Complex structural variation and nonsense variant in trans cause VPS50-related disorder.

Homozygous VPS50 variants have been previously described in two unrelated patients with a neurodevelopmental disorder with microcephaly, seizures and neonatal cholestasis. VPS50 encodes a subunit that is unique to the heterotetrameric endosome-associated recycling protein (EARP) complex. The other subunits of the EARP complex, such as VPS51, VPS52 and VPS53, are also shared by the Golgi-associated retrograde protein complex. We report on an 18-month-old female patient with biallelic VPS50 variants. She carried a paternally inherited heterozygous nonsense c.13A>T; p.(Lys5*) variant. By long-read genome sequencing, we characterised a structural variant with a 4.3 Mb inversion flanked by deletions at both breakpoints on the maternal allele. The ~428 kb deletion at the telomeric inversion breakpoint encompasses the entire VPS50 gene. We demonstrated a deficiency of VPS50 in patient-derived fibroblasts, confirming the loss-of-function nature of both VPS50 variants. VPS53 and VPS52 protein levels were significantly reduced and absent, respectively, in fibroblasts of the patient. These data show that VPS50 and/or EARP deficiency and the associated functional defects underlie the phenotype in patients with VPS50 pathogenic variants. The VPS50-related core phenotype comprises severe developmental delay, postnatal microcephaly, hypoplastic corpus callosum, neonatal low gamma-glutamyl transpeptidase cholestasis and failure to thrive. The disease is potentially fatal in early childhood.

De novo variants in RNF213 are associated with a clinical spectrum ranging from Leigh syndrome to early-onset stroke.

PURPOSE: RNF213, encoding a giant E3 ubiquitin ligase, has been recognized for its role as a key susceptibility gene for moyamoya disease. Case reports have also implicated specific variants in RNF213 with an early-onset form of moyamoya disease with full penetrance. We aimed to expand the phenotypic spectrum of monogenic RNF213-related disease and to evaluate genotype-phenotype correlations. METHODS: Patients were identified through reanalysis of exome sequencing data of an unselected cohort of unsolved pediatric cases and through GeneMatcher or ClinVar. Functional characterization was done by proteomics analysis and oxidative phosphorylation enzyme activities using patient-derived fibroblasts. RESULTS: We identified 14 individuals from 13 unrelated families with (de novo) missense variants in RNF213 clustering within or around the Really Interesting New Gene (RING) domain. Individuals presented either with early-onset stroke (n = 11) or with Leigh syndrome (n = 3). No genotype-phenotype correlation could be established. Proteomics using patient-derived fibroblasts revealed no significant differences between clinical subgroups. 3D modeling revealed a clustering of missense variants in the tertiary structure of RNF213 potentially affecting zinc-binding suggesting a gain-of-function or dominant negative effect. CONCLUSION: De novo missense variants in RNF213 clustering in the E3 RING or other regions affecting zinc-binding lead to an early-onset syndrome characterized by stroke or Leigh syndrome.

Genetic landscape of congenital insensitivity to pain and hereditary sensory and autonomic neuropathies.

Congenital insensitivity to pain (CIP) and hereditary sensory and autonomic neuropathies (HSAN) are clinically and genetically heterogeneous disorders exclusively or predominantly affecting the sensory and autonomic neurons. Due to the rarity of the diseases and findings based mainly on single case reports or small case series, knowledge about these disorders is limited. Here, we describe the molecular workup of a large international cohort of CIP/HSAN patients including patients from normally under-represented countries. We identify 80 previously unreported pathogenic or likely pathogenic variants in a total of 73 families in the >20 known CIP/HSAN-associated genes. The data expand the spectrum of disease-relevant alterations in CIP/HSAN, including novel variants in previously rarely recognized entities such as ATL3-, FLVCR1- and NGF-associated neuropathies and previously under-recognized mutation types such as larger deletions. In silico predictions, heterologous expression studies, segregation analyses and metabolic tests helped to overcome limitations of current variant classification schemes that often fail to categorize a variant as disease-related or benign. The study sheds light on the genetic causes and disease-relevant changes within individual genes in CIP/HSAN. This is becoming increasingly important with emerging clinical trials investigating subtype or gene-specific treatment strategies.

