A novel de novo FEM1C variant is linked to neurodevelopmental disorder with absent speech, pyramidal signs and limb ataxia.

The principal component of the protein homeostasis network is the ubiquitin-proteasome system. Ubiquitination is mediated by an enzymatic cascade involving, i.e. E3 ubiquitin ligases, many of which belong to the cullin-RING ligases family. Genetic defects in the ubiquitin-proteasome system components, including cullin-RING ligases, are known causes of neurodevelopmental disorders. Using exome sequencing to diagnose a pediatric patient with developmental delay, pyramidal signs and limb ataxia, we identified a de novo missense variant c.376G>C; p.(Asp126His) in the FEM1C gene encoding a cullin-RING ligase substrate receptor. This variant alters a conserved amino acid located within a highly constrained coding region and is predicted as pathogenic by most in silico tools. In addition, a de novo FEM1C mutation of the same residue p.(Asp126Val) was associated with an undiagnosed developmental disorder, and the relevant variant (FEM1CAsp126Ala) was found to be functionally compromised in vitro. Our computational analysis showed that FEM1CAsp126His hampers protein substrate binding. To further assess its pathogenicity, we used the nematode Caenorhabditis elegans. We found that the FEM-1Asp133His animals (expressing variant homologous to the FEM1C p.(Asp126Val)) had normal muscle architecture yet impaired mobility. Mutant worms were sensitive to the acetylcholinesterase inhibitor aldicarb but not levamisole (acetylcholine receptor agonist), showing that their disabled locomotion is caused by synaptic abnormalities and not muscle dysfunction. In conclusion, we provide the first evidence from an animal model suggesting that a mutation in the evolutionarily conserved FEM1C Asp126 position causes a neurodevelopmental disorder in humans.

Mosaic IL6ST variant inducing constitutive GP130 cytokine receptor signaling as a cause of neonatal onset immunodeficiency with autoinflammation and dysmorphy.

Interleukin-6 signal transducer (IL6ST) encodes the GP130 protein which transduces the proinflammatory signaling of the IL6 cytokine family through Janus kinase signal transducers and activators of transcription pathway (JAK/STAT) activation. Biallelic loss-of-function IL6ST variants cause autosomal recessive hyper-IgE syndrome or a variant of the Stuve-Wiedemann syndrome. Somatic gain-of-function IL6ST mutations, in particular, small monoallelic in-frame deletions of which the most prevalent is the IL6ST Ser187_Tyr190del, are an established cause of inflammatory hepatocellular tumors, but so far, no disease caused by such mutations present constitutively has been described. Herein, we report a pediatric proband with a novel syndrome of neonatal onset immunodeficiency with autoinflammation and dysmorphy associated with the IL6ST Tyr186_Tyr190del variant present constitutively. Tyr186_Tyr190del was found by exome sequencing and was shown to be de novo (absent in proband's parents and siblings) and mosaic (present in approximately 15-40% of cells depending on the tissue studied-blood, urine sediment, hair bulbs and buccal swab). Functional studies were performed in the Epstein-Barr virus-immortalized patient's B cell lymphoblastoid cell line, which carried the variant in approximately 95% of the cells. Western blot showed that the patient's cells exhibited constitutive hyperphosphorylation of Tyr705 in STAT3, which is indicative of IL6-independent activation of GP130. Interestingly, the STAT3 phosphorylation could be inhibited with ruxolitinib as well as tofacitinib, which are clinically approved JAK1 and JAK3 (to lesser extent JAK2 and JAK1) inhibitors, respectively. Given our results and the recent reports of ruxolitinib and tofacitinib use for the treatment of diseases caused by direct activation of STAT3 or STAT1, we speculate that these drugs may be effective in the treatment of our patient's condition.

Patients with Infections of The Central Nervous System Have Lowered Gut Microbiota Alpha Diversity.

