Francesca Boaretto

Germline mutations in TMEM127 confer susceptibility to pheochromocytoma

Pheochromocytomas, which are catecholamine-secreting tumors of neural crest origin, are frequently hereditary. However, the molecular basis of the majority of these tumors is unknown. We identified the transmembrane-encoding gene TMEM127 on chromosome 2q11 as a new pheochromocytoma susceptibility gene. In a cohort of 103 samples, we detected truncating germline TMEM127 mutations in approximately 30% of familial tumors and about 3% of sporadic-appearing pheochromocytomas without a known genetic cause. The wild-type allele was consistently deleted in tumor DNA, suggesting a classic mechanism of tumor suppressor gene inactivation. Pheochromocytomas with mutations in TMEM127 are transcriptionally related to tumors bearing NF1 mutations and, similarly, show hyperphosphorylation of mammalian target of rapamycin (mTOR) effector proteins. Accordingly, in vitro gain-of-function and loss-of-function analyses indicate that TMEM127 is a negative regulator of mTOR. TMEM127 dynamically associates with the endomembrane system and colocalizes with perinuclear (activated) mTOR, suggesting a subcompartmental-specific effect. Our studies identify TMEM127 as a tumor suppressor gene and validate the power of hereditary tumors to elucidate cancer pathogenesis.

Spectrum and prevalence of FP/TMEM127 gene mutations in pheochromocytomas and paragangliomas.

CONTEXT Pheochromocytomas and paragangliomas are genetically heterogeneous neural crest-derived neoplasms. We recently identified germline mutations of the novel transmembrane-encoding gene FP/TMEM127 in familial and sporadic pheochromocytomas consistent with a tumor suppressor effect. OBJECTIVES To examine the prevalence and spectrum of FP/TMEM127 mutations in pheochromocytomas and paragangliomas and to test the effect of mutations in vitro. DESIGN, SETTING, AND PARTICIPANTS We sequenced the FP/TMEM127 gene in 990 individuals with pheochromocytomas and/or paragangliomas, including 898 previously unreported cases without mutations in other susceptibility genes from 8 independent worldwide referral centers between January 2009 and June 2010. A multiplex polymerase chain reaction-based method was developed to screen for large gene deletions in 545 of these samples. Confocal microscopy of 5 transfected mutant proteins was used to determine their subcellular localization. MAIN OUTCOME MEASURES The frequency and type of FP/TMEM127 mutation or deletion was assessed and correlated with clinical variables; the subcellular localization of 5 overexpressed mutants was compared with wild-type FP/TMEM127 protein. RESULTS We identified 19 potentially pathogenic FP/TMEM127 germline mutations in 20 independent families, but no large deletions were detected. All mutation carriers had adrenal tumors, including 7 bilateral (P = 2.7 × 10(-4)) and/or with familial disease (5 of 20 samples; P = .005). The median age at disease onset in the FP/TMEM127 mutation group was similar to that of patients without a mutation (41.5 vs 45 years, respectively; P = .54). The most common presentation was that of a single benign adrenal tumor in patients older than 40 years. Malignancy was seen in 1 mutation carrier (5%). Expression of 5 novel FP/TMEM127 mutations in cell lines revealed diffuse localization of the mutant proteins in contrast with the discrete multiorganelle distribution of wild-type TMEM127. CONCLUSIONS Germline mutations of FP/TMEM127 were associated with pheochromocytoma but not paraganglioma and occurred in an age group frequently excluded from genetic screening algorithms. Disease-associated mutations disrupt intracellular distribution of the FP/TMEM127 protein.

A Novel Mutation in the Upstream Open Reading Frame of the CDKN1B Gene Causes a MEN4 Phenotype

The CDKN1B gene encodes the cyclin-dependent kinase inhibitor p27KIP1, an atypical tumor suppressor playing a key role in cell cycle regulation, cell proliferation, and differentiation. Impaired p27KIP1 expression and/or localization are often observed in tumor cells, further confirming its central role in regulating the cell cycle. Recently, germline mutations in CDKN1B have been associated with the inherited multiple endocrine neoplasia syndrome type 4, an autosomal dominant syndrome characterized by varying combinations of tumors affecting at least two endocrine organs. In this study we identified a 4-bp deletion in a highly conserved regulatory upstream ORF (uORF) in the 5′UTR of the CDKN1B gene in a patient with a pituitary adenoma and a well-differentiated pancreatic neoplasm. This deletion causes the shift of the uORF termination codon with the consequent lengthening of the uORF–encoded peptide and the drastic shortening of the intercistronic space. Our data on the immunohistochemical analysis of the patients pancreatic lesion, functional studies based on dual-luciferase assays, site-directed mutagenesis, and on polysome profiling show a negative influence of this deletion on the translation reinitiation at the CDKN1B starting site, with a consequent reduction in p27KIP1 expression. Our findings demonstrate that, in addition to the previously described mechanisms leading to reduced p27KIP1 activity, such as degradation via the ubiquitin/proteasome pathway or non-covalent sequestration, p27KIP1 activity can also be modulated by an uORF and mutations affecting uORF could change p27KIP1 expression. This study adds the CDKN1B gene to the short list of genes for which mutations that either create, delete, or severely modify their regulatory uORFs have been associated with human diseases.