Loss of supervillin causes myopathy with myofibrillar disorganization and autophagic vacuoles.

The muscle specific isoform of the supervillin protein (SV2), encoded by the SVIL gene, is a large sarcolemmal myosin II- and F-actin-binding protein. Supervillin (SV2) binds and co-localizes with costameric dystrophin and binds nebulin, potentially attaching the sarcolemma to myofibrillar Z-lines. Despite its important role in muscle cell physiology suggested by various in vitro studies, there are so far no reports of any human disease caused by SVIL mutations. We here report four patients from two unrelated, consanguineous families with a childhood/adolescence onset of a myopathy associated with homozygous loss-of-function mutations in SVIL. Wide neck, anteverted shoulders and prominent trapezius muscles together with variable contractures were characteristic features. All patients showed increased levels of serum creatine kinase but no or minor muscle weakness. Mild cardiac manifestations were observed. Muscle biopsies showed complete loss of large supervillin isoforms in muscle fibres by western blot and immunohistochemical analyses. Light and electron microscopic investigations revealed a structural myopathy with numerous lobulated muscle fibres and considerable myofibrillar alterations with a coarse and irregular intermyofibrillar network. Autophagic vacuoles, as well as frequent and extensive deposits of lipoproteins, including immature lipofuscin, were observed. Several sarcolemma-associated proteins, including dystrophin and sarcoglycans, were partially mis-localized. The results demonstrate the importance of the supervillin (SV2) protein for the structural integrity of muscle fibres in humans and show that recessive loss-of-function mutations in SVIL cause a distinctive and novel myopathy.

Inherited cases of CNOT3-associated intellectual developmental disorder with speech delay, autism, and dysmorphic facies.

De novo pathogenic variants in CNOT3 have recently been reported in a developmental delay disorder (intellectual developmental disorder with speech delay, autism, and dysmorphic facies [IDDSADF, OMIM: #618672]). The patients present with a variable degree of developmental delay and behavioral problems. To date, all reported disease-causing variants occurred de novo and no parent-child transmission was observed. We report for the first time autosomal dominant transmissions of the CNOT3-associated developmental disorder in two unrelated families. The clinical characteristics in our patients match the IDDSADF features reported so far and suggest substantial variability of the phenotype within the same family.

Male infant with paternal uniparental diploidy mosaicism and a 46,XX/46,XY karyotype.

A male patient with mosaic paternal uniparental diploidy (PUD) is presented. After birth, the patient presented with hypoglycemia, hemihypertrophy, umbilical hernia, and hepatomegaly. Afterward pancreatic hypertrophy, liver hemangiomas, and cysts were detected sonographically. At the age of 3.5 months, hepatoblastoma was diagnosed. To investigate suspected Beckwith-Wiedemann syndrome (BWS), extensive genetic analyses were performed using DNA from chorionic villus sampling, amniocentesis, and peripheral blood lymphocytes (chromosome analysis, methylation-specific multiplex ligation-dependent probe amplification assays, microsatellite analyses, and single nucleotide polymorphism array analysis). These analyses led to the detection of mosaic PUD. In peripheral blood lymphocytes, a male cell line (46,XY[27]/46,XX[5]) predominated, suggesting a mixture of uniparental isodisomy and heterodisomy. The genetic analyses suggest that the mosaic PUD status was attributable to fertilization of an oocyte by two sperms, with subsequent triploidy rescue giving rise to haploidy, which in turn was rescued. Notably, in the majority of the 28 mosaic PUD patients reported to date, BWS was initially suspected. Mosaic PUD status is associated with a higher risk for a broad range of malignant and benign tumors than in BWS. As tumors can also occur after childhood surveillance into adolescence is indicated. Mosaic PUD must therefore be considered in patients with suspected BWS.

Next generation sequencing and imprinting disorders: Current applications and future perspectives: Lessons from Silver-Russell syndrome.