There are multiple lines of evidence for the existence of communication between the central nervous system (CNS), gut, and intestinal microbiome. Despite extensive analysis conducted on various neurological disorders, the gut microbiome was not yet analyzed in neuroinfections. In the current study, we analyzed the gut microbiome in 47 consecutive patients hospitalized with neuroinfection (26 patients had viral encephalitis/meningitis; 8 patients had bacterial meningitis) and in 20 matched for age and gender health controls. Using the QIIME pipeline, 16S rRNA sequencing and classification into operational taxonomic units (OTUs) were performed on the earliest stool sample available. Bacterial taxa such as Clostridium, Anaerostipes, Lachnobacterium, Lachnospira, and Roseburia were decreased in patients with neuroinfection when compared to controls. Alpha diversity metrics showed lower within-sample diversity in patients with neuroinfections, though there were no differences in beta diversity. Furthermore, there was no significant change by short-term (1-3 days) antibiotic treatment on the gut microbiota, although alpha diversity metrics, such as Chao1 and Shannon's index, were close to being statistically significant. The cause of differences between patients with neuroinfections and controls is unclear and could be due to inflammation accompanying the disease; however, the effect of diet modification and/or hospitalization cannot be excluded.

Postzygotic mosaicism of a novel PTPN11 mutation in monozygotic twins discordant for metachondromatosis.

Genetic mosaicism caused by postzygotic mutations is of a great interest due to its role in human disease. Monozygotic twins arising from a single zygote are considered as genetically identical, and any differences likely to be caused by postzygotic events. Thus, phenotypically discordant monozygotic twins offer a unique opportunity to study genotype-phenotype correlation. Here, we present a three-generation family starting from a pair of monozygotic twins discordant for metachondromatosis due to postzygotic p.(Gln175His) variant in the PTPN11 gene. Both phenotypically discordant monozygotic twins harbor p.(Gln175His), however significant differences in mosaic ratio is observed not only between twins, but also within different tissue types within one individual. Phenotypic manifestation of p.(Gln175His) in examined family clearly depends on allele variant fraction (VAF). Individuals harboring constitutional mutation (VAF 50%) present typical metachondromatosis. Milder phenotype is observed in twin harboring high-level mosaicism in the tissue of ectodermal origin (VAF 45%), but not in a blood (VAF 5%). Finally, her twin sister harboring low-level mosaicism in blood (VAF 2%) and nonblood (VAF 12%) tissues is phenotypically normal. Our results provide insights into biological role of mosaicism in disease and further support the usefulness of nonblood tissues as an optimal source of DNA for the identification of postzygotic mutations in phenotypically discordant monozygotic twins.

De novo stop-loss variants in CLDN11 cause hypomyelinating leukodystrophy.

Claudin-11, a tight junction protein, is indispensable in the formation of the radial component of myelin. Here, we report de novo stop-loss variants in the gene encoding claudin-11, CLDN11, in three unrelated individuals presenting with an early-onset spastic movement disorder, expressive speech disorder and eye abnormalities including hypermetropia. Brain MRI showed a myelin deficit with a discrepancy between T1-weighted and T2-weighted images and some progress in myelination especially involving the central and peripheral white matter. Exome sequencing identified heterozygous stop-loss variants c.622T>C, p.(*208Glnext*39) in two individuals and c.622T>G, p.(*208Gluext*39) in one individual, all occurring de novo. At the RNA level, the variant c.622T>C did not lead to a loss of expression in fibroblasts, indicating this transcript is not subject to nonsense-mediated decay and most likely translated into an extended protein. Extended claudin-11 is predicted to form an alpha helix not incorporated into the cytoplasmic membrane, possibly perturbing its interaction with intracellular proteins. Our observations suggest that stop-loss variants in CLDN11 expand the genetically heterogeneous spectrum of hypomyelinating leukodystrophies.

Mucopolysaccharidosis-Plus Syndrome: Report on a Polish Patient with a Novel VPS33A Variant with Comparison with Other Described Patients.

Eleven patients from Yakutia with a new lysosomal disease assumed then as mucopolysaccharidosis-plus syndrome (MPS-PS) were reported by Gurinova et al. in 2014. Up to now, a total number of 39 patients have been reported; in all of them, the c.1492C>T (p.Arg498Trp) variant of the VPS33A gene was detected. Here, we describe the first Polish MPS-PS patient with a novel homozygous c.599G>C (p.Arg200Pro) VPS33A variant presenting over 12 years of follow-up with some novel clinical features, including fetal ascites (resolved spontaneously), recurrent joint effusion and peripheral edemas, normal growth, and visceral obesity. Functional analyses revealed a slight presence of chondroitin sulphate (only) in urine glycosaminoglycan electrophoresis, presence of sialooligosaccharides in urine by thin-layer chromatography, and normal results of lysosomal enzymes activity and lysosphingolipids concentration in dried blood spot. The comparison with other MPS-PS described cases was also provided. The presented description of the natural history of MPS-PS in our patient may broaden the spectrum of phenotypes in this disease.

