Heterozygosity for loss-of-function variants in LZTR1 is associated with isolated multiple café-au-lait macules.

PURPOSE: Pathogenic LZTR1 variants cause schwannomatosis and dominant/recessive Noonan syndrome (NS). We aim to establish an association between heterozygous loss-of-function (LoF) LZTR1 alleles and isolated multiple café-au-lait macules (CaLMs). METHODS: 849 unrelated participants with multiple CaLMs, lacking pathogenic/likely pathogenic NF1 and SPRED1 variants, underwent RASopathy gene panel sequencing. Data on 125 individuals with heterozygous LZTR1 variants were collected for characterizing their clinical features and the associated molecular spectrum. In vitro functional assessment was performed on a representative panel of missense variants and small in-frame deletions. RESULTS: Analysis revealed heterozygous LZTR1 variants in 6.0% (51/849) of participants, exceeding the general population prevalence. LZTR1-related CaLMs varied in number, displayed sharp or irregular borders, and were generally isolated, but occasionally associated with features recurring in RASopathies. In two families, CaLMs and schwannomas co-occurred. The molecular spectrum mainly consisted of truncating variants, indicating LoF. These variants substantially overlapped with those occurring in schwannomatosis and recessive NS. Functional characterization showed accelerated protein degradation or mislocalization, and failure to downregulate MAPK signaling. CONCLUSION: Our findings expand the phenotypic variability associated with LZTR1 variants, which, in addition to conferring susceptibility to schwannomatosis and causing dominant and recessive NS, occur in individuals with isolated multiple CaLMs.

Prenatal diagnosis of Noonan syndrome in a set of monozygotic twins- a case report.

BACKGROUND: We report a pair of dichorionic diamniotic (DCDA) twin pregnancy affected by Noonan syndrome (NS) with a novel mutation of LZTR1 determined by genetic analysis. CASE PRESENTATION: A pregnant woman with monozygotic twins (DCDA) at 12 + 2 weeks gestation was referred to our center. This was her second pregnancy following a previous delivery of a healthy infant. Nuchal translucency of two fetuses was 11.2 mm (CRL 62.0 mm) and 6.9 mm (CRL 62.1 mm) respectively. Ultrasound examination indicated cystic hygroma and hypoplastic ear. The couple was not consanguineous, and both had normal phenotype. Familial hereditary disease was also excluded. Under ultrasound guidance, 30 mg of chorionic villi was obtained for karyotyping, quantitative fluorescent polymerase chain reaction (QF-PCR), chromosomal microarray analysis(CMA), and Trio-whole-exome sequencing(WES) examination. We used the "target region capture and sequencing" for WES, and the BWA (Burrows Wheeler Aligner) Multi-Vision software package for the data analysis. The results of all these tests were normal except WES detected a c.427 A > G mutation in the exonic region of the LZTR1 gene and a p. Asn143Asp novel heterozygous mutation associated with NS in this pair of twins. In addition, WES suggested that the mutation in the twin fetuses originated from the mother. When the mother got the genetic test report, she came to our fetal medicine department for genetic counseling and she declined the appointment with a clinical geneticist. The couple opted to terminate the pregnancy. Because the patient did not choose to terminate the pregnancy at our hospital, we were unable to take further examination. With the help of colleagues in another hospital, photos of the fetuses were taken. Compared with the prenatal ultrasound results, the appearance of the "cystic hygroma" and "hypoplastic ear" was consistent with the ultrasound. The couple were depressed after knowing this pathogenic result and although we advised the mother to take further investigation, they refused. CONCLUSION: The mutant locus might be incompletely dominant, which led to an abnormal fetal phenotype such as cystic hygroma and hypoplastic ear.

Comparison of the frequency of loss-of-function LZTR1 variants between schwannomatosis patients and the general population.