Imprinting Disorders are a group of rare diseases with overlapping phenotypes which are associated with similar molecular changes and affect imprinted chromosomal regions. Clinical features mainly occur prenatally or in childhood, but have a severe lifelong impact on health. Due to their clinical and molecular heterogeneity, the diagnosis of imprinting disorders is often challenging and requires testing of a broad spectrum of genomic variants and aberrant methylation of imprinted loci (epimutations). A significant number of patients suspicious for imprinting disorders remain without a molecular confirmation, and in these cases differential diagnoses have to be considered. In fact, in patients with clinical features suggestive for imprinting disorders, the precise identification of the molecular cause is relevant for both clinical management as well as for genetic counselling. Thus, a comprehensive testing approach has to be applied. Next generation sequencing (NGS) based studies show that this technique is a valuable tool to improve the diagnostic efficiency particularly in entities with broad differential diagnoses. Furthermore, the development of diverse NGS approaches allows new insights in the function of imprinted regions, their structures, interactions and regulation. Based on a large cohort of patients referred for routine Silver Russel syndrome testing, the appropriateness and limitations of first trial tests in imprinting disorders are demonstrated in this report, but the chances of genomic NGS approaches for diagnostics and research are elucidated as well. Finally, the significance of the precise molecular diagnosis for the personalized management of the patient, and genetic counselling of the family will be discussed.

Maternal variants in NLRP and other maternal effect proteins are associated with multilocus imprinting disturbance in offspring.

BACKGROUND: Genomic imprinting results from the resistance of germline epigenetic marks to reprogramming in the early embryo for a small number of mammalian genes. Genetic, epigenetic or environmental insults that prevent imprints from evading reprogramming may result in imprinting disorders, which impact growth, development, behaviour and metabolism. We aimed to identify genetic defects causing imprinting disorders by whole-exome sequencing in families with one or more members affected by multilocus imprinting disturbance. METHODS: Whole-exome sequencing was performed in 38 pedigrees where probands had multilocus imprinting disturbance, in five of whom maternal variants in NLRP5 have previously been found. RESULTS: We now report 15 further pedigrees in which offspring had disturbance of imprinting, while their mothers had rare, predicted-deleterious variants in maternal effect genes, including NLRP2, NLRP7 and PADI6. As well as clinical features of well-recognised imprinting disorders, some offspring had additional features including developmental delay, behavioural problems and discordant monozygotic twinning, while some mothers had reproductive problems including pregnancy loss. CONCLUSION: The identification of 20 putative maternal effect variants in 38 families affected by multilocus imprinting disorders adds to the evidence that maternal genetic factors affect oocyte fitness and thus offspring development. Testing for maternal-effect genetic variants should be considered in families affected by atypical imprinting disorders.

Paternally Inherited IGF2 Mutation and Growth Restriction.

In humans, mutations in IGF1 or IGF1R cause intrauterine and postnatal growth restriction; however, data on mutations in IGF2, encoding insulin-like growth factor (IGF) II, are lacking. We report an IGF2 variant (c.191C→A, p.Ser64Ter) with evidence of pathogenicity in a multigenerational family with four members who have growth restriction. The phenotype affects only family members who have inherited the variant through paternal transmission, a finding that is consistent with the maternal imprinting status of IGF2. The severe growth restriction in affected family members suggests that IGF-II affects postnatal growth in addition to prenatal growth. Furthermore, the dysmorphic features of affected family members are consistent with a role of deficient IGF-II levels in the cause of the Silver-Russell syndrome. (Funded by Bundesministerium für Bildung und Forschung and the European Union.).

NLRP genes and their role in preeclampsia and multi-locus imprinting disorders.