NDUFB8 Mutations Cause Mitochondrial Complex I Deficiency in Individuals with Leigh-like Encephalomyopathy.

Respiratory chain complex I deficiency is the most frequently identified biochemical defect in childhood mitochondrial diseases. Clinical symptoms range from fatal infantile lactic acidosis to Leigh syndrome and other encephalomyopathies or cardiomyopathies. To date, disease-causing variants in genes coding for 27 complex I subunits, including 7 mitochondrial DNA genes, and in 11 genes encoding complex I assembly factors have been reported. Here, we describe rare biallelic variants in NDUFB8 encoding a complex I accessory subunit revealed by whole-exome sequencing in two individuals from two families. Both presented with a progressive course of disease with encephalo(cardio)myopathic features including muscular hypotonia, cardiac hypertrophy, respiratory failure, failure to thrive, and developmental delay. Blood lactate was elevated. Neuroimaging disclosed progressive changes in the basal ganglia and either brain stem or internal capsule. Biochemical analyses showed an isolated decrease in complex I enzymatic activity in muscle and fibroblasts. Complementation studies by expression of wild-type NDUFB8 in cells from affected individuals restored mitochondrial function, confirming NDUFB8 variants as the cause of complex I deficiency. Hereby we establish NDUFB8 as a relevant gene in childhood-onset mitochondrial disease.

Biallelic variants in TMEM222 cause a new autosomal recessive neurodevelopmental disorder.

PURPOSE: To elucidate the novel molecular cause in families with a new autosomal recessive neurodevelopmental disorder. METHODS: A combination of exome sequencing and gene matching tools was used to identify pathogenic variants in 17 individuals. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) and subcellular localization studies were used to characterize gene expression profile and localization. RESULTS: Biallelic variants in the TMEM222 gene were identified in 17 individuals from nine unrelated families, presenting with intellectual disability and variable other features, such as aggressive behavior, shy character, body tremors, decreased muscle mass in the lower extremities, and mild hypotonia. We found relatively high TMEM222 expression levels in the human brain, especially in the parietal and occipital cortex. Additionally, subcellular localization analysis in human neurons derived from induced pluripotent stem cells (iPSCs) revealed that TMEM222 localizes to early endosomes in the synapses of mature iPSC-derived neurons. CONCLUSION: Our findings support a role for TMEM222 in brain development and function and adds variants in the gene TMEM222 as a novel underlying cause of an autosomal recessive neurodevelopmental disorder.

A recurrent de novo variant supports KCNC2 involvement in the pathogenesis of developmental and epileptic encephalopathy.

Developmental and epileptic encephalopathies (DEE) are a heterogenous group of conditions characterized by the co-occurrence of epilepsy and intellectual/developmental disability. Despite several known DEE-related genes, including these encoding ion channels, still many cases remain without molecular diagnosis. Here, we present a 2-year-old girl with severe DEE in whom whole exome sequencing revealed de novo p.(Val471Leu) variant in the KCNC2 encoding Kv3.2, a voltage-gated potassium channel. To the best of our knowledge, this is the third DEE case due to KCNC2 mutation. Our clinical and molecular findings, particularly the recurrence of p.(Val471Leu) in patient with similar clinical phenotype, further support KCNC2 as a novel DEE-associated gene.

18-Year-old patient with Klinefelter syndrome (47, XXY) and complete androgen insensitivity syndrome (CAIS) - case report.

