Making sense of missense variants in TTN-related congenital myopathies.

Mutations in the sarcomeric protein titin, encoded by TTN, are emerging as a common cause of myopathies. The diagnosis of a TTN-related myopathy is, however, often not straightforward due to clinico-pathological overlap with other myopathies and the prevalence of TTN variants in control populations. Here, we present a combined clinico-pathological, genetic and biophysical approach to the diagnosis of TTN-related myopathies and the pathogenicity ascertainment of TTN missense variants. We identified 30 patients with a primary TTN-related congenital myopathy (CM) and two truncating variants, or one truncating and one missense TTN variant, or homozygous for one TTN missense variant. We found that TTN-related myopathies show considerable overlap with other myopathies but are strongly suggested by a combination of certain clinico-pathological features. Presentation was typically at birth with the clinical course characterized by variable progression of weakness, contractures, scoliosis and respiratory symptoms but sparing of extraocular muscles. Cardiac involvement depended on the variant position. Our biophysical analyses demonstrated that missense mutations associated with CMs are strongly destabilizing and exert their effect when expressed on a truncating background or in homozygosity. We hypothesise that destabilizing TTN missense mutations phenocopy truncating variants and are a key pathogenic feature of recessive titinopathies that might be amenable to therapeutic intervention.

New genotype-phenotype correlations in a large European cohort of patients with sarcoglycanopathy.

Sarcoglycanopathies comprise four subtypes of autosomal recessive limb-girdle muscular dystrophies (LGMDR3, LGMDR4, LGMDR5 and LGMDR6) that are caused, respectively, by mutations in the SGCA, SGCB, SGCG and SGCD genes. In 2016, several clinicians involved in the diagnosis, management and care of patients with LGMDR3-6 created a European Sarcoglycanopathy Consortium. The aim of the present study was to determine the clinical and genetic spectrum of a large cohort of patients with sarcoglycanopathy in Europe. This was an observational retrospective study. A total of 33 neuromuscular centres from 13 different European countries collected data of the genetically confirmed patients with sarcoglycanopathy followed-up at their centres. Demographic, genetic and clinical data were collected for this study. Data from 439 patients from 13 different countries were collected. Forty-three patients were not included in the analysis because of insufficient clinical information available. A total of 159 patients had a confirmed diagnosis of LGMDR3, 73 of LGMDR4, 157 of LGMDR5 and seven of LGMDR6. Patients with LGMDR3 had a later onset and slower progression of the disease. Cardiac involvement was most frequent in LGMDR4. Sixty per cent of LGMDR3 patients carried one of the following mutations, either in a homozygous or heterozygous state: c.229C>T, c.739G>A or c.850C>T. Similarly, the most common mutations in LMGDR5 patients were c.525delT or c.848G>A. In LGMDR4 patients the most frequent mutation was c.341C>T. We identified onset of symptoms before 10 years of age and residual protein expression lower than 30% as independent risk factors for losing ambulation before 18 years of age, in LGMDR3, LGMDR4 and LGMDR5 patients. This study reports clinical, genetic and protein data of a large European cohort of patients with sarcoglycanopathy. Improving our knowledge about these extremely rare autosomal recessive forms of LGMD was helped by a collaborative effort of neuromuscular centres across Europe. Our study provides important data on the genotype-phenotype correlation that is relevant for the design of natural history studies and upcoming interventional trials in sarcoglycanopathies.

Novel Nonsense Mutation in SLC39A13 Initially Presenting as Myopathy: Case Report and Review of the Literature.

Myopathies comprise a heterogeneous group of disorders characterized by variable phenotypes. The increasing use of next-generation sequencing allows identification of the causative genes in a much higher percentage of patients with hereditary muscle disorders and also illustrates a considerable degree of overlap with other clinical entities, including connective tissue disorders. Here, we present a 14-year-old German patient who was initially suspected to suffer from myopathy based on his clinical, radiological, and muscle biopsy findings. Exome sequencing revealed a novel homozygous nonsense mutation in the SLC39A13 gene, causative for spondylocheiro dysplastic Ehlers Danlos syndrome (SCD-EDS), suggesting a connective tissue disorder. Including our patient, only 9 affected individuals from 4 families have been described for SCD-EDS so far. The previously reported patients did not show obvious evidence of myopathy, suggesting a broader clinical presentation than originally suspected. We summarize herein the current knowledge on clinical features as well as pathophysiological pathways for this rare connective tissue disease and discuss the high degree of clinical overlap between myopathic and connective tissue disorders.

