Nathalie Boddaert

The ciliary gene RPGRIP1L is mutated in cerebello-oculo-renal syndrome (Joubert syndrome type B) and Meckel syndrome

Cerebello-oculo-renal syndrome (CORS), also called Joubert syndrome type B, and Meckel (MKS) syndrome belong to the group of developmental autosomal recessive disorders that are associated with primary cilium dysfunction. Using SNP mapping, we identified missense and truncating mutations in RPGRIP1L (KIAA1005) in both CORS and MKS, and we show that inactivation of the mouse ortholog Rpgrip1l (Ftm) recapitulates the cerebral, renal and hepatic defects of CORS and MKS. In addition, we show that RPGRIP1L colocalizes at the basal body and centrosomes with the protein products of both NPHP6 and NPHP4, known genes associated with MKS, CORS and nephronophthisis (a related renal disorder and ciliopathy). In addition, the RPGRIP1L missense mutations found in CORS individuals diminishes the interaction between RPGRIP1L and nephrocystin-4. Our findings show that mutations in RPGRIP1L can cause the multiorgan phenotypic abnormalities found in CORS or MKS, which therefore represent a continuum of the same underlying disorder.

High NPHP1 and NPHP6 Mutation Rate in Patients with Joubert Syndrome and Nephronophthisis: Potential Epistatic Effect of NPHP6 and AHI1 Mutations in Patients with NPHP1 Mutations

Joubert syndrome (JS) is an autosomal recessive disorder that is described in patients with cerebellar ataxia, mental retardation, hypotonia, and neonatal respiratory dysregulation. Kidney involvement (nephronophthisis or cystic renal dysplasia) is associated with JS in one fourth of known cases. Mutations in three genes--AHI1, NPHP1, and NPHP6--have been identified in patients with JS. However, because NPHP1 mutations usually cause isolated nephronophthisis, the factors that predispose to the development of neurologic involvement are poorly understood. In an attempt to identify such genetic determinants, a cohort of 28 families with nephronophthisis and at least one JS-related neurologic symptom were screened for mutations in AHI1, NPHP1, and NPHP6 genes. NPHP1 and NPHP6 homozygous or compound heterozygous mutations were found in 13 (46%) and six (21%) unrelated patients, respectively. Two of the 13 patients with NPHP1 mutations carried either a heterozygous truncating mutation in NPHP6 or a heterozygous missense mutation in AHI1. Furthermore, five patients with NPHP1 mutations carried the AHI1 variant R830W, which was predicted to be possibly damaging and was found with significantly higher frequency than in healthy control subjects and in patients with NPHP1 mutations without neurologic symptoms (five of 26 versus four of 276 and three of 152 alleles; P < 0.001 and P < 0.002, respectively). In contrast to the variable neurologic and milder retinal phenotype of patients with NPHP1 mutations, patients with NPHP6 mutations presented with a more severe neurologic and retinal phenotype. In conclusion, NPHP1 and NPHP6 are major genes of nephronophthisis associated with JS. Epistatic effects that are provided by heterozygous NPHP6 and AHI1 mutations and variants may contribute to the appearance of extrarenal symptoms in patients with NPHP1 mutations.

Histone H3F3A and HIST1H3B K27M mutations define two subgroups of diffuse intrinsic pontine gliomas with different prognosis and phenotypes

Diffuse intrinsic pontine glioma (DIPG) is the most severe paediatric solid tumour, with no significant therapeutic progress made in the past 50xa0years. Recent studies suggest that diffuse midline glioma, H3-K27M mutant, may comprise more than one biological entity. The aim of the study was to determine the clinical and biological variables that most impact their prognosis. Ninety-one patients with classically defined DIPG underwent a systematic stereotactic biopsy and were included in this observational retrospective study. Histone H3 genes mutations were assessed by immunochemistry and direct sequencing, whilst global gene expression profiling and chromosomal imbalances were determined by microarrays. A full description of the MRI findings at diagnosis and at relapse was integrated with the molecular profiling data and clinical outcome. All DIPG but one were found to harbour either a somatic H3-K27M mutation and/or loss of H3K27 trimethylation. We also discovered a novel K27M mutation in HIST2H3C, and a lysine-to-isoleucine substitution (K27I) in H3F3A, also creating a loss of trimethylation. Patients with tumours harbouring a K27M mutation in H3.3 (H3F3A) did not respond clinically to radiotherapy as well, relapsed significantly earlier and exhibited more metastatic recurrences than those in H3.1 (HIST1H3B/C). H3.3-K27M-mutated DIPG have a proneural/oligodendroglial phenotype and a pro-metastatic gene expression signature with PDGFRA activation, while H3.1-K27M-mutated tumours exhibit a mesenchymal/astrocytic phenotype and a pro-angiogenic/hypoxic signature supported by expression profiling and radiological findings. H3K27 alterations appear as the founding event in DIPG and the mutations in the two main histone H3 variants drive two distinct oncogenic programmes with potential specific therapeutic targets.