Preeclampsia (PE) affects 2-5% of all pregnancies. It is a multifactorial disease, but it has been estimated that 35% of the variance in liability of PE are attributable to maternal genetic effects and 20% to fetal genetic effects. PE has also been reported in women delivering children with Beckwith-Wiedemann syndrome (BWS, OMIM 130650), a disorder associated with aberrant methylation at genomically imprinted loci. Among others, members of the NLRP gene family are involved in the etiology of imprinting defects. Thus, a functional link between PE, NLRP gene mutations and aberrant imprinting can be assumed. Therefore we analyzed a cohort of 47 PE patients for NLRP gene mutations by next generation sequencing. In 25 fetuses where DNA was available we determined the methylation status at the imprinted locus. With the exception of one woman heterozygous for a missense variant in the NLRP7 gene (NM_001127255.1(NLRP7):c.542G>C) we could not identify further carriers, in the fetal DNA normal methylation patterns were observed. Thus, our negative screening results in a well-defined cohort indicate that NLRP mutations are not a relevant cause of PE, though strong evidence for a functional link between NLRP mutations, PE and aberrant methylation exist.

Targeted Next Generation Sequencing Approach in Patients Referred for Silver-Russell Syndrome Testing Increases the Mutation Detection Rate and Provides Decisive Information for Clinical Management.

OBJECTIVE: To investigate the contribution of differential diagnoses to the mutation spectrum of patients referred for Silver-Russell syndrome (SRS) testing. STUDY DESIGN: Forty-seven patients referred for molecular testing for SRS were examined after exclusion of one of the SRS-associated alterations. After clinical classification, a targeted next generation sequencing approach comprising 25 genes associated with other diagnoses or postulated as SRS candidate genes was performed. RESULTS: By applying the Netchine-Harbinson clinical scoring system, indication for molecular testing for SRS was confirmed in 15 out of 47 patients. In 4 out of these 15 patients, disease-causing variants were found in genes associated with other diagnoses. These patients carried mutations associated with Bloom syndrome, Mulibrey nanism, KBG syndrome, or IGF1R-associated short stature. We could not detect any pathogenic mutation in patients with a negative clinical score. CONCLUSIONS: Some of the differential diagnoses detected in the cohort presented here have a major impact on clinical management. Therefore, we emphasize that the molecular defects associated with these clinical pictures should be excluded before the clinical diagnosis "SRS" is made. Finally, we could show that a broad molecular approach including the differential diagnoses of SRS increases the detection rate.

Examinations of maternal uniparental disomy and epimutations for chromosomes 6, 14, 16 and 20 in Silver-Russell syndrome-like phenotypes.

BACKGROUND: Silver-Russell syndrome (SRS) is a growth retardation disorder with a very broad molecular and clinical spectrum. Whereas the association of SRS with imprinting disturbances of chromosomes 11p15.5 and 7 is generally accepted, there are controversial discussions on the involvement of other molecular changes. The recent reports on the occurrence of maternal uniparental disomies of chromosomes 6, 16 and 20 (upd(6, 16, 20)mat), as well as 14q32 imprint alterations in patients with SRS phenotypes raise the question on the involvement of these mutations in the etiology of SRS. METHODS: A cohort of 54 growth retarded patients with SRS features was screened for aberrant methylation patterns of chromsomes 6, 14, 16 and 20. RESULTS: One carrier of a 14q32 epimutation was identified whereas epimutations and maternal UPD for chromosomes 6, 16 and 20 were excluded. CONCLUSIONS: Our data and those from the literature confirm that 14q32 disturbances significantly contribute to the mutation spectrum in this cohort. Furthermore, maternal uniparental disomy of chromosomes 6, 16 and 20 can be observed, but are rare. In case they occur they can be regarded as causative for clinical features.

Microdeletions of the 7q32.2 imprinted region are associated with Silver-Russell syndrome features.

The association of maternal uniparental disomy of human chromosome 7 (upd(7) mat) and the growth retardation disorder Silver-Russell syndrome (SRS) is well established, but the causative gene or region is currently unknown. However, several observations indicate that molecular alterations of the genomically imprinted MEST region in 7q32.2 are associated with growth retardation and a phenotype reminiscent to SRS. We now report on a second patient with a similar phenotype and a de novo 7q32.2 microdeletion including MEST affecting the paternal allele. This confirms the central role of imprinted genes in 7q32.2 in the etiology of a growth retardation phenotype associated with SRS features.

Congenital imprinting disorders: Application of multilocus and high throughput methods to decipher new pathomechanisms and improve their management.

