Juliette Piard

Novel comprehensive diagnostic strategy in Pitt–Hopkins syndrome: Clinical score and further delineation of the TCF4 mutational spectrum

Pitt–Hopkins syndrome (PTHS), characterized by severe intellectual disability and typical facial gestalt, is part of the clinical spectrum of Rett‐like syndromes. TCF4, encoding a basic helix‐loop‐helix (bHLH) transcription factor, was identified as the disease‐causing gene with de novo molecular defects. While PTHS appears to be a recognizable clinical entity, it seems to remain underdiagnosed, especially when facial gestalt is less typical. With the aim to facilitate the diagnosis of PTHS and to increase its rate and specificity, we have investigated 33 novel patients and defined a Clinical Diagnosis Score. Analysis of 112 individuals (79 previously reported and 33 novel patients) allowed us to delineate the TCF4 mutational spectrum, with 40% point mutations, 30% small deletions/insertions, and 30% deletions. Most of these were private mutations and generated premature stop codons. Missense mutations were localized in the bHLH domain, which is a mutational hotspot. No obvious difference was observed between patients harboring truncating, missense mutations, or deletions, further supporting TCF4 haploinsufficiency as the molecular mechanism underlying PTHS. In this study, we have summarized the current knowledge of TCF4 molecular pathology, reported all the mutations in the TCF4 database (http://www.LOVD.nl/TCF4), and present a novel and comprehensive diagnostic strategy for PTHS. Hum Mutat 33:64–72, 2012.

De novo mutations of KIAA2022 in females cause intellectual disability and intractable epilepsy

Background Mutations in the KIAA2022 gene have been reported in male patients with X-linked intellectual disability, and related female carriers were unaffected. Here, we report 14 female patients who carry a heterozygous de novo KIAA2022 mutation and share a phenotype characterised by intellectual disability and epilepsy. Methods Reported females were selected for genetic testing because of substantial developmental problems and/or epilepsy. X-inactivation and expression studies were performed when possible. Results All mutations were predicted to result in a frameshift or premature stop. 12 out of 14 patients had intractable epilepsy with myoclonic and/or absence seizures, and generalised in 11. Thirteen patients had mild to severe intellectual disability. This female phenotype partially overlaps with the reported male phenotype which consists of more severe intellectual disability, microcephaly, growth retardation, facial dysmorphisms and, less frequently, epilepsy. One female patient showed completely skewed X-inactivation, complete absence of RNA expression in blood and a phenotype similar to male patients. In the six other tested patients, X-inactivation was random, confirmed by a non-significant twofold to threefold decrease of RNA expression in blood, consistent with the expected mosaicism between cells expressing mutant or normal KIAA2022 alleles. Conclusions Heterozygous loss of KIAA2022 expression is a cause of intellectual disability in females. Compared with its hemizygous male counterpart, the heterozygous female disease has less severe intellectual disability, but is more often associated with a severe and intractable myoclonic epilepsy.

Severe sex differentiation disorder in a boy with a 3.8 Mb 10q25.3–q26.12 microdeletion encompassing EMX2

The molecular basis of male disorders of sex development (DSD) remains unexplained in a large number of cases. EMX2 has been proposed to play a role in the masculinization process for the past two decades, but formal evidence for this causal role is scarce. The aim of this study is to yield additional support to this hypothesis by reporting on a male patient who presented with 46,XY DSD, a single kidney, intellectual disability, and the smallest microdeletion including EMX2 reported to date. EMX2 haploinsufficiency is likely to explain the masculinization defect observed in our patient, similar to what has been described in the mouse. In the case of cytogenetically diagnosed cases, deletions of EMX2 have been associated with a wide range of DSD, ranging from hypospadias to complete sex reversal.

DYRK1A mutations in two unrelated patients.

The Dual-specify tyrosine phosphorylation-regulated kinase 1A (DYRK1A) gene has been extensively studied for its role in the pathophysiology of intellectual disability (ID) in Down syndrome. The rise of next generation sequencing (NGS) and array-CGH (aCGH) in diagnostic settings for the evaluation of patients with ID allowed the identification of 17 patients carrying heterozygous genetic aberrations involving DYRK1A to date. The rate of DYRK1A mutations in this population reaches >1% in published NGS studies. The current report aims at further defining the phenotype of this encephalopathy with the detailed report of two unrelated patients. Both patients were boys with developmental delay, febrile seizures, facial dysmorphism and brain atrophy on MRI. Patient #1 had autistic behaviors and micropenis and Patient #2 had stereotypies and microcephaly. NGS analyses identified heterozygous de novo variants in DYRK1A: the c.613C >T (p.Arg205*) nonsense mutation in Patient #1 and the c.932C >T (p.Ser311Phe) missense mutation in Patient #2. Together with previously reported cases, patients with DYRK1A mutations share many clinical features and may have a recognizable phenotype that includes, by decreasing order of frequency: developmental delay or ID with behaviors suggesting autism spectrum disorder, microcephaly, epileptic seizures, facial dysmorphism including ear anomalies (large ears, hypoplastic lobes), thin lips, short philtrum and frontal bossing. Delineation of the phenotype/genotype correlation is not feasible at the moment and will be a challenge for the coming years.

