Jean-Paul Bonnefont

Somatic deletion of the imprinted 11p15 region in sporadic persistent hyperinsulinemic hypoglycemia of infancy is specific of focal adenomatous hyperplasia and endorses partial pancreatectomy.

Sporadic persistent hyperinsulinemic hypoglycemia of infancy (PHHI) or nesidioblastosis is a heterogeneous disorder characterized by profound hypoglycemia due to inappropriate hypersecretion of insulin. An important diagnostic goal is to distinguish patients with a focal hyperplasia of islet cells of the pancreas (FoPHHI) from those with a diffuse abnormality of islets (DiPHHI) because management strategies differ significantly. 16 infants with sporadic PHHI resistant to diazoxide and who underwent pancreatectomy were investigated. Selective pancreatic venous sampling coupled with peroperative surgical examination and analysis of extemporaneous frozen sections allowed us to identify 10 cases with FoPHHI and 6 cases with DiPHHI. We show here that in cases of FoPHHI, but not those of DiPHHI, there was specific loss of maternal alleles of the imprinted chromosome region 11p15 in cells of the hyperplastic area of the pancreas but not in normal pancreatic cells. This somatic event is consistent with a proliferative monoclonal lesion. It involves disruption of the balance between monoallelic expression of several maternally and paternally expressed genes. Thus, we provide the first molecular explanation of the heterogeneity of sporadic forms of PHHI such that it is possible to perform only partial pancreatectomy, limited to the focal somatic lesion, so as to avoid iatrogenic diabetes in patients with focal adenomatous hyperplasia.

Genetic characterization of congenital tufting enteropathy: epcam associated phenotype and involvement of SPINT2 in the syndromic form.

Congenital tufting enteropathy (CTE) is a rare and severe enteropathy recently ascribed to mutations in the epcam gene. Here we establish SPINT2, previously ascribed to congenital sodium diarrhea, as a second gene associated with CTE and report molecular and immunohistochemistry data in 57 CTE patients. Inclusion criteria were early onset diarrhea and intestinal insufficiency with the typical histological CTE abnormalities. The clinical phenotype was registered, the entire coding regions of epcam and SPINT2 sequenced, and immunostaining of EpCAM and SPINT2 performed on intestinal biopsies. An epcam mutation was involved in 41 patients (73xa0%) who mainly displayed isolated digestive symptoms. Mutations severely affected gene expression since the EpCAM signal on intestinal tissues was either undetectable or low and irregular. Twelve other patients (21xa0%) carried mutations in SPINT2, and were phenotypically characterized by systematic association with keratitis (pxa0<xa010−4) and, for half of them, with choanal atresia (pxa0<xa010−4). Dependency on parenteral nutrition (PN) was comparable in patients with epcam or SPINT2 mutations, but the frequent epcam mutation c.556-14A>G (abnormal splicing) was significantly associated with a better outcome (pxa0=xa00.032) with milder PN dependency to weaning in some cases. Finally, four patients (7xa0%) with isolated digestive symptoms had no detectable epcam or SPINT2 mutation. Two candidate genes, Elf3 and Claudin7, were excluded from this population. Our study allows us to separate CTE patients into at least three genetic classes, each with specific phenotypes. The genetics approach raises the question of the distinction between two congenital enteropathies. Our findings should help improve the diagnosis of CTE, guide toward strategies of long-term PN management, and limit indications for intestinal transplantation to life-threatening PN complications.

Relative frequencies of inherited retinal dystrophies and optic neuropathies in Southern France: assessment of 21-year data management.