Frequency of SCA8, SCA10, SCA12, SCA36, FXTAS and C9orf72 repeat expansions in SCA patients negative for the most common SCA subtypes.

BACKGROUND: Spinocerebellar ataxia (SCA) subtypes are often caused by expansions in non-coding regions of genes like SCA8, SCA10, SCA12 and SCA36. Other ataxias are known to be associated with repeat expansions such as fragile X-associated tremor ataxia syndrome (FXTAS) or expansions in the C9orf72 gene. When no mutation has been identified in the aforementioned genes next-generation sequencing (NGS)-based diagnostics may also be applied. In order to define an optimal diagnostic strategy, more information about the frequency and phenotypic characteristics of rare repeat expansion disorders associated with ataxia should be at hand. METHODS: We analyzed a consecutive cohort of 440 German unrelated patients with symptoms of cerebellar ataxia, dysarthria and other unspecific symptoms who were referred to our center for SCA diagnostics. They showed alleles in the normal range for the most common SCA subtypes SCA1-3, SCA6, SCA7 and SCA17. These patients were screened for expansions causing SCA8, SCA10, SCA12, SCA36 and FXTAS as well as for the pathogenic hexanucleotide repeat in the C9orf72 gene. RESULTS: Expanded repeats for SCA10, SCA12 or SCA36 were not identified in the analyzed patients. Five patients showed expanded SCA8 CTA/CTG alleles with 92-129 repeats. One 51-year-old male with unclear dementia symptoms was diagnosed with a large GGGGCC repeat expansion in C9orf72. The analysis of the fragile X mental retardation 1 gene (FMR1) revealed one patient with a premutation (>50 CGG repeats) and seven patients with alleles in the grey zone (41 to 54 CGG repeats). CONCLUSIONS: Altogether five patients showed 92 or more SCA8 CTA/CTG combined repeats. Our results support the assumption that smaller FMR1 gene expansions could be associated with the risk of developing neurological signs. The results do not support genetic testing for C9orf72 expansion in ataxia patients.

Monozygotic twins with a new compound heterozygous SPG11 mutation and different disease expression.

BACKGROUND: A pair of monozygotic 22-year-old twins with complicated hereditary spastic paraplegia caused by a novel SPG11 mutation is described. METHODS: Genetic testing and thorough clinical examination, magnetic resonance imaging (MRI) and MR-spectroscopy were performed. RESULTS: The twins were compound heterozygous for a known frameshift as well as a novel splice site mutation in the SPG11 gene. Clinically the patients showed a similar spectrum of symptoms but different disease presentation. MRI studies including morphometry and regional microstructural analysis by diffusion tensor imaging (DTI) of the corpus callosum (CC) by 3T MRI revealed marked thinning and corresponding increases of radial diffusivity (RD) and apparent diffusion coefficient (ADC) and reduction of the fractional anisotropy (FA) as compared to controls in all CC sections, particularly in the anterior callosal body. There was marked mainly supratentorial white matter reduction and to a lesser extent grey matter reduction in both patients. Involvement of the cortico-spinal tracts was reflected by FA and RD alterations. The more strongly affected patient showed a higher degree of callosal microstructural damage and cervical cord atrophy. CONCLUSIONS: This study shows a similar symptom spectrum, but distinct clinical and imaging findings in monozygotic twins suffering from SPG 11, suggesting individual downstream genetic effects and/or non-genetic modifiers.

Genetic analysis of VCP and WASH complex genes in a German cohort of sporadic ALS-FTD patients.