Refinement of cortical dysgeneses spectrum associated with TUBA1A mutations

Objective: We have recently shown that de novo mutations in the TUBA1A gene are responsible for a wide spectrum of neuronal migration disorders. To better define the range of these abnormalities, we searched for additional mutations in a cohort of 100 patients with lissencephaly spectrum for whom no mutation was identified in DCX, LIS1 and ARX genes and compared these data to five previously described patients with TUBA1A mutations. Results: We detected de novo TUBA1A mutations in six patients and highlight the existence of a prominent form of TUBA1A related lissencephaly. In four patients, the mutations identified, c.1190T>C (p.L397P), c.1265G>A (p.R422H), c.1264C>T (p.R422C), c.1306G>T (p.G436R), have not been reported before and in two others, the mutation corresponds to a recurrent missense mutation, c.790C>T (p.R264C), likely to be a hot spot of mutation. All together, it emerges that the TUBA1A related lissencephaly spectrum ranges from perisylvian pachygyria, in the less severe form, to posteriorly predominant pachygyria in the most severe, associated with dysgenesis of the anterior limb of the internal capsule and mild to severe cerebellar hypoplasia. When compared with a large series of lissencephaly of other origins (ILS17, ILSX or unknown origin), these features appear to be specific to TUBA1A related lissencephaly. In addition, TUBA1A mutated patients share a common clinical phenotype that consists of congenital microcephaly, mental retardation and diplegia/tetraplegia. Conclusions: Our data highlight the presence of consistent and specific abnormalities that should allow the differentiation of TUBA1A related lissencephalies from those related to LIS1, DCX and ARX genes.

Subtypes of Developmental Coordination Disorder: Research on Their Nature and Etiology

Children with Developmental Coordination Disorder (DCD) are a group embracing clumsiness and developmental dyspraxia. Our study provides a better understanding of the nature of DCD and its etiology, and identifies subtypes of dyspraxia. Forty-three children with DCD (5–15 years) were enrolled on the Diagnostic and Statistical Manual of Mental Disorders (4th ed. [DSM-IV-TR]; American Psychiatric Association, 2000) criteria. Extensive standardized evaluations were conducted. We distinguished from two patterns of “pure” developmental dyspraxia: ideomotor and visual-spatial/visual-constructional, and mix dyspraxia with more co-morbidities. Our study provides a better understanding of the nature of DCD, and sheds light on its etiology and brain dysfunction, so as to identify subtypes of developmental DCD/dyspraxia with specific clinical criteria.

Neurobehavioral Profile and Brain Imaging Study of the 22q13.3 Deletion Syndrome in Childhood

OBJECTIVE. The 22q13.3 deletion syndrome (Online Mendelian Inheritance in Man No. 606232) is a neurodevelopmental disorder that includes hypotonia, severely impaired development of speech and language, autistic-like behavior, and minor dysmorphic features. Although the number of reported cases is increasing, the 22q13.3 deletion remains underdiagnosed because of failure in recognizing the clinical phenotype and detecting the 22qter deletion by routine chromosome analyses. Our goal is to contribute to the description of the neurobehavioral phenotype and brain abnormalities of this microdeletional syndrome. METHODS. We assessed neuromotor, sensory, language, communication, and social development and performed cerebral MRI and study of regional cerebral blood flow measured by positron emission tomography in 8 children carrying the 22q13.3 deletion. RESULTS. Despite variability in expression and severity, the children shared a common developmental profile characterized by hypotonia, sleep disorders, and poor response to their environment in early infancy; expressive language deficit contrasting with emergence of social reciprocity from ages ∼3 to 5 years; sensory processing dysfunction; and neuromotor disorders. Brain MRI findings were normal or showed a thin or morphologically atypical corpus callosum. Positron emission tomography study detected a localized dysfunction of the left temporal polar lobe and amygdala hypoperfusion. CONCLUSIONS. The developmental course of the 22q13.3 deletion syndrome belongs to pervasive developmental disorders but is distinct from autism. An improved description of the natural history of this syndrome should help in recognizing this largely underdiagnosed condition.

Loss-of-function mutations in WDR73 are responsible for microcephaly and steroid-resistant nephrotic syndrome: Galloway-Mowat syndrome.

Galloway-Mowat syndrome is a rare autosomal-recessive condition characterized by nephrotic syndrome associated with microcephaly and neurological impairment. Through a combination of autozygosity mapping and whole-exome sequencing, we identified WDR73 as a gene in which mutations cause Galloway-Mowat syndrome in two unrelated families. WDR73 encodes a WD40-repeat-containing protein of unknown function. Here, we show that WDR73 was present in the brain and kidney and was located diffusely in the cytoplasm during interphase but relocalized to spindle poles and astral microtubules during mitosis. Fibroblasts from one affected child and WDR73-depleted podocytes displayed abnormal nuclear morphology, low cell viability, and alterations of the microtubule network. These data suggest that WDR73 plays a crucial role in the maintenance of cell architecture and cell survival. Altogether, WDR73 mutations cause Galloway-Mowat syndrome in a particular subset of individuals presenting with late-onset nephrotic syndrome, postnatal microcephaly, severe intellectual disability, and homogenous brain MRI features. WDR73 is another example of a gene involved in a disease affecting both the kidney glomerulus and the CNS.