ABSTRACT Purpose: Inherited retinal dystrophies (IRDs) and inherited optic neuropathies (IONs) are rare diseases defined by specific clinical and molecular features. The relative prevalence of these conditions was determined in Southern France. Methods: Patients recruited from a specialized outpatient clinic over a 21-year period underwent extensive clinical investigations and 107 genes were screened by polymerase chain reaction/sequencing. Results: There were 1957 IRD cases (1481 families) distributed in 70% of pigmentary retinopathy cases (56% non-syndromic, 14% syndromic), 20% maculopathies and 7% stationary conditions. Patients with retinitis pigmentosa were the most frequent (47%) followed by Usher syndrome (10.8%). Among non-syndromic pigmentary retinopathy patients, 84% had rod-cone dystrophy, 8% cone-rod dystrophy and 5% Leber congenital amaurosis. Macular dystrophies were encountered in 398 cases (30% had Stargardt disease and 11% had Best disease). There were 184 ION cases (127 families) distributed in 51% with dominant optic neuropathies, 33% with recessive/sporadic forms and 16% with Leber hereditary optic neuropathy. Positive molecular results were obtained in 417/609 families with IRDs (68.5%) and in 27/58 with IONs (46.5%). The sequencing of 5 genes (ABCA4, USH2A, MYO7A, RPGR and PRPH2) provided a positive molecular result in 48% of 417 families with IRDs. Except for autosomal retinitis pigmentosa, in which less than half the families had positive molecular results, about 75% of families with other forms of retinal conditions had a positive molecular diagnosis. Conclusions: Although gene discovery considerably improved molecular diagnosis in many subgroups of IRDs and IONs, retinitis pigmentosa, accounting for almost half of IRDs, remains only partly molecularly defined.

The first founder DGUOK mutation associated with hepatocerebral mitochondrial DNA depletion syndrome

Deoxyguanosine kinase (dGK) deficiency is a frequent cause of mitochondrial DNA depletion associated with a hepatocerebral phenotype. In this study, we describe a new splice site mutation in the DGUOK gene and the clinical, radiologic, and genetic features of these DGUOK patients. This new DGUOK homozygous mutation (c.444-62C>A) was identified in three patients from two North-African consanguineous families with combined respiratory chain deficiencies and mitochondrial DNA depletion in the liver. Brain MRIs are normal in DGUOK patients in the literature. Interestingly, we found subtentorial abnormal myelination and moderate hyperintensity in the bilateral pallidi in our patients. This new mutation creates a cryptic splice site in intron 3 (in position -62) and is predicted to result in a larger protein with an in-frame insertion of 20 amino acids. In silico analysis of the putative impact of the insertion shows serious clashes in protein conformation: this insertion disrupts the alpha5 helix of the dGK kinase domain, rendering the protein unable to bind purine deoxyribonucleosides. In addition, a common haplotype that segregated with the disease in both families was detected by haplotype reconstruction with 10 markers (microsatellites and SNPs), which span 4.6 Mb of DNA covering the DGUOK locus. In conclusion, we report a new DGUOK splice site mutation that provide insight into a critical protein domain (dGK kinase domain) and the first founder mutation in a North-African population.

Update on Lysinuric Protein Intolerance, a Multi-faceted Disease Retrospective cohort analysis from birth to adulthood

BackgroundLysinuric protein intolerance (LPI) is a rare metabolic disease resulting from recessive-inherited mutations in the SLC7A7 gene encoding the cationic amino-acids transporter subunit y+LAT1. The disease is characterised by protein-rich food intolerance with secondary urea cycle disorder, but symptoms are heterogeneous ranging from infiltrative lung disease, kidney failure to auto-immune complications. This retrospective study of all cases treated at Necker Hospital (Paris, France) since 1977 describes LPI in both children and adults in order to improve therapeutic management.ResultsSixteen patients diagnosed with LPI (12 males, 4 females, from 9 families) were followed for a mean of 11.4 years (min-max: 0.4-37.0 years). Presenting signs were failure to thrive (nu2009=u20099), gastrointestinal disorders (nu2009=u20092), cytopenia (nu2009=u20096), hyperammonemia (nu2009=u200910) with acute encephalopathy (nu2009=u20094) or developmental disability (nu2009=u20093), and proteinuria (nu2009=u20091). During follow-up, 5 patients presented with acute hyperammonemia, and 8 presented with developmental disability. Kidney disease was observed in all patients: tubulopathy (11/11), proteinuria (4/16) and kidney failure (7/16), which was more common in older patients (mean age of onset 17.7 years, standard deviation 5.33 years), with heterogeneous patterns including a lupus nephritis. We noticed a case of myocardial infarction in a 34-year-old adult. Failure to thrive and signs of haemophagocytic-lymphohistiocytosis were almost constant. Recurrent acute pancreatitis occurred in 2 patients. Ten patients developed an early lung disease. Six died at the mean age of 4 years from pulmonary alveolar proteinosis. This pulmonary involvement was significantly associated with death. Age-adjusted plasma lysine concentrations at diagnosis showed a trend toward increased values in patients with a severe disease course and premature death (Wilcoxon pu2009=u20090.08; logrank, pu2009=u20090.17). Age at diagnosis was a borderline predictor of overall survival (logrank, pu2009=u20090.16).ConclusionsAs expected, early pulmonary involvement with alveolar proteinosis is frequent and severe, being associated with an increased risk of death. Kidney disease frequently occurs in older patients. Cardiovascular and pancreatic involvement has expanded the scope of complications. A borderline association between increased levels of plasma lysine and poorer outome is suggested. Greater efforts at prevention are warranted to optimise the long-term management in these patients.