Mutations of the human valosin-containing protein, p97 (VCP) and Wiskott-Aldrich syndrome protein and SCAR homolog (WASH) complex genes cause motor neuron and cognitive impairment disorders. Here, we analyzed a cohort of German patients with sporadic amyotrophic lateral sclerosis and frontotemporal lobar degeneration comorbidity (ALS/FTD) for VCP and WASH complex gene mutations. Next-generation panel sequencing of VCP, WASH1, FAM21C, CCDC53, SWIP, strumpellin, F-actin capping protein of muscle Z-line alfa 1 (CAPZA1), and CAPZB genes was performed in 43 sporadic ALS/FTD patients. Subsequent analyses included Sanger sequencing, in silico analyses, real-time PCR, and CCDC53 immunoblotting. We identified 1 patient with the heterozygous variant c.26C>T in CAPZA1, predicted to result in p.Ser9Leu, and a second with the heterozygous start codon variant c.2T>C in CCDC53. In silico analysis predicted structural changes in the N-terminus of CAPZα1, which may interfere with CAPZα:CAPZß dimerization. Though the translation initiation codon of CCDC53 is mutated, real-time PCR and immunoblotting did neither reveal any evidence for a CCDC53 haploinsufficiency nor for aberrant CCDC53 protein species. Moreover, a disease-causing C9orf72 repeat expansion mutation was later on identified in this patient. Thus, with the exception of a putatively pathogenic heterozygous c.26C>T CAPZA1 variant, our genetic analysis did not reveal mutations in VCP and the remaining WASH complex subunits.

Expanding the phenotype of BICD2 mutations toward skeletal muscle involvement.

OBJECTIVE: To expand the spectrum of bicaudal D, Drosophila, homologue 2 (BICD2) gene-related diseases, which so far includes autosomal dominant spinal muscular atrophy with lower extremity predominance 2 and hereditary spastic paraplegia due to mutations in the BICD2 gene. METHODS: We analyzed 2 independent German families with clinical, genetic, and muscle MRI studies. In both index patients, muscle histopathologic studies were performed. Transfection studies were carried out to analyze the functional consequences of the disease-causing mutations. RESULTS: We identified the mutations p.Ser107Leu and p.Thr703Met in the BICD2 gene in the 2 families, respectively. In contrast to other patients carrying the same mutations, our patients present features of a myopathy with slow progression. Immunofluorescence studies and immunoelectron microscopy showed striking impairment of Golgi integrity, vesicle pathology, and abnormal BICD2 accumulation either within the nuclei (p.Ser107Leu) or in the perinuclear region (p.Thr703Met). Transfection studies confirmed BICD2 aggregation in different subcellular locations. CONCLUSIONS: Our findings extend the phenotypic spectrum of BICD2-associated disorders by features of a chronic myopathy and show a pathomechanism of BICD2 defects in skeletal muscle.

A large deletion in RPGR causes XLPRA in Weimaraner dogs.

BACKGROUND: Progressive retinal atrophy (PRA) belongs to a group of inherited retinal disorders associated with gradual vision impairment due to degeneration of retinal photoreceptors in various dog breeds. PRA is highly heterogeneous, with autosomal dominant, recessive or X-linked modes of inheritance. In this study we used exome sequencing to investigate the molecular genetic basis of a new type of PRA, which occurred spontaneously in a litter of German short-hair Weimaraner dogs. RESULTS: Whole exome sequencing in two PRA-affected Weimaraner dogs identified a large deletion comprising the first four exons of the X-linked retinitis pigmentosa GTPase regulator (RPGR) gene known to be involved in human retinitis pigmentosa and canine PRA. Screening of 16 individuals in the corresponding pedigree of short-hair Weimaraners by qPCR, verified the deletion in hemizygous or heterozygous state in one male and six female dogs, respectively. The mutation was absent in 88 additional unrelated Weimaraners. The deletion was not detectable in the parents of one older female which transmitted the mutation to her offspring, indicating that the RPGR deletion represents a de novo mutation concerning only recent generations of the Weimaraner breed in Germany. CONCLUSION: Our results demonstrate the value of an existing DNA biobank combined with exome sequencing to identify the underlying genetic cause of a spontaneously occurring inherited disease. Identification of the genetic cause has allowed the development of a diagnostic test, which should help to eradicate the PRA causing mutation from the respective canine line. Thus, planning of future pairings is facilitated and manifestation of this type of PRA can be prevented.