Schwannomatosis is a rare tumor predisposition syndrome that causes multiple schwannomas. Germline loss-of-function (LoF) LZTR1 variants were only recently identified as disease-causing, so relatively few variants have been identified in patients. In addition, many LoF variants exist in Genome Aggregation Database (gnomAD) in people who do not have clinical symptoms of schwannomatosis. These factors, and the incomplete penetrance seen in this condition, hinder definitive interpretation of the clinical significance of novel LoF variants identified in schwannomatosis patients. We collated published LOF LZTR1 variants identified in schwannomatosis patients and classified them according to current American College of Medical Genetics and Genomics/Association for Molecular Pathology/Association of Clinical Genomic Science guidelines. Subsequently, pathogenic/likely pathogenic schwannomatosis-associated LoF variants were compared with LoF LZTR1 variants reported in gnomAD data. Using current classification guidelines, 64/71 LoF LZTR1 variants reported in schwannomatosis patients in the literature were classified as pathogenic/likely pathogenic, and their frequency in probands 64/359 (17.8%) was significantly higher than the frequency of potential LoF variants identified in the general population (0.36%; p < 0.0001). The majority of published classifications of schwannomatosis-associated LoF variants are robust. However, the high frequency of LoF LZTR1 variants in the general population suggests that LZTR1 variants confer a reduced risk of schwannomas compared to germline NF2 and SMARCB1 pathogenic variants, making classification of novel variants challenging.

Targeted massively parallel sequencing of candidate regions on chromosome 22q predisposing to multiple schwannomas: An analysis of 51 individuals in a single-center experience.

Constitutional LZTR1 or SMARCB1 pathogenic variants (PVs) have been found in ∼86% of familial and ∼40% of sporadic schwannomatosis cases. Hence, we performed massively parallel sequencing of the entire LZTR1, SMARCB1, and NF2 genomic loci in 35 individuals with schwannomas negative for constitutional first-hit PVs in the LZTR1/SMARCB1/NF2 coding sequences; however, with 22q deletion and/or a different NF2 PV in each tumor, including six cases with only one tumor available. Furthermore, we verified whether any other LZTR1/SMARCB1/NF2 (likely) PVs could be found in 16 cases carrying a SMARCB1 constitutional variant in the 3'-untranslated region (3'-UTR) c.*17C>T, c.*70C>T, or c.*82C>T. As no additional variants were found, functional studies were performed to clarify the effect of these 3'-UTR variants on the transcript. The 3'-UTR variants c.*17C>T and c.*82C>T showed pathogenicity by negatively affecting the SMARCB1 transcript level. Two novel deep intronic SMARCB1 variants, c.500+883T>G and c.500+887G>A, resulting in out-of-frame missplicing of intron 4, were identified in two unrelated individuals. Further resequencing of the entire repeat-masked genomics sequences of chromosome 22q in individuals negative for PVs in the SMARCB1/LZTR1/NF2 coding- and noncoding regions revealed five potential schwannomatosis-predisposing candidate genes, that is, MYO18B, NEFH, SGSM1, SGSM3, and SBF1, pending further verification.

Dysregulated minor intron splicing in cancer.

Pre-mRNA splicing is now widely recognized as a cotranscriptional and post-transcriptional mechanism essential for regulating gene expression and modifying gene product function. Mutations in genes encoding core spliceosomal proteins and accessory regulatory splicing factors are now considered among the most recurrent genetic abnormalities in patients with cancer, particularly hematologic malignancies. These include mutations in the major (U2-type) and minor (U12-type) spliceosomes, which remove >99% and ~0.35% of introns, respectively. Growing evidence indicates that aberrant splicing of evolutionarily conserved U12-type minor introns plays a crucial role in cancer as the minor spliceosome component, ZRSR2, is subject to recurrent, leukemia-associated mutations, and intronic mutations have been shown to disrupt the splicing of minor introns. Here, we review the importance of minor intron regulation, the molecular effects of the minor (U12-type) spliceosomal mutations and cis-regulatory regions, and the development of minor intron studies for better understanding of cancer biology.

The molecular genetics of RASopathies: An update on novel disease genes and new disorders.