AIMS: The aims of the presented case report are to emphasize the importance of a proper diagnostics and treatment in the case of the coexistence of Klinefelter syndrome (KS, 47 XXY) and complete androgen insensitivity syndrome (CAIS). Since there is no causal treatment it is necessary to provide the patient with a good quality of life, including psychological and sexological support. MATERIALS AND METHODS: The presented case report is the retrospective analysis of the patient's medical history over the 3 years. RESULTS: At the age of 15, the patient was directed to genetic testing due to primary amenorrhea. The results of the patient showed an incorrect male karyotype with the SRY gene present (47, XXY). A molecular diagnostics revealed a very rare variant of the androgen receptor (AR) mutation responsible for tissue insensitivity to androgens. The detected mutation has not been described in the available databases so far. Following a diagnosis of the presence of Klinefelter syndrome (KS, 47 XXY) together with complete androgen insensitivity syndrome (CAIS), the patient underwent a bilateral gonadectomy. CONCLUSIONS: In women with KS and CAIS physiological reproduction and maintenance of normal sex, hormone levels are not possible. A gonadectomy is performed due to the risk of malignant testicular tumors.

Peritoneal dialysis in an adult patient with tetralogy of Fallot diagnosed with incomplete Alagille syndrome.

BACKGROUND: Alagille syndrome is an autosomal dominant disorder usually caused by pathogenic variants of the JAG1 gene. In the past, cholestasis was a condition sine qua non for diagnosis of the syndrome. However, recent advancements in genetic testing have revealed that clinical presentations vary from lack of symptoms, to multiorgan involvement. Tetralogy of Fallot, the most frequent complex congenital heart defect in Alagille Syndrome, very rarely leads to renal failure requiring dialysis - there are only single reports of such cases in the literature, with none of them in Alagille Syndrome. CASE PRESENTATION: A 41-year-old woman suffering from cyanosis, dyspnea and plethora was admitted to the hospital. The patient suffered from chronic kidney disease and tetralogy of Fallot and had been treated palliatively with Blalock-Taussig shunts in the past; at admission, only minimal flow through the left shunt was preserved. These symptoms, together with impaired mental status and dysmorphic facial features, led to extensive clinical and genetic testing including whole exome sequencing. A previously unknown missense variant c.587G > A within the JAG1 gene was identified. As there were no signs of cholestasis, and subclinical liver involvement was only suggested by elevated alkaline phosphatase levels, the patient was diagnosed with incomplete Alagille Syndrome. End-stage renal disease required introduction of renal replacement therapy. Continuous ambulatory peritoneal dialysis was chosen and the patient's quality of life significantly increased. However, after refusal of further treatment, the patient died at the age of 45. CONCLUSIONS: Tetralogy of Fallot should always urge clinicians to evaluate for Alagille Syndrome and offer patients early nephrological care. Although tetralogy of Fallot rarely leads to end-stage renal disease requiring dialysis, if treated palliatively and combined with renal dysplasia (typical of Alagille Syndrome), it can result in severe renal failure as in the presented case. There is no standard treatment for such cases, but based on our experience, peritoneal dialysis is worth consideration. Finally, clinical criteria for the diagnosis of Alagille Syndrome require revision. Previously, diagnosis was based on cholestasis - however, cardiovascular anomalies are found to be more prevalent. Furthermore, the criteria do not include renal impairment, which is also common.

Overinterpretation of high throughput sequencing data in medical genetics: first evidence against TMPRSS3/GJB2 digenic inheritance of hearing loss.

BACKGROUND: Hearing loss (HL) is the most common disability of human senses characterized by a great allelic heterogeneity. GJB2 and TMPRSS3 are two well-known HL genes typically underlying its monogenic form. Recently, TMPRSS3/GJB2 digenic inheritance has been proposed. As results of genetic testing can be easily overinterpreted, we aimed to verify the hypothesis. METHODS: From genetic database of HL patients with at least one TMPRSS3 pathogenic variants we have selected individuals with additional GJB2 pathogenic variants. All of the available family members were recruited for the study. Segregation analysis of the respective TMPRSS3 and GJB2 pathogenic variants was performed within the families. RESULTS: The strategy has allowed to identify four individuals who were double heterozygous for known pathogenic TMPRSS3 and GJB2 variants. Two individuals from different families had GJB2 c.35delG and TMPRSS3 c.208delC and in two other individuals from one family GJB2 c.35delG together with TMPRSS3 c.1343T>C variants were found. None of these subjects has ever reported hearing problems and their hearing status was normal. CONCLUSIONS: Our data provide evidence against TMPRSS3/GJB2 digenic inheritance of HL. As high throughput sequencing is increasingly used for genetic testing, particular caution should be taken to provide the patients with accurate genetic counseling.