Imprinting disorders (IDs) are a group of congenital diseases affecting growth, development and metabolism. They are caused by changes in the allele-specific regulation ("epigenetic mutation") or in the genomic sequence ("genetic mutation") of imprinted genes. Currently molecular tests in ID patients are generally restricted to single loci classically associated with the disease, but this approach limits diagnostic yield, because of the molecular and clinical heterogeneity between IDs. From the technical point of view, these limitations are aggravated by the lack of standardization in testing methodology, in the DNA sequences tested, and in clinical inclusion criteria prompting testing. However, an increasing number of new studies show that these problems can be addressed by the use of new tests targeting multiple loci and/or a total exome and genome analysis. The rapid development of efficient and high-throughput molecular techniques and their applications in research and diagnostics in the last decade have led to an impressive increase of knowledge on IDs and their basic pathomechanisms. In combination with the improvement of data recording and documentation, the diagnostic strategies are increasingly based on standardized protocols, and thereby provide the backbone for directed counseling, more personalized management, and new therapeutic approaches.

Bi-allelic variants in CELSR3 are implicated in central nervous system and urinary tract anomalies.

CELSR3 codes for a planar cell polarity protein. We describe twelve affected individuals from eleven independent families with bi-allelic variants in CELSR3. Affected individuals presented with an overlapping phenotypic spectrum comprising central nervous system (CNS) anomalies (7/12), combined CNS anomalies and congenital anomalies of the kidneys and urinary tract (CAKUT) (3/12) and CAKUT only (2/12). Computational simulation of the 3D protein structure suggests the position of the identified variants to be implicated in penetrance and phenotype expression. CELSR3 immunolocalization in human embryonic urinary tract and transient suppression and rescue experiments of Celsr3 in fluorescent zebrafish reporter lines further support an embryonic role of CELSR3 in CNS and urinary tract formation.

Clinical significance of copy number variations in the 11p15.5 imprinting control regions: new cases and review of the literature.

Among the clusters of imprinted genes in humans, one of the most relevant regions involved in human growth is localised in 11p15. Opposite epigenetic and genomic disturbances in this chromosomal region contribute to two distinct imprinting disorders associated with disturbed growth, Silver-Russell and Beckwith-Wiedemann syndromes. Due to the complexity of the 11p15 imprinting regions and their interactions, the interpretation of the copy number variations in that region is complicated. The clinical outcome in case of microduplications or microdeletions is therefore influenced by the size, the breakpoint positions and the parental inheritance of the imbalance as well as by the imprinting status of the affected genes. Based on their own new cases and those from the literature, the authors give an overview on the genotype-phenotype correlation in chromosomal rearrangements in 11p15 as the basis for a directed genetic counselling. The detailed characterisation of patients and families helps to further delineate risk figures for syndromes associated with 11p15 disturbances. Furthermore, these cases provide us with profound insights in the complex regulation of the (imprinted) factors localised in 11p15.

Variant of the catalytic cysteine of UFSP2 leads to spondyloepimetaphyseal dysplasia type Di Rocco.

Spondyloepimetaphyseal dysplasia (SEMD) is characterized by vertebral, epiphyseal, and metaphyseal alterations. Patients become predominantly apparent with disproportionate short stature. The genetic background of SEMD is heterogeneous, with different modes of inheritance (autosomal dominant, autosomal recessive, and X-linked disorders). Amongst the genes in which variants are known to cause SEMD, UFM1-specific protease 2 (UFSP2) encodes a cysteine protease involved in the maturation of Ubiquitin-fold modifier 1 (UFM1). Heterozygous pathogenic variants affecting the C-terminal catalytic domain of UFSP2 are related to two entities of skeletal dysplasia, Beukes hip dysplasia (BHD) and SEMD type Di Rocco (SEMDDR). This is the first report of a de novo heterozygous variant affecting the catalytic Cys302 residue of UFSP2 (NM_018359.3:c.905G>C, p.(Cys302Ser)) causing SEMDDR. According to previously described patients with SEMDDR, our patient presented with disproportionate short stature, genu varum, gait instability, and radiologically detected epiphyseal and metaphyseal alterations. Additionally, a bell-shaped thorax, lumbar hyperlordosis, muscular hypotonia, and coxa vara were observed in the patient described in this study. Our findings underline the fundamental importance of an intact catalytic triad of the human UFSP2 for normal skeletal development and extend the phenotypical features of patients with UFSP2-related skeletal dysplasia.