A Novel ECM1 Splice Site Mutation in Lipoid Proteinosis: Case Report plus Review of the Literature.

Lipoid proteinosis (LP) is an autosomal recessive genodermatosis known to be caused by mutations in ECM1. Nonsense and missense mutations are the most common variations in LP. Up to date, only 6 splice site mutations have been observed. We report on a 26-year-old female LP patient from a Turkish consanguineous family carrying a novel homozygous splice site mutation in intron 8 of the ECM1 gene and summarize the current knowledge on ECM1 mutations and possible genotype-phenotype correlations.

WDR45 mutations in Rett (-like) syndrome and developmental delay: Case report and an appraisal of the literature.

Mutations in the WDR45 gene have been identified as causative for the only X-linked type of neurodegeneration with brain iron accumulation (NBIA), clinically characterized by global developmental delay in childhood, followed by a secondary neurological decline with parkinsonism and/or dementia in adolescence or early adulthood. Recent reports suggest that WDR45 mutations are associated with a broader phenotypic spectrum. We identified a novel splice site mutation (c.440-2 A > G) in a 5-year-old Argentinian patient with Rett-like syndrome, exhibiting developmental delay, microcephaly, seizures and stereotypic hand movements, and discuss this finding, together with a review of the literature. Additional patients with a clinical diagnosis of Rett (-like) syndrome were also found to carry WDR45 mutations before (or without) clinical decline or signs of iron accumulation by magnetic resonance imaging (MRI). This information indicates that WDR45 mutations should be added to the growing list of genetic alterations linked to Rett-like syndrome. Further, clinical symptoms associated with WDR45 mutations ranged from early-onset epileptic encephalopathy in a male patient with a deletion of WDR45 to only mild cognitive delay in a female patient, suggesting that analysis of this gene should be considered more often in patients with developmental delay, regardless of severity. The increasing use of next generation sequencing technologies as well as longitudinal follow-up of patients with an early diagnosis will help to gain additional insight into the phenotypic spectrum associated with WDR45 mutations.

Mutational analysis of the CYP7B1, PNPLA6 and C19orf12 genes in autosomal recessive hereditary spastic paraplegia.

The hereditary spastic paraplegias (HSPs) comprise a group of genetically heterogeneous neurodegenerative diseases. Here, we evaluated the spectrum and frequency of mutations in the CYP7B1, PNPLA6 and C19orf12 genes (causative for the subtypes SPG5A, SPG39 and SPG43, respectively) in a cohort of 63 unrelated HSP patients with suspected autosomal recessive inheritance. Two novel homozygous mutations (one frameshift and one missense mutation) were detected in CYP7B1 (SPG5A), while no disease-causing mutation was identified for SPG39 or SPG43.

Two novel nebulin variants in an adult patient with congenital nemaline myopathy.

Congenital myopathies are clinically and genetically heterogeneous disorders, which often remain genetically undiagnosed for many years. Here we present a 40-year old patient with an almost lifelong history of a congenital myopathy of unknown cause. Muscle biopsy in childhood revealed mild myopathic features and rods. Clinical examination on presentation at the age of 40 revealed a facial weakness, atrophy and weakness of the arm muscles and distal leg muscles with mild contractures of the foot flexors and the right elbow. Subsequently, the nebulin gene was identified as a putative candidate gene by linkage analyses, but sequence analysis only revealed one heterozygous splice site mutation in intron 73 (c.10872+1G>T). Therefore, "Next Generation Sequencing" was performed, which revealed a second pathogenic variant in exon 145 (c.21622A>C). Compound-heterozygous carrier status was confirmed via sequence analysis of the index patient's parents. Whole body muscle MRI showed a muscle involvement as previously described in nebulin-associated myopathies. Based on biopsy material, genetic analyses and muscle MRI, we identified two novel, compound-heterozygous variants in the nebulin gene after a 30 year clinical history, which cause a classical childhood type of nemaline myopathy.