Dominant ELOVL1 mutation causes neurological disorder with ichthyotic keratoderma, spasticity, hypomyelination and dysmorphic features.

BACKGROUND: Ichthyosis and neurological involvement occur in relatively few known Mendelian disorders caused by mutations in genes relevant both for epidermis and neural function. OBJECTIVES: To identify the cause of a similar phenotype of ichthyotic keratoderma, spasticity, mild hypomyelination (on MRI) and dysmorphic features (IKSHD) observed in two unrelated paediatric probands without family history of disease. METHODS: Whole exome sequencing was performed in both patients. The functional effect of prioritised variant in ELOVL1 (very-long-chain fatty acids (VLCFAs) elongase) was analysed by VLCFA profiling by gas chromatography-mass spectrometry in stably transfected HEK2932 cells and in cultured patient's fibroblasts. RESULTS: Probands shared novel heterozygous ELOVL1 p.Ser165Phe mutation (de novo in one family, while in the other family, father could not be tested). In transfected cells p.Ser165Phe: (1) reduced levels of FAs C24:0-C28:0 and C26:1 with the most pronounced effect for C26:0 (P=7.8×10-6 vs HEK293 cells with wild type (wt) construct, no difference vs naïve HEK293) and (2) increased levels of C20:0 and C22:0 (P=6.3×10-7, P=1.2×10-5, for C20:0 and C22:0, respectively, comparison vs HEK293 cells with wt construct; P=2.2×10-7, P=1.9×10-4, respectively, comparison vs naïve HEK293). In skin fibroblasts, there was decrease of C26:1 (P=0.014), C28:0 (P=0.001) and increase of C20:0 (P=0.033) in the patient versus controls. There was a strong correlation (r=0.92, P=0.008) between the FAs profile of patient's fibroblasts and that of p.Ser165Phe transfected HEK293 cells. Serum levels of C20:0-C26:0 FAs were normal, but the C24:0/C22:0 ratio was decreased. CONCLUSION: The ELOVL1 p.Ser165Phe mutation is a likely cause of IKSHD.

Human Pegivirus in Patients with Encephalitis of Unclear Etiology, Poland.

Human pegivirus (HPgV), previously called hepatitis G virus or GB virus C, is a lymphotropic virus with undefined pathology. Because many viruses from the family Flaviviridae, to which HPgV belongs, are neurotropic, we studied whether HPgV could infect the central nervous system. We tested serum and cerebrospinal fluid samples from 96 patients with a diagnosis of encephalitis for a variety of pathogens by molecular methods and serology; we also tested for autoantibodies against neuronal antigens. We found HPgV in serum and cerebrospinal fluid from 3 patients who had encephalitis of unclear origin; that is, all the markers that had been tested were negative. Single-strand confirmation polymorphism and next-generation sequencing analysis revealed differences between the serum and cerebrospinal fluid-derived viral sequences, which is compatible with the presence of a separate HPgV compartment in the central nervous system. It is unclear whether HPgV was directly responsible for encephalitis in these patients.

Next-generation sequencing analysis of new genotypes appearing during antiviral treatment of chronic hepatitis C reveals that these are selected from pre-existing minor strains.

Coinfection with more than one hepatitis C virus (HCV) genotype is common, but its dynamics, particularly during antiviral treatment, remain largely unknown. We employed next-generation sequencing (NGS) to analyse sequential serum and peripheral blood mononuclear cell (PBMC) samples in seven patients with transient presence or permanent genotype change during antiviral treatment with interferon and ribavirin. Specimens were collected right before the therapy initiation and at 2, 4, 6, 8, 12, 20, 24, 36, 44 and 48 weeks during treatment and 6 months after treatment ceased. A mixture of two different genotypes was detected in the pretreatment samples from five patients and the minor genotype constituted 0.02 to 38 %. A transient or permanent change of the predominant genotype was observed in six patients. In three cases genotype 3 was replaced as the predominant genotype by genotype 4, in two cases genotype 3 was replaced by genotype 1, and in one subject genotype 1 was replaced by genotype 4. The PBMC- and serum-derived sequences were frequently discordant with respect to genotype and/or genotype proportions. In conclusion, pre-existing minor HCV genotypes can be selected rapidly during antiviral treatment and become transiently or permanently predominant. In coinfections involving genotype 3, genotype 3 was eliminated first from both the serum and PBMC compartments. The PBMC- and serum-derived HCV sequences were frequently discordant with respect to genotype and/or genotype proportions, suggesting that they constitute separate compartments with their own dynamics.