Lack of interaction between NEMO and SHARPIN impairs linear ubiquitination and NF-κB activation and leads to incontinentia pigmenti

Background: Incontinentia pigmenti (IP; MIM308300) is a severe, male‐lethal, X‐linked, dominant genodermatosis resulting from loss‐of‐function mutations in the IKBKG gene encoding nuclear factor &kgr;B (NF‐&kgr;B) essential modulator (NEMO; the regulatory subunit of the I&kgr;B kinase [IKK] complex). In 80% of cases of IP, the deletion of exons 4 to 10 leads to the absence of NEMO and total inhibition of NF‐&kgr;B signaling. Here we describe a new IKBKG mutation responsible for IP resulting in an inactive truncated form of NEMO. Objectives: We sought to identify the mechanism or mechanisms by which the truncated NEMO protein inhibits the NF‐&kgr;B signaling pathway. Methods: We sequenced the IKBKG gene in patients with IP and performed complementation and transactivation assays in NEMO‐deficient cells. We also used immunoprecipitation assays, immunoblotting, and an in situ proximity ligation assay to characterize the truncated NEMO protein interactions with IKK‐&agr;, IKK‐&bgr;, TNF receptor–associated factor 6, TNF receptor–associated factor 2, receptor‐interacting protein 1, Hemo‐oxidized iron regulatory protein 2 ligase 1 (HOIL‐1), HOIL‐1–interacting protein, and SHANK‐associated RH domain–interacting protein. Lastly, we assessed NEMO linear ubiquitination using immunoblotting and investigated the formation of NEMO‐containing structures (using immunostaining and confocal microscopy) after cell stimulation with IL‐1&bgr;. Results: We identified a novel splice mutation in IKBKG (c.518+2T>G, resulting in an in‐frame deletion: p.DelQ134_R256). The mutant NEMO lacked part of the CC1 coiled‐coil and HLX2 helical domain. The p.DelQ134_R256 mutation caused inhibition of NF‐&kgr;B signaling, although the truncated NEMO protein interacted with proteins involved in activation of NF‐&kgr;B signaling. The IL‐1&bgr;–induced formation of NEMO‐containing structures was impaired in fibroblasts from patients with IP carrying the truncated NEMO form (as also observed in HOIL‐1−/− cells). The truncated NEMO interaction with SHANK‐associated RH domain–interacting protein was impaired in a male fetus with IP, leading to defective linear ubiquitination. Conclusion: We identified a hitherto unreported disease mechanism (defective linear ubiquitination) in patients with IP.

Intellectual disability associated with retinal dystrophy in the Xp11.3 deletion syndrome: ZNF674 on trial. Guilty or innocent?

X-linked retinal dystrophies (XLRD) are listed among the most severe RD owing to their early onset, leading to significant visual loss before the age of 30. One-third of XLRD are accounted for by RP2 mutations at the Xp11.23 locus. Deletions of ca. 1.2u2009Mb in the Xp11.3-p11.23 region have been previously reported in two independent families segregating XLRD with intellectual disability (ID). Although the RD was ascribed to the deletion of RP2, the ID was suggested to be accounted for by the loss of ZNF674, which mutations were independently reported to account for isolated XLID. Here, we report deletions in the Xp11.3-p11.23 region responsible for the loss of ZNF674 in two unrelated families segregating XLRD, but no ID, identified by chromosomal microarray analysis. These findings question the responsibility of ZNF674 deletions in ID associated with X-linked retinal dystrophy.