Smaller caliber renal arteries are a novel feature of uromodulin-associated kidney disease.

Hyperuricemia is very common in industrialized countries and known to promote vascular smooth muscle cell proliferation. Juvenile hyperuricemia is a hallmark of uromodulin-associated kidney disease characterized by progressive interstitial renal fibrosis leading to end-stage renal disease within decades. Here we describe a member of a Polish-German family with a history of familial background of chronic kidney disease, hyperuricemia, and gout. This patient had hypertension because of bilateral small renal arteries, hyperuricemia, and chronic kidney disease. Clinical and molecular studies were subsequently performed in 39 family members, which included a physical examination, Duplex ultrasound of the kidneys, laboratory tests for renal function, and urine analysis. In eight family members contrast-enhanced renal artery imaging by computed tomography-angiography or magnetic resonance imaging was conducted and showed that bilateral non-arteriosclerotic small caliber renal arteries were associated with hyperuricemia and chronic kidney disease. Of the 26 family members who underwent genotyping, 11 possessed the P236R mutation (c.707C>G) of the uromodulin gene. All family members with a small caliber renal artery carried the uromodulin P236R mutation. Statistical analysis showed a strong correlation between reduced renal artery lumen and decreased estimated glomerular filtration rate. Thus, bilateral small caliber renal arteries are a new clinical phenotype associated with an uromodulin mutation.

Analysis of the C19orf12 and WDR45 genes in patients with neurodegeneration with brain iron accumulation.

BACKGROUND: Neurodegeneration with brain iron accumulation (NBIA) comprises a clinically and genetically heterogeneous group of diseases presenting with movement disorders and brain iron deposits. In addition to NBIA subtypes caused by mutations in PANK2 and PLA2G6, mutations in the C19orf12 gene were recently described as the third frequent cause of NBIA (called mitochondrial membrane protein-associated neurodegeneration, MPAN). Additionally, the X-linked gene WDR45 was found causative for a special subtype named static encephalopathy in childhood with neurodegeneration in adulthood (also called BPAN); however, analysis of this gene in a broader spectrum of NBIA has not been reported yet. METHODS: In a heterogeneous cohort of 69 patients with suspected NBIA that did not carry mutations in PANK2 and PLA2G6, the coding region of C19orf12 was evaluated by Sanger sequencing. The WDR45 gene was analyzed via high resolution melting and subsequent sequence analysis. RESULTS: Previously described homozygous C19orf12 mutations were found in 3/69 NBIA patients (4.3%). Analysis of the WDR45 gene revealed a novel heterozygous missense mutation in one female NBIA patient showing psychomotor retardation with secondary decline. CONCLUSIONS: C19orf12 mutations were confirmed in our heterogeneous NBIA cohort, while WDR45 mutations appear to be restricted to the subtype showing encephalopathy in childhood with neurodegeneration in adulthood.

LAMA2-related congenital muscular dystrophy complicated by West syndrome.

BACKGROUND: Mutations in the LAMA2 gene cause autosomal recessive laminin α2 related congenital muscular dystrophy. In patients with partial laminin α2 deficiency the phenotype is usually milder than in those with absent protein. Apart from the typical white matter abnormalities, there is an increased risk of cerebral complications such as epilepsy and mental retardation, despite a structurally normal brain. METHODS/RESULTS: We present a patient with primary partial laminin α2 deficiency due to a homozygous novel LAMA2 missense mutation who developed West syndrome in his first year of life. To our knowledge, this combination has not previously been reported. A 5 year-old boy exhibited global hypotonia with generalized muscle weakness from birth. At 8 months of age he presented infantile spasms and an EEG finding of hypsarrhythmia. Seizures were controlled in a few weeks with intramuscular synthetic ACTH, followed by valproic acid. Two years later antiepileptic medication was withdrawn. He achieved unsupported walking at the age of 4, but his cognitive status corresponded to a 2 year-old child. Epilepsy has not recurred and brain MRI showed the typical white matter abnormalities without associated neuronal migration defects. CONCLUSION: This report widens the clinical spectrum of cerebral manifestations related with mutations in LAMA2. The beginning of a severe epileptic encephalopathy modifies the natural history of the disease.