Molecular characterisation of 36 multilocus imprinting disturbance (MLID) patients: a comprehensive approach.

BACKGROUND: Imprinting disorders (ImpDis) comprise diseases which are caused by aberrant regulation of monoallelically and parent-of-origin-dependent expressed genes. A characteristic molecular change in ImpDis patients is aberrant methylation signatures at disease-specific loci, without an obvious DNA change at the specific differentially methylated region (DMR). However, there is a growing number of reports on multilocus imprinting disturbances (MLIDs), i.e. aberrant methylation at different DMRs in the same patient. These MLIDs account for a significant number of patients with specific ImpDis, and several reports indicate a central role of pathogenic maternal effect variants in their aetiology by affecting the maturation of the oocyte and the early embryo. Though several studies on the prevalence and the molecular causes of MLID have been conducted, homogeneous datasets comprising both genomic and methylation data are still lacking. RESULTS: Based on a cohort of 36 MLID patients, we here present both methylation data obtained from next-generation sequencing (NGS, ImprintSeq) approaches and whole-exome sequencing (WES). The compilation of methylation data did not reveal a disease-specific MLID episignature, and a predisposition for the phenotypic modification was not obvious as well. In fact, this lack of epigenotype-phenotype correlation might be related to the mosaic distribution of imprinting defects and their functional relevance in specific tissues. CONCLUSIONS: Due to the higher sensitivity of NGS-based approaches, we suggest that ImprintSeq might be offered at reference centres in case of ImpDis patients with unusual phenotypes but MLID negative by conventional tests. By WES, additional MLID causes than the already known maternal effect variants could not be identified, neither in the patients nor in the maternal exomes. In cases with negative WES results, it is currently unclear to what extent either environmental factors or undetected genetic variants contribute to MLID.

Imprinting disorders.

Imprinting disorders (ImpDis) are congenital conditions that are characterized by disturbances of genomic imprinting. The most common individual ImpDis are Prader-Willi syndrome, Angelman syndrome and Beckwith-Wiedemann syndrome. Individual ImpDis have similar clinical features, such as growth disturbances and developmental delay, but the disorders are heterogeneous and the key clinical manifestations are often non-specific, rendering diagnosis difficult. Four types of genomic and imprinting defect (ImpDef) affecting differentially methylated regions (DMRs) can cause ImpDis. These defects affect the monoallelic and parent-of-origin-specific expression of imprinted genes. The regulation within DMRs as well as their functional consequences are mainly unknown, but functional cross-talk between imprinted genes and functional pathways has been identified, giving insight into the pathophysiology of ImpDefs. Treatment of ImpDis is symptomatic. Targeted therapies are lacking owing to the rarity of these disorders; however, personalized treatments are in development. Understanding the underlying mechanisms of ImpDis, and improving diagnosis and treatment of these disorders, requires a multidisciplinary approach with input from patient representatives.

Quality assurance within the context of genome diagnostics (a german perspective).

The rapid and dynamic implementation of Next-Generation Sequencing (NGS)-based assays has revolutionized genetic testing, and in the near future, nearly all molecular alterations of the human genome will be diagnosable via massive parallel sequencing. While this progress will further corroborate the central role of human genetics in the multidisciplinary management of patients with genetic disorders, it must be accompanied by quality assurance measures in order to allow the safe and optimal use of knowledge ascertained from genome diagnostics. To achieve this, several valuable tools and guidelines have been developed to support the quality of genome diagnostics. In this paper, authors with experience in diverse aspects of genomic analysis summarize the current status of quality assurance in genome diagnostics, with the aim of facilitating further standardization and quality improvement in one of the core competencies of the field.