Enhanced signaling through RAS and the mitogen-associated protein kinase (MAPK) cascade underlies the RASopathies, a family of clinically related disorders affecting development and growth. In RASopathies, increased RAS-MAPK signaling can result from the upregulated activity of various RAS GTPases, enhanced function of proteins positively controlling RAS function or favoring the efficient transmission of RAS signaling to downstream transducers, functional upregulation of RAS effectors belonging to the MAPK cascade, or inefficient signaling switch-off operated by feedback mechanisms acting at different levels. The massive effort in RASopathy gene discovery performed in the last 20 years has identified more than 20 genes implicated in these disorders. It has also facilitated the characterization of several molecular activating mechanisms that had remained unappreciated due to their minor impact in oncogenesis. Here, we provide an overview on the discoveries collected during the last 5 years that have delivered unexpected insights (e.g., Noonan syndrome as a recessive disease) and allowed to profile new RASopathies, novel disease genes and new molecular circuits contributing to the control of RAS-MAPK signaling.

Updated diagnostic criteria and nomenclature for neurofibromatosis type 2 and schwannomatosis: An international consensus recommendation.

PURPOSE: Neurofibromatosis type 2 (NF2) and schwannomatosis (SWN) are genetically distinct tumor predisposition syndromes with overlapping phenotypes. We sought to update the diagnostic criteria for NF2 and SWN by incorporating recent advances in genetics, ophthalmology, neuropathology, and neuroimaging. METHODS: We used a multistep process, beginning with a Delphi method involving global disease experts and subsequently involving non-neurofibromatosis clinical experts, patients, and foundations/patient advocacy groups. RESULTS: We reached consensus on the minimal clinical and genetic criteria for diagnosing NF2 and SWN. These criteria incorporate mosaic forms of these conditions. In addition, we recommend updated nomenclature for these disorders to emphasize their phenotypic overlap and to minimize misdiagnosis with neurofibromatosis type 1. CONCLUSION: The updated criteria for NF2 and SWN incorporate clinical features and genetic testing, with a focus on using molecular data to differentiate the 2 conditions. It is likely that continued refinement of these new criteria will be necessary as investigators study the diagnostic properties of the revised criteria and identify new genes associated with SWN. In the revised nomenclature, the term "neurofibromatosis 2" has been retired to improve diagnostic specificity.

Concomitant variants in NF1, LZTR1 and GNAZ genes probably contribute to the aggressiveness of plexiform neurofibroma and warrant treatment with MEK inhibitor.

Neurofibromatosis 1 (NF1) is caused by germline mutations in the NF1 gene and manifests as proliferation of various tissues, including plexiform neurofibromas. The plexiform neurofibroma phenotype varies from indolent to locally aggressive, suggesting contributions of other modifiers in addition to somatic loss of NF1. In this study, we investigated a life-threatening plexiform neurofibroma in a 9-month-old female infant with NF1. Germline mutations in two RASopathy-associated genes were identified using whole-exome sequencing-a de novo pathogenic variant in the NF1 gene, and a known pathogenic variant in the LZTR1 gene. Somatic analysis of the plexiform neurofibroma revealed NF1 loss of heterozygosity and a variant in GNAZ, a gene encoding a G protein-coupled receptor. Cells expressing mutant GNAZ exhibited increased ERK 1/2 activation compared to those expressing wild-type GNAZ. Taken together, we suggest the variants in NF1, LZRT1 and GNAZ act synergistically in our patient, leading to MAPK pathway activation and contributing to the severity of the patient's plexiform neurofibromatosis. After treatment with the MEK inhibitor, trametinib, a prominent clinical improvement was observed in this patient. This case study contributes to the knowledge of germline and somatic non-NF1 variants affecting the NF1 clinical phenotype and supports use of personalized, targeted therapy.

Challenges in genetic diagnosis, co-occurrence of 22q11.2 deletion syndrome and Noonan syndrome.

Noonan syndrome (NS) is caused by pathogenic variants in genes involved in the RAS/MAPK pathway. On the other hand, 22q11.2 Deletion Syndrome (22q11.2DS) is caused by heterozygous microdeletion on chromosome 22q11.2. The clinical characteristics of both syndromes are expected to be relatively distinct, and, in fact, there is only one report of these syndromes occurring together, but on daily clinical practice and especially in early childhood phenotypes may overlap. In this study, we describe a patient with NS and 22q11.2DS features harboring a heterozygous 2.54 Mb deletion of chromosome 22q11.2 and a variant in LZTR1, c.1531G > A p.(Val511Met). In 1993, Wilson et al reported a patient with both 22q11.2DS and NS, proposing that probably more than one gene is deleted in the proband and that one of the deleted genes is responsible for Noonan's phenotype. In our patient, one of the deleted genes within the 22q11.2 region was the LZTR1 gene which was associated with NS in 2015. This case also highlights the importance of the long-term patients' follow-up to detect evolutionary changes that may appear in the phenotype and alerts clinicians of the co-occurrence of two syndromes that may manifest over time.