Clinical and molecular characteristics of newly reported mitochondrial disease entity caused by biallelic PARS2 mutations.

Most of the 19 mitochondrial aminoacyl-tRNA synthetases (mt-aaRSs) involved in mitochondrial protein synthesis are already linked to specific entities, one of the exceptions being PARS2 mutations for which pathogenic significance is not finally validated. The aim of the study was to characterize the PARS2- related phenotype.Three siblings with biallelic PARS2 mutations presented from birth with infantile spasms, secondary microcephaly, and similar facial dysmorphy. Mental development was deeply impaired with speech absence and no eye contact. A dilated cardiomyopathy and multiorgan failure developed in childhood at the terminal stage, together with mitochondrial dysfunction triggered by valproate administration.Brain MRI showed progressive volume loss of the frontal lobes, both cortical and subcortical, with widening of the cortical sulci and frontal horns of the lateral ventricles. Hypoplasia of the corpus callosum and progressive demyelination were additional findings. Similar brain features were seen in three already reported PARS2 patients and seemed specific for this defect when compared with other mt-aaRSs defects (DARS2, EARS2, IARS2, and RARS2).Striking resemblance of the phenotype and Alpers-like brain MRI changes with predominance of frontal cerebral volume loss (FCVL-AS) in six patients from three families of different ethnicity with PARS2 mutations, justifies to distinguish the condition as a new disease entity.

A 23-year follow-up of a male with Hajdu-Cheney syndrome due to NOTCH2 mutation.

We present a natural history of a 32-year-old man with Hajdu-Cheney syndrome (HJCYS), because of the de novo truncating mutation in the exon 34 of NOTCH2 (c.6424-6427delTCTG, p.Ser2142ArgfsX4), who has been followed up for a period of 23 years (between 9 and 32 years). During follow-up, we observed abnormalities of vision, hearing, voice, and progression of craniofacial features in the form of skeletal dysplasia with affected skull, dentition, spine, limbs, fingers, and toes. Low bone mineral density and history of fragility fractures also suggested primary osteoporosis being a clinical manifestation. According to Stengel-Rutkowski, Schimanek, and Wernheimer (1984; Human Genetics, 6, 272-295), systematic data acquisition has been used for quantitative analysis of anthropological, radiographic, and clinical features at childhood, adolescence, and young adulthood separately. A detailed phenotype description together with the results of reanalysis of 14 reports so far published on patients with HJCYS and NOTCH2 mutation showed similar phenotype evolution with age. The spectrum of observed features may improve diagnostic tools for HJCYS at different periods of the lifespan.

Tinnitus in patients with hearing loss due to mitochondrial DNA pathogenic variants.

PURPOSE: Tinnitus described as individual perception of phantom sound constitutes a significant medical problem and has become an essential subject of many studies conducted worldwide. In the study, we aimed to examine the prevalence of tinnitus among Polish hearing loss (HL) patients with identified mitochondrial DNA (mtDNA) variants. METHODS: Among the selected group of unrelated HL patients with known mtDNA pathogenic variants, two questionnaires were conducted, i.e. Tinnitus Handicap Inventory translated into Polish (THI-POL) and Visual Analogue Scale (VAS) for measuring subjectively perceived tinnitus loudness, distress, annoyance and possibility of coping with this condition (VASs). Pathogenic mtDNA variants were detected with real-time PCR and sequencing of the whole mtDNA. RESULTS: This is the first extensive tinnitus characterization using THI-POL and VASs questionnaires in HL patients due to mtDNA variants. We have established the prevalence of tinnitus among the studied group at 23.5%. We found that there are no statistically significant differences in the prevalence of tinnitus and its characteristic features between HL patients with known HL mtDNA variants and the general Polish population. In Polish HL patients with tinnitus, m.7511T>C was significantly more frequent than in patients without tinnitus. We observed that the prevalence of tinnitus is lower in Polish patients with m.1555A>G as compared to other available data. CONCLUSIONS: Our data suggest that the mtDNA variants causative of HL may affect tinnitus development but this effect seems to be ethnic-specific.