Could Failure in Preimplantation Genetic Diagnosis Justify Editing the Human Embryo Genome

Julie Steffann,1,* Pierre Jouannet,2 Jean-Paul Bonnefont,1 Hervé Chneiweiss,3 and Nelly Frydman4 1Université Paris Descartes – Sorbonne Paris Cité, Imagine INSERM UMR1163, Service de Génétique, Groupe hospitalier Necker-Enfants Malades, AP-HP, 75006, Paris, France 2Université Paris Descartes, French National Academy of Medicine & Comité d’éthique de l’Inserm, 75006 Paris, France 3Sorbonne Université, Neuroscience Paris Seine UMR8246 CNRS/U1130 Inserm/UMCR18 Université Pierre et Marie Curie, Paris, France & Comité d’éthique de l’Inserm, 75005 Paris, France 4AP-HP, Biologie de la reproduction, Université Paris-Sud, Université Paris-Saclay, Hôpital Antoine-Béclère, Clamart, F-92140 France *Correspondence: julie.steffann@aphp.fr https://doi.org/10.1016/j.stem.2018.01.004

High predictive value of brain MRI imaging in primary mitochondrial respiratory chain deficiency

Background Because the mitochondrial respiratory chain (RC) is ubiquitous, its deficiency can theoretically give rise to any symptom in any organ or tissue at any age with any mode of inheritance, owing to the twofold genetic origin of respiratory enzyme machinery, that is, nuclear and mitochondrial. Not all respiratory enzyme deficiencies are primary and secondary or artefactual deficiency is frequently observed, leading to a number of misleading conclusions and inappropriate investigations in clinical practice. This study is aimed at investigating the potential role of brain MRI in distinguishing primary RC deficiency from phenocopies and other aetiologies. Methods Starting from a large series of 189 patients (median age: 3.5 years (8 days–56 years), 58% males) showing signs of RC enzyme deficiency, for whom both brain MRIs and disease-causing mutations were available, we retrospectively studied the positive predictive value (PPV) and the positive likelihood ratio (LR+) of brain MRI imaging and its ability to discriminate between two groups: primary deficiency of the mitochondrial RC machinery and phenocopies. Results Detection of (1) brainstem hyperintensity with basal ganglia involvement (P≤0.001) and (2) lactate peak with either brainstem or basal ganglia hyperintensity was highly suggestive of primary RC deficiency (P≤0.01). Fourteen items had a PPV>95%u2009and LR+ wasu2009greater than 9 for seven signs. Biallelic SLC19A3 mutations represented the main differential diagnosis. Non-significant differences between the two groups were found for cortical/subcortical atrophy, leucoencephalopathy and involvement of caudate nuclei, spinothalamic tract and corpus callosum. Conclusion Based on these results and owing to invasiveness of skeletal muscle biopsies and cost of high-throughput DNA sequencing, we suggest giving consideration to brain MRI imaging as a diagnostic marker and an informative investigation to be performed in patients showing signs of RC enzyme deficiency.

Autism spectrum disorders in propionic acidemia patients

Propionic acidemia is the result of a deficiency in propionyl-CoA carboxylase activity. Chronic neurologic and cognitive complications frequently occur, but the psychiatric evolution of the disorder is not well documented. We conducted a pedopsychiatric evaluation of 19 children, adolescents and young adults, aged between 2 and 25xa0years, using ADI-R, CARS-T, as well as ADOS when autism spectrum disorder was suspected. Previous psychometric examinations were also taken into consideration. Thirteen patients had an IQxa0<xa080. Two patients presented with autism and two additional patients with other autism spectrum disorders. Five patients did not fulfill diagnostic criteria for autism spectrum disorder but showed difficulties indicative of a broader autism phenotype (BAP). Four other patients had severe anxiety manifestations related to their disease. Two patients presented with acute psychotic episodes. The number of decompensations in the first 3xa0years of life was lower in patients with autism spectrum disorder or related symptoms. These patients were also older when they were assessed (median age of 15xa0years old versus 11xa0years old). There was no significant correlation between 3-hydroxypropionate levels during the first 6xa0years of life and autism spectrum disorder diagnosis. In conclusion, autism spectrum disorder is frequent in patients with propionic acidemia. These patients should undergo in-depth psychiatric evaluation and be screened for autism spectrum disorder. Further studies are needed to understand the underlying mechanisms.