Clinical characteristics and genetic testing outcome of suspected hereditary peripheral nerve sheath tumours in a tertiary cancer institution in Singapore.

BACKGROUND: Peripheral Nerve Sheath Tumors (PNST) are a diverse group of mostly benign tumours uncommon in the general population. About 5-10% of PNSTs are hereditary, predominantly arising from germline variants in NF1, NF2, SMARCB1, or LZTR1 gene. METHODS: We reviewed the clinical characteristics and genetic testing results of patients referred to the NCIS Adult Cancer Genetics Clinic for suspected hereditary PNST. RESULTS: 3,001 patients suspected to have various hereditary cancer syndromes were evaluated between year 2000 to March 2021. 13 (0.4%) were clinically diagnosed to have hereditary PNSTs. The majority were male (54%), with a median age at presentation to the genetics clinic of 29 years (range 19-48). 11/13 (85%) patients had multiple PNSTs, 12/13 (92%) had young onset PNSTs, 5/13 (38.5%) had personal and family history of PNST. 11/13 patients (85%) had clinical features of neurofibromatosis type 1 (NF1) including one patient who also fulfilled clinical criteria of neurofibromatosis type 2 (NF2); 2/13 (14%) had multiple schwannomas. Four patients underwent multi-gene panel testing, including one patient with clinical NF1, one patient who met both clinical NF1 and NF2 criteria, and two patients with multiple schwannomas. The patient with clinical features of NF1 was heterozygous for a pathogenic c. 2033dup variant in the NF1 gene. The patient with both NF1/NF2 features was heterozygous for a novel c.732 T > A nonsense variant in the NF2 gene. The two patients with multiple schwannomas were heterozygous for a pathogenic/likely pathogenic variant in the LZTR1 gene and are the first LZTR1-positive schwannomatosis patients reported in Asia. CONCLUSION: Hereditary PNSTs are rare referrals to an adult cancer genetics clinic. NF1 is the most common PNST seen. LZTR1 variants may be the underlying cause in Asian patients with multiple schwannomatosis.

Epigenomic, genomic, and transcriptomic landscape of schwannomatosis.

Schwannomatosis (SWNTS) is a genetic cancer predisposition syndrome that manifests as multiple and often painful neuronal tumors called schwannomas (SWNs). While germline mutations in SMARCB1 or LZTR1, plus somatic mutations in NF2 and loss of heterozygosity in chromosome 22q have been identified in a subset of patients, little is known about the epigenomic and genomic alterations that drive SWNTS-related SWNs (SWNTS-SWNs) in a majority of the cases. We performed multiplatform genomic analysis and established the molecular signature of SWNTS-SWNs. We show that SWNTS-SWNs harbor distinct genomic features relative to the histologically identical non-syndromic sporadic SWNs (NS-SWNS). We demonstrate the existence of four distinct DNA methylation subgroups of SWNTS-SWNs that are associated with specific transcriptional programs and tumor location. We show several novel recurrent non-22q deletions and structural rearrangements. We detected the SH3PXD2A-HTRA1 gene fusion in SWNTS-SWNs, with predominance in LZTR1-mutant tumors. In addition, we identified specific genetic, epigenetic, and actionable transcriptional programs associated with painful SWNTS-SWNs including PIGF, VEGF, MEK, and MTOR pathways, which may be harnessed for management of this syndrome.

A Chinese family with Noonan syndrome caused by a heterozygous variant in LZTR1: a case report and literature review.