Genome-wide scan supports the existence of a susceptibility locus for schizophrenia and bipolar disorder on chromosome 15q26.

Schizophrenia (SZ) and bipolar disorder (BPD) are two severe psychiatric diseases with a strong genetic component. In agreement with the ‘continuum theory’, which suggests an overlap between these disorders, the existence of genes that affect simultaneously susceptibility to SZ and BPD has been hypothesized. In this study we performed a 7.5 cM genome scan in a sample of 16 families affected by SZ and BPD, all originating from the same northeast Italian population. Using both parametric and non-parametric analyses we identified linkage peaks on four regions (1p, 1q, 4p and 15q), which were then subjected to a follow-up study with an increased marker density. The strongest linkage was obtained on chromosome 15q26 with a non-parametric linkage of 3.05 for marker D15S1014 (nominal P=0.00197). Interestingly, evidence for linkage with the same marker has been reported previously by an independent study performed on SZ and BPD families from Quebec. In this region, the putative susceptibility gene ST8SIA2 (also known as SIAT8B) was recently associated with SZ in a Japanese sample. However, our allele frequency analyses of the two single-nucleotide polymorphisms (SNPs) with putative functional outcome (rs3759916 and rs3759914) suggest that these polymorphisms are unlikely to be directly involved in SZ in our population. In conclusion, our results support the presence of a gene in 15q26 that influences the susceptibility to both SZ and BPD.

Infancy onset hereditary spastic paraplegia associated with a novel atlastin mutation

Cerebral palsy is the most common cause of spastic paraplegia affecting infants. However, spasticity characterized by progressive gait impairment may also be the first sign of infantile onset hereditary spastic paraplegia (HSP).1 We studied a family with six affected members (figure). Figure. Pedigree of the family with SPG3A . Arrow indicates the index case; blackened and unblackened symbols represent affected and unaffected individuals. Physic map is according to information from the UCSC Genome Browser. Boxes represent the disease-bearing chromosome. The first patient (II-3) had slowly progressive leg spasticity and weakness that started in infancy. She and her second son (III-2) had mild cyanosis at birth, and for that reason their first diagnosis was cerebral palsy. The clinical history is similar for all affected members: normal pregnancy and delivery, motor impairment starting before gait acquisition, and normal cognitive and language development. Clinical characteristics are summarized in table E-1 (see www.neurology.org). All affected members presented delayed motor milestones and gait impairment. There was no sphincteric disturbance. Current neurologic examination revealed severe spastic paraparesis, …

SEVERE CMT TYPE 2 WITH FATAL ENCEPHALOPATHY ASSOCIATED WITH A NOVEL MFN2 SPLICING MUTATION

Mutations in the MFN2 gene, encoding mitofusin2, cause autosomal dominant axonal Charcot-Marie-Tooth type 2 (CMT2A, MIM: 608507).1 MFN2 mutations are also found in CMT2 subjects with optic atrophy2 or cognitive impairment.3 The sibship we studied comprised 3 affected and 3 apparently healthy individuals (figure e-1 on the Neurology ® Web site at www.neurology.org). ### Standard protocol approvals, registrations, and patient consents. The study was approved by the institutional ethics committee. Written informed consent was obtained from all participants in the study. ### Clinical cases and results. For more information, see e-Methods. A 48-year-old woman presented with a 10-year history of progressive leg weakness, foot drop, hypotrophy, areflexia, intact sensation, and cognition. Neurophysiology (table e-1) revealed a severe axonal polyneuropathy. The sural nerve biopsy (figure e-2, A and B) showed reduced fiber densities, loss of large myelinated fibers, and marginal Wallerian degeneration. Teased fibers were thin, with shortened internodes, some ongoing remyelination, and no demyelination. She was wheelchair-bound within 1 year. At age 50, after colectomy, she developed a progressive brainstem syndrome with vomiting, nystagmus, chorea, clouded consciousness, and dysautonomia (hyperthermia, breathing irregularities). MRI showed diffuse T2 hyperintensities in the upper brainstem and periaqueductal gray (figure 1A). Blood and CSF examinations were unremarkable. The patient progressively worsened in spite of aggressive management, including thiamine supplementation, and died 7 days later. Brain pathology revealed symmetric vasculonecrotic lesions in the brainstem and the periaqueductal gray with small hemorrhagic component (figure e-2, C and D). Figure 1 Neuroimaging and molecular data of index case (A) Fluid-attenuated inversion recovery axial (a) and coronal (b) images of case II-7 2 days after onset of the encephalopathic symptoms. Symmetric high signal intensity alterations surround the aqueduct, involve the medial thalami, the mammillary bodies, and the tegmental area. (B) Sequence of the wild-type (WT) and mutated (Mut) MFN2 …

Point mutations and a large intragenic deletion in SPG11 in complicated spastic paraplegia without thin corpus callosum