The location of DCX mutations predicts malformation severity in X-linked lissencephaly

Lissencephaly spectrum (LIS) is one of the most severe neuronal migration disorders that ranges from agyria/pachygyria to subcortical band heterotopia. Approximately 80% of patients with the LIS spectrum carry mutations in either the LIS1 or DCX (doublecortin) genes which have an opposite gradient of severity. The aim of the study was to evaluate in detail the phenotype of DCX-associated lissencephaly and to look for genotype–phenotype correlations. Of the 180 male patients with DCX-related lissencephaly, 33 males (24 familial cases and nine cases with de novo mutations) were found with hemizygous DCX mutations and were clinically and genetically assessed here. DCX mutation analysis revealed that the majority of mutations were missense (79.2%), clustered in the two evolutionary conserved domains, N-DC and C-DC, of DCX. The most prominent radiological phenotype was an anteriorly predominant pachygyria or agyria (54.5%) although DCX-associated lissencephaly encompasses a complete range of LIS grades. The severity of neurological impairment was in accordance with the degree of agyria with severe cognitive impairment in all patients, inability to walk independently in over half and refractory epilepsy in more than a third. For genotype–phenotype correlations, patients were divided in two groups according to the location of DCX missense mutations. Patients with mutations in the C-DC domain tended to have a less severe lissencephaly (grade 4–5 in 58.3%) compared with those in the N-DC domain (grade 4–5 in 36.3%) although, in this dataset, this was not statistically significant (pu2009=u20090.12). Our evaluation suggests a putative correlation between phenotype and genotype. These data provide further clues to deepen our understanding of the function of the DCX protein and may give new insights into the molecular mechanisms that could influence the consequence of the mutation in the N-DC versus the C-DC domain of DCX.

Recessive and Dominant De Novo ITPR1 Mutations Cause Gillespie Syndrome.

Gillespie syndrome (GS) is a rare variant form of aniridia characterized by non-progressive cerebellar ataxia, intellectual disability, and iris hypoplasia. Unlike the more common dominant and sporadic forms of aniridia, there has been no significant association with PAX6 mutations in individuals with GS and the mode of inheritance of the disease had long been regarded as uncertain. Using a combination of trio-based whole-exome sequencing and Sanger sequencing in five simplex GS-affected families, we found homozygous or compound heterozygous truncating mutations (c.4672C>T [p.Gln1558(∗)], c.2182C>T [p.Arg728(∗)], c.6366+3A>T [p.Gly2102Valfs5(∗)], and c.6664+5G>T [p.Ala2221Valfs23(∗)]) and de novo heterozygous mutations (c.7687_7689del [p.Lys2563del] and c.7659T>G [p.Phe2553Leu]) in the inositol 1,4,5-trisphosphate receptor type 1 gene (ITPR1). ITPR1 encodes one of the three members of the IP3-receptors family that form Ca(2+) release channels localized predominantly in membranes of endoplasmic reticulum Ca(2+) stores. The truncation mutants, which encompass the IP3-binding domain and varying lengths of the modulatory domain, did not form functional channels when produced in a heterologous cell system. Furthermore, ITPR1 p.Lys2563del mutant did not form IP3-induced Ca(2+) channels but exerted a negative effect when co-produced with wild-type ITPR1 channel activity. In total, these results demonstrate biallelic and monoallelic ITPR1 mutations as the underlying genetic defects for Gillespie syndrome, further extending the spectrum of ITPR1-related diseases.

Neurological involvement in a child with atypical hemolytic uremic syndrome

We report the case of a 4-year-old boy, diagnosed with atypical hemolytic uremic syndrome (HUS) due to a hybrid factor H. He progressed to end-stage renal failure despite plasmatherapy and underwent bilateral nephrectomy because of uncontrolled hypertension. Three days after, he had partial complex seizures with normal blood pressure, normal blood count and normal magnetic resonance imaging (MRI), which recurred 1xa0month later. Eight months later, he had a third episode of seizures, with hemoglobin of 10xa0g/dl without schizocytes, low haptoglobin of 0.18xa0g/l, and moderate thrombocytopenia (platelets 98xa0×xa0109/l). He remained hypertensive and deeply confused for 2xa0days. The third MRI showed bilateral symmetrical hyperintensities of the cerebral pedunculas, caudate nuclei, putamens, thalami, hippocampi, and insulae suggesting thrombotic microangiopathy secondary to a relapse of HUS rather than reversible posterior leukoencephalopathy syndrome (RPLS), usually occipital and asymmetrical. Plasmatherapy led to a complete neurological recovery within 2xa0days although hypertension had remained uncontrolled. The fourth MRI 10xa0weeks after, on maintenance plasmatherapy, was normal and clinical examination remained normal, except for high blood pressure. In conclusion, brain MRI allows differentiating thrombotic microangiopathy lesions from RPLS in atypical HUS, which is crucial since lesions may be reversible with plasmatherapy.