BACKGROUND: Noonan syndrome is an inherited disease involving multiple systems. More than 15 related genes have been discovered, among which LZTR1 was discovered recently. However, the pathogenesis and inheritance pattern of LZTR1 in Noonan syndrome have not yet been elucidated. CASE PRESENTATION: We herein describe a family with LZTR1-related Noonan syndrome. In our study, the proband, sister, mother, maternal aunt and grandmother and female cousin showed the typical or atypical features of Noonan syndrome. Only 3 patients underwent the whole-exome sequencing analysis and results showed that the proband as well as her sister inherited the same heterozygous LZTR1 variant (c.1149 + 1G > T) from their affected mother. Moreover, the proband accompanied by growth hormone deficiency without other associated variants. CONCLUSION: In a Chinese family with Noonan syndrome, we find that the c.1149 + 1G > T variant in LZTR1 gene shows a different autosomal dominant inheritance from previous reports, which changes our understanding of its inheritance and improves our understanding of Noonan syndrome.

Incidence of mosaicism in 1055 de novo NF2 cases: much higher than previous estimates with high utility of next-generation sequencing.

PURPOSE: To evaluate the incidence of mosaicism in de novo neurofibromatosis 2 (NF2). METHODS: Patients fulfilling NF2 criteria, but with no known affected family member from a previous generation (n = 1055), were tested for NF2 variants in lymphocyte DNA and where available tumor DNA. The proportion of individuals with a proven or presumed mosaic NF2 variant was assessed and allele frequencies of identified variants evaluated using next-generation sequencing. RESULTS: The rate of proven/presumed mosaicism was 232/1055 (22.0%). However, nonmosaic heterozygous pathogenic variants were only identified in 387/1055 (36.7%). When variant detection rates in second generation nonmosaics were applied to de novo cases, we assessed the overall probable mosaicism rate to be 59.7%. This rate differed by age from 21.7% in those presenting with bilateral vestibular schwannoma <20 years to 80.7% in those aged ≥60 years. A mosaic variant was detected in all parents of affected children with a single-nucleotide pathogenic NF2 variant. CONCLUSION: This study has identified a very high probable mosaicism rate in de novo NF2, probably making NF2 the condition with the highest expressed rate of mosaicism in de novo dominant disease that is nonlethal in heterozygote form. Risks to offspring are small and probably correlate with variant allele frequency detected in blood.

An update on the CNS manifestations of neurofibromatosis type 2.

Neurofibromatosis type II (NF2) is a tumor predisposition syndrome characterized by the development of distinctive nervous system lesions. NF2 results from loss-of-function alterations in the NF2 gene on chromosome 22, with resultant dysfunction of its protein product merlin. NF2 is most commonly associated with the development of bilateral vestibular schwannomas; however, patients also have a predisposition to development of other tumors including meningiomas, ependymomas, and peripheral, spinal, and cranial nerve schwannomas. Patients may also develop other characteristic manifestations such as ocular lesions, neuropathies, meningioangiomatosis, and glial hamartia. NF2 has a highly variable clinical course, with some patients exhibiting a severe phenotype and development of multiple tumors at an early age, while others may be nearly asymptomatic throughout their lifetime. Despite the high morbidity associated with NF2 in severe cases, management of NF2-associated lesions primarily consists of surgical resection and treatment of symptoms, and there are currently no FDA-approved systemic therapies that address the underlying biology of the syndrome. Refinements to the diagnostic criteria of NF2 have been proposed over time due to increasing understanding of clinical and molecular data. Large-population studies have demonstrated that some features such as the development of gliomas and neurofibromas, currently included as diagnostic criteria, may require further clarification and modification. Meanwhile, burgeoning insights into the molecular biology of NF2 have shed light on the etiology and highly variable severity of the disease and suggested numerous putative molecular targets for therapeutic intervention. Here, we review the clinicopathologic features of NF2, current understanding of the molecular biology of NF2, particularly with regard to central nervous system lesions, ongoing therapeutic studies, and avenues for further research.

Providing more evidence on LZTR1 variants in Noonan syndrome patients.