Background: Hereditary spastic paraplegia (HSP) with thin corpus callosum (HSP-TCC) is a frequent subtype of complicated HSP clinically characterised by slowly progressive spastic paraparesis with cognitive impairment and thin corpus callosum (TCC). SPG11, the gene associated with the major locus involved, encodes spatacsin, a protein of unknown function. Methods: Different types of mutations were identified in patients with the complex form of HSP (cHSP) including TCC. We screened a series of 45 index patients with different types of cHSP with (n = 10) and without (n = 35) TCC. Results: Ten mutations, of which five are novel, were detected in seven patients. Of importance, three out of seven mutated patients present with cHSP without TCC. Among the novel mutations identified, we characterised a large intragenic rearrangement deleting 2.6 kb of the SPG11 gene. The rearrangement is due to non-allelic homologous recombination between Alu sequences flanking the breakpoints. Conclusions: These findings expand the mutation spectrum of SPG11 and suggest that SPG11 mutations may occur more frequently in familial than sporadic forms of cHSP without TCC. This helps to define further clinical and molecular criteria for a correct diagnosis of the SPG11 related form of cHSP. In addition, the intragenic deletion detected here, and the mechanism involved, both provide clues to address the issue of SPG11 missing mutant alleles previously reported.

Loss-of-function mutations in the SIGMAR1 gene cause distal hereditary motor neuropathy by impairing ER-mitochondria tethering and Ca2+ signalling

Distal hereditary motor neuropathies (dHMNs) are clinically and genetically heterogeneous neurological conditions characterized by degeneration of the lower motor neurons. So far, 18 dHMN genes have been identified, however, about 80% of dHMN cases remain without a molecular diagnosis. By a combination of autozygosity mapping, identity-by-descent segment detection and whole-exome sequencing approaches, we identified two novel homozygous mutations in the SIGMAR1 gene (p.E138Q and p.E150K) in two distinct Italian families affected by an autosomal recessive form of HMN. Functional analyses in several neuronal cell lines strongly support the pathogenicity of the mutations and provide insights into the underlying pathomechanisms involving the regulation of ER-mitochondria tethering, Ca2+ homeostasis and autophagy. Indeed, in vitro, both mutations reduce cell viability, the formation of abnormal protein aggregates preventing the correct targeting of sigma-1R protein to the mitochondria-associated ER membrane (MAM) and thus impinging on the global Ca2+ signalling. Our data definitively demonstrate the involvement of SIGMAR1 in motor neuron maintenance and survival by correlating, for the first time in the Caucasian population, mutations in this gene to distal motor dysfunction and highlight the chaperone activity of sigma-1R at the MAM as a critical aspect in dHMN pathology.

Multiple endocrine neoplasia syndrome type 1: institution, management, and data analysis of a nationwide multicenter patient database

ObjectiveThe aim of this study was to integrate European epidemiological data on patients with multiple endocrine neoplasia type 1 by creating an Italian registry of this syndrome, including clinical and genetic characteristics and therapeutic management.MethodsClinical, familial and genetic data of patients with multiple endocrine neoplasia type 1, diagnosed, treated, and followed-up for a mean time of 11.3 years, in 14 Italian referral endocrinological centers, were collected, over a 3-year course (2011–2013), to build a national electronic database.ResultsThe Italian multiple endocrine neoplasia type 1 database includes 475 patients (271 women and 204 men), of whom 383 patients (80.6%) were classified as familial cases (from 136 different pedigrees), and 92 (19.4%) patients were sporadic cases. A MEN1 mutation was identified in 92.6% of familial cases and in 48.9% of sporadic cases. Four hundred thirty-six patients were symptomatic, presenting primary hyperparathyroidism, gastroenteropancreatic neuroendocrine tumors and pituitary tumors in 93, 53, and 41% of cases, respectively. Thirty-nine subjects, belonging to affected pedigrees positive for a MEN1 mutation, were asymptomatic at clinical and biochemical screening. Age at diagnosis of multiple endocrine neoplasia type 1 probands was similar for both familial and simplex cases (mean age 47.2 ± 15.3 years). In familial cases, diagnosis of multiple endocrine neoplasia type 1 in relatives of affected probands was made more than 10 years in advance (mean age at diagnosis 36.5 ± 17.6 years).ConclusionsThe analysis of Italian registry of multiple endocrine neoplasia type 1 patients revealed that clinical features of Italian multiple endocrine neoplasia type 1 patients are similar to those of other western countries, and confirmed that the genetic test allowed multiple endocrine neoplasia type 1 diagnosis 10 years earlier than biochemical or clinical diagnosis.

A novel SACS mutation results in non-ataxic spastic paraplegia and peripheral neuropathy.

Mutations in the SACS gene are commonly associated with autosomal recessive spastic ataxia of Charlevoix‐Saguenay (ARSACS), a complex neurodegenerative disorder characterized by progressive degeneration of the cerebellum and spinal cord tracts. The aim of this study was to identify the genetic cause of the disease in an Italian family with spastic paraplegia and peripheral neuropathy.