Exome Sequencing Reveals AGBL5 as Novel Candidate Gene and Additional Variants for Retinitis Pigmentosa in Five Turkish Families.

PURPOSE: Retinitis pigmentosa (RP) is the most common inherited retinal disease with high genetic heterogeneity and variable phenotypes. Characteristic symptoms include night blindness and progressive loss of visual field, leading to blindness. Mutations in >60 genes have been identified to date as causative for RP, and additional candidate genes are assumed. METHODS: To find the disease-causing mutations in the affected members of five Turkish families, we sequenced whole exomes using an Illumina platform. RESULTS: Among all candidate genes for retinal degeneration we found two previously known sequence variations: a 4 bp deletion in the RPGR gene (c.1662_1665delAGAA; p.Glu555Glyfs*14) and a recently described USH1-causing missense mutation in MYO7A (c.472G>A, p.Gly158Arg). Furthermore, a novel 1 bp deletion in the VCAN gene (c.5118delA; p.Ser1707Valfs*44) was detected as well as a large deletion in EYS, spanning ∼ 400kb and comprising exons 16-26 (p.fs*). In one family, exome analyses of two affected individuals revealed a homozygous missense mutation (c.883G>A; p.Asp295Asn) in the AGBL5 (Agbl5; CCP5) gene, previously not reported to be associated with RP. RNA and protein analyses showed expression in human retina, as well as in mouse retina, brain and testis. Furthermore, cDNA analyses indicate the existence of tissue-specific AGBL5 splice variations in humans. AGBL5/CCP5 immunoreactivity was also visualized in human and mouse retinae. CONCLUSION: Due to the characteristic RP phenotype in patients carrying the AGBL5 missense mutation we suggest this gene as a candidate for a new form of autosomal recessively inherited RP and recommend further investigation to confirm this hypothesis.

Point mutation frequency in the FMR1 gene as revealed by fragile X syndrome screening.

Fragile X syndrome (FXS) is a common cause of intellectual disability, developmental delay and autism spectrum disorders. This syndrome is due to a functional loss of the FMR1 gene product FMRP, and, in most cases, it is caused by CGG repeat expansion in the FMR1 promoter. Yet, also other FMR1 mutations may cause a FXS-like phenotype. Since standard molecular testing does not include the analysis of the FMR1 coding region, the prevalence of point mutations causing FXS is not well known. Here, high resolution melting (HRM) was used to screen for FMR1 gene mutations in 508 males with clinical signs of mental retardation and developmental delay, but without CGG and GCC repeat expansions in the FMR1 gene and AFF2 genes, respectively. Sequence variations were identified by HRM analysis and verified by direct DNA sequencing. Two novel missense mutations (p.Gly482Ser in one patient and p.Arg534His in two unrelated patients), one intronic and two 3'-untranslated region (UTR) variations were identified in the FMR1 gene. Missense mutations in the FMR1 gene might account for a considerable proportion of cases in male patients with FXS-related symptoms, such as those linked to mental retardation and developmental delay.

High creatine kinase levels and white matter changes: clinical and genetic spectrum of congenital muscular dystrophies with laminin alpha-2 deficiency.

Primary deficiency of laminin alpha-2 due to mutations in the LAMA2 gene accounts for 30% of all patients with congenital muscular dystrophy. Here, we present seven patients with partial or total laminin alpha-2 deficiency (MDC1A) with a wide clinical spectrum, ranging from ambulant patients to patients who were never able to stand or sit. We identified two pathogenic mutations in the LAMA2 gene in all patients except for one patient in whom only one mutation was found. Six of the mutations were previously undescribed. In some of the milder cases, laminin alpha-2 expression in the muscle biopsy was only slightly reduced. These findings emphasize that analysis of the LAMA2 gene might be necessary in patients with muscle weakness, cerebral white matter changes and high creatine kinase levels, even in the presence of laminin alpha-2 in the muscle biopsy.