Noonan syndrome (NS, OMIM 163950) is a common autosomal dominant RASopathy caused mainly by gain-of-function germline pathogenic variants in genes involved in the RAS/MAPK signaling pathway. LZTR1 gene has been associated with both dominant and recessive NS. Here, we present seven patients with NS and variants in the LZTR1 gene from seven unrelated families, 14 individuals in total. The detection rAte of LZTR1 variants in our NS cohort was 4% similar to RAF1 and KRAS genes, indicating that variants in this gene might be frequent among our population. Three different variants were detected, c.742G>A (p.Gly248Arg), c.360C>A (p.His120Gln), and c.2245T>C (p.Tyr749His). The pathogenic variant c.742G>A (p.Gly248Arg) was found in five/seven patients. In our cohort 50% of patients presented heart defects and neurodevelopment delay or learning disabilities, short stature was present in 21% of them and one patient had acute lymphoblastic leukemia. This study broadens the spectrum of variants in the LZTR1 gene and provides increased knowledge of the clinical phenotypes observed in Argentinean NS patients.

Cullin 3 and Its Role in Tumorigenesis.

Cullin 3 (Cul3) family of ubiquitin ligases comprises three components, the RING finger protein RBX1, the Cul3 scaffold, and a Bric-a-brac/Tramtrack/Broad complex (BTB) protein. The BTB protein serves as a bridge to connect Cul3 to substrate and is functionally equivalent to the combination of substrate adaptor and linker in other Cullin complexes. Human genome encodes for ~180 BTB proteins, implying a broad spectrum of ubiquitination signals and substrate repertoire. Accordingly, Cul3 ubiquitin ligases are involved in diverse cellular processes, including cell division, differentiation, cytoskeleton remodeling, stress responses, and nerve cell functions. Emerging evidence has pointed to the prominent role of Cul3 ubiquitin ligases in cancer. This chapter will describe recent advances on the roles of Cul3 E3 ligase complexes in regulating various cancer hallmarks and therapeutic responses and the mutation/dysregulation of Cul3 substrate adaptors in cancer. In particular, we will focus on several extensively studied substrate adaptors, such as Keap1, SPOP, KLHL20, and LZTR1, and will also discuss other recently identified Cul3 adaptors with oncogenic or tumor-suppressive functions. We conclude that Cul3 ubiquitin ligases represent master regulators of human malignancies and highlight the importance of developing modulating agents for oncogenic/tumor-suppressive Cul3 E3 ligase complexes to prevent or intervene tumorigenesis.

Identifying the deficiencies of current diagnostic criteria for neurofibromatosis 2 using databases of 2777 individuals with molecular testing.

PURPOSE: We have evaluated deficiencies in existing diagnostic criteria for neurofibromatosis 2 (NF2). METHODS: Two large databases of individuals fulfilling NF2 criteria (n = 1361) and those tested for NF2 variants with criteria short of diagnosis (n = 1416) were interrogated. We assessed the proportions meeting each diagnostic criterion with constitutional or mosaic NF2 variants and the positive predictive value (PPV) with regard to definite diagnosis. RESULTS: There was no evidence for usefulness of old criteria "glioma" or "neurofibroma." "Ependymoma" had 100% PPV and high levels of confirmed NF2 diagnosis (67.7%). Those with bilateral vestibular schwannoma (VS) alone aged ≥60 years had the lowest confirmation rate (6.6%) and reduced PPV (80%). Siblings as a first-degree relative, without an affected parent, had 0% PPV. All three individuals with unilateral VS and an affected sibling were proven not to have NF2. The biggest overlap was with LZTR1-associated schwannomatosis. In this category, seven individuals with unilateral VS plus ≥2 nondermal schwannomas reduced PPV to 67%. CONCLUSIONS: The present study confirms important deficiencies in NF2 diagnostic criteria. The term "glioma" should be dropped and replaced by "ependymoma." Similarly "neurofibroma" should be removed. Dropping "sibling" from first-degree relatives should be considered and testing of LZTR1 should be recommended for unilateral VS.

Delineation of dominant and recessive forms of LZTR1-associated Noonan syndrome.