Novel neuro-audiological findings and further evidence for TWNK involvement in Perrault syndrome.

BACKGROUND: Hearing loss and ovarian dysfunction are key features of Perrault syndrome (PRLTS) but the clinical and pathophysiological features of hearing impairment in PRLTS individuals have not been addressed. Mutations in one of five different genes HSD17B4, HARS2, LARS2, CLPP or TWNK (previous symbol C10orf2) cause the autosomal recessive disorder but they are found only in about half of the patients. METHODS: We report on two siblings with a clinical picture resembling a severe, neurological type of PRLTS. For an exhaustive characterisation of the phenotype neuroimaging with volumetric measurements and objective measures of cochlear hair cell and auditory nerve function (otoacustic emissions and auditory brainstem responses) were used. Whole exome sequencing was applied to identify the genetic cause of the disorder. Co-segregation of the detected mutations with the phenotype was confirmed by Sanger sequencing. In silico analysis including 3D protein structure modelling was used to predict the deleterious effects of the detected variants on protein function. RESULTS: We found two rare biallelic mutations in TWNK, encoding Twinkle, an essential mitochondrial helicase. Mutation c.1196A>G (p.Asn399Ser) recurred for the first time in a patient with PRLTS and the second mutation c.1802G>A (p.Arg601Gln) was novel for the disorder. In both patients neuroimaging studies showed diminished cervical enlargement of the spinal cord and for the first time in PRLTS partial atrophy of the vestibulocochlear nerves and decreased grey and increased white matter volumes of the cerebellum. Morphological changes in the auditory nerves, their desynchronized activity and partial cochlear dysfunction underlay the complex mechanism of hearing impairment in the patients. CONCLUSIONS: Our study unveils novel features on the phenotypic landscape of PRLTS and provides further evidence that the newly identified for PRLTS TWNK gene is involved in its pathogenesis.

Whole exome sequencing identifies TRIOBP pathogenic variants as a cause of post-lingual bilateral moderate-to-severe sensorineural hearing loss.

BACKGROUND: Implementation of whole exome sequencing has provided unique opportunity for a wide screening of causative variants in genetically heterogeneous diseases, including nonsyndromic hearing impairment. TRIOBP in the inner ear is responsible for proper structure and function of stereocilia and is necessary for sound transduction. METHODS: Whole exome sequencing followed by Sanger sequencing was conducted on patients derived from Polish hearing loss family. RESULTS: Based on whole exome analysis, we identified two TRIOBP pathogenic variants (c.802_805delCAGG, p.Gln268Leufs*610 and c.5014G>T, p.Gly1672*, the first of which was novel) causative of nonsyndromic, peri- to postlingual, moderate-to-severe hearing loss in three siblings from a Polish family. Typically, TRIOBP pathogenic variants lead to prelingual, severe-to-profound hearing loss, thus the onset and degree of hearing impairment in our patients represent a distinct phenotypic manifestation caused by TRIOBP variants. The pathogenic variant p.Gln268Leufs*610 disrupts the TRIOBP-4 and TRIOBP-5 isoforms (both expressed exclusively in the inner ear and retina) whereas the second pathogenic variant c.514G>T, p.Gly1672* affects only TRIOBP-5. CONCLUSIONS: The onset and degree of hearing impairment, characteristic for our patients, represent a unique phenotypic manifestation caused by TRIOBP pathogenic variants. Although TRIOBP alterations are not a frequent cause of hearing impairment, this gene should be thoroughly analyzed especially in patients with a postlingual hearing loss. A delayed onset of hearing impairment due to TRIOBP pathogenic variants creates a potential therapeutic window for future targeted therapies.