had the most severe impact on channel function. Molecular dynamics simulation on channel structure showed that homotetramers were not conducting ions because the permeation path was blocked by cation(s) strongly complexed to the Asp residue, whereas heterotetramers showed an instantaneous current component possibly linked to deformation of the channel pore. In conclusion, our results considerably expand the clinical spectrum related to HCN1 variants to include common generalized epilepsy phenotypes and further illustrate how HCN1 has a pivotal function in brain development and control of neuronal excitability.