Noonan syndrome (NS) is characterised by distinctive facial features, heart defects, variable degrees of intellectual disability and other phenotypic manifestations. Although the mode of inheritance is typically dominant, recent studies indicate LZTR1 may be associated with both dominant and recessive forms. Seeking to describe the phenotypic characteristics of LZTR1-associated NS, we searched for likely pathogenic variants using two approaches. First, scrutiny of exomes from 9624 patients recruited by the Deciphering Developmental Disorders (DDDs) study uncovered six dominantly-acting mutations (p.R97L; p.Y136C; p.Y136H, p.N145I, p.S244C; p.G248R) of which five arose de novo, and three patients with compound-heterozygous variants (p.R210*/p.V579M; p.R210*/p.D531N; c.1149+1G>T/p.R688C). One patient also had biallelic loss-of-function mutations in NEB, consistent with a composite phenotype. After removing this complex case, analysis of human phenotype ontology terms indicated significant phenotypic similarities (P = 0.0005), supporting a causal role for LZTR1. Second, targeted sequencing of eight unsolved NS-like cases identified biallelic LZTR1 variants in three further subjects (p.W469*/p.Y749C, p.W437*/c.-38T>A and p.A461D/p.I462T). Our study strengthens the association of LZTR1 with NS, with de novo mutations clustering around the KT1-4 domains. Although LZTR1 variants explain ~0.1% of cases across the DDD cohort, the gene is a relatively common cause of unsolved NS cases where recessive inheritance is suspected.

Schwannomatosis: a genetic and epidemiological study.

OBJECTIVES: Schwannomatosis is a dominantly inherited condition predisposing to schwannomas of mainly spinal and peripheral nerves with some diagnostic overlap with neurofibromatosis-2 (NF2), but the underlying epidemiology is poorly understood. We present the birth incidence and prevalence allowing for overlap with NF2. METHODS: Schwannomatosis and NF2 cases were ascertained from the Manchester region of England (population=4.8 million) and from across the UK. Point prevalence and birth incidence were calculated from regional birth statistics. Genetic analysis was also performed on NF2, LZTR1 and SMARCB1 on blood and tumour DNA samples when available. RESULTS: Regional prevalence for schwannomatosis and NF2 were 1 in 126 315 and 50 500, respectively, with calculated birth incidences of 1 in 68 956 and 1 in 27 956. Mosaic NF2 causes a substantial overlap with schwannomatosis resulting in the misdiagnosis of at least 9% of schwannomatosis cases. LZTR1-associated schwannomatosis also causes a small number of cases that are misdiagnosed with NF2 (1%-2%), due to the occurrence of a unilateral vestibular schwannoma. Patients with schwannomatosis had lower numbers of non-vestibular cranial schwannomas, but more peripheral and spinal nerve schwannomas with pain as a predominant presenting symptom. Life expectancy was significantly better in schwannomatosis (mean age at death 76.9) compared with NF2 (mean age at death 66.2; p=0.004). CONCLUSIONS: Within the highly ascertained North-West England population, schwannomatosis has less than half the birth incidence and prevalence of NF2.

Constitutional LZTR1 mutation presenting with a unilateral vestibular schwannoma in a teenager.

Schwannomatosis is a rare neurofibromatosis clinically diagnosed by age-dependent criteria, with bilateral vestibular schwannoma and/or a constitutional NF2 mutation representing exclusion criteria. Following SMARCB1 germline mutations, constitutional mutations in LZTR1 were discovered. We report on the molecular investigation in a patient presenting at 14 years with a unilateral vestibular schwannoma, ultimately causing blindness and unilateral hearing loss, in the absence of other schwannomas or a positive family history. In DNA derived from frozen tumor tissue, a comprehensive NF2, SMARCB1 and LZTR1 analysis showed an NF2 truncating mutation c.1006_1021delins16; an LZTR1 mutation c.791+1G>A; and a partial 22q deletion including NF2, SMARCB1 and LZTR1. Sequence analysis on peripheral blood derived DNA showed the LZTR1 mutation to be constitutional, but the NF2 mutation and partial 22q deletion were not found, indicating them to be somatic events. RNA-based targeted analysis confirmed missplicing of LZTR1 intron 8, predicted to result in a premature stop codon. This LZTR1 mutation was paternally inherited. While isolated vestibular schwannoma or NF2 may be considered in a young individual with a unilateral vestibular schwannoma, this report suggests that LZTR1 -related schwannomatosis be added to this differential diagnosis.