Mutations in GREB1L Cause Bilateral Kidney Agenesis in Humans and Mice

Congenital anomalies of the kidney and urinary tract (CAKUT) constitute a major cause of chronic kidney disease in children and 20% of prenatally detected anomalies. CAKUT encompass a spectrum of developmental kidney defects, including renal agenesis, hypoplasia, and cystic and non-cystic dysplasia. More than 50 genes have been reported as mutated in CAKUT-affected case subjects. However, the pathophysiological mechanisms leading to bilateral kidney agenesis (BKA) remain largely elusive. Whole-exome or targeted exome sequencing of 183 unrelated familial and/or severe CAKUT-affected case subjects, including 54 fetuses with BKA, led to the identification of 16 heterozygous variants in GREB1L (growth regulation by estrogen in breast cancer 1-like), a gene reported as a target of retinoic acid signaling. Four loss-of-function and 12 damaging missense variants, 14 being absent from GnomAD, were identified. Twelve of them were present in familial or simplex BKA-affected case subjects. Female BKA-affected fetuses also displayed uterus agenesis. We demonstrated a significant association between GREB1L variants and BKA. By in situ hybridization, we showed expression of Greb1l in the nephrogenic zone in developing mouse kidney. We generated a Greb1l knock-out mouse model by CRISPR-Cas9. Analysis at E13.5 revealed lack of kidneys and genital tract anomalies in male and female Greb1l-/- embryos and a slight decrease in ureteric bud branching in Greb1l+/- embryos. We showed that Greb1l invalidation in mIMCD3 cells affected tubulomorphogenesis in 3D-collagen culture, a phenotype rescued by expression of the wild-type human protein. This demonstrates that GREB1L plays a major role in early metanephros and genital development in mice and humans.

Intragenic deletion of UBE3A gene in 2 sisters with Angelman syndrome detected by MLPA.

Intragenic Deletion of UBE3A Gene in 2 Sisters With Angelman Syndrome Detected by MLPA Juliette Piard,* Christel Depienne, Boris Keren, Estelle F edirko, Oriane Trouillard, Perrine Charles, and Delphine Heron Unit e Fonctionnelle de G en etique M edicale AP-HP, D epartement de G en etique et Cytog en etique, Centre de R ef erence «D eficiences Intellectuelles de Causes Rares», Groupe Hospitalier CRicm, UMR-S975 (Ex-U679), Piti e-Salpêtri ere, Paris, France Centre de G en etique Humaine, Universit e de Franche-Comt e, CHU Besançon, Besançon, France Unit e Fonctionnelle de Neurog en etique Mol eculaire et Cellulaire, AP-HP, D epartement de G en etique et Cytog en etique, Centre de G en etique Mol eculaire, Hôpital de la Piti e-Salpêtri ere, Paris, France CRicm, UMR-S975 (Ex-U679), Universit e Pierre et Marie Curie-Paris 6, Paris, France Unit e Fonctionnelle de Cytog en etique, AP-HP, D epartement de G en etique et Cytog en etique, F ed eration de G en etique, Hôpital de la Piti e-Salpêtri ere, Paris, France

TCF12 microdeletion in a 72-year-old woman with intellectual disability.

Heterozygous mutations in TCF12 were recently identified as an important cause of craniosynostosis. In the original series, 14% of patients with a mutation in TCF12 had significant developmental delay or learning disability. We report on the first case of TCF12 microdeletion, detected by array‐comparative genomic hybridization, in a 72‐year‐old patient presenting with intellectual deficiency and dysmorphism. Multiplex ligation‐dependent probe amplification analysis indicated that exon 19, encoding the functionally important basic helix‐loop‐helix domain, was included in the deleted segment in addition to exon 20. We postulate that the TCF12 microdeletion is responsible for this patients intellectual deficiency and facial phenotype.

POLG2 deficiency causes adult-onset syndromic sensory neuropathy, ataxia and parkinsonism.

Mitochondrial dysfunction plays a key role in the pathophysiology of neurodegenerative disorders such as ataxia and Parkinsons disease. We describe an extended Belgian pedigree where seven individuals presented with adult‐onset cerebellar ataxia, axonal peripheral ataxic neuropathy, and tremor, in variable combination with parkinsonism, seizures, cognitive decline, and ophthalmoplegia. We sought to identify the underlying molecular etiology and characterize the mitochondrial pathophysiology of this neurological syndrome.

A homozygous ATAD1 mutation impairs postsynaptic AMPA receptor trafficking and causes a lethal encephalopathy

Members of the AAA+ superfamily of ATPases are involved in the unfolding of proteins and disassembly of protein complexes and aggregates. ATAD1 encoding the ATPase family, AAA+ domain containing 1-protein Thorase plays an important role in the function and integrity of mitochondria and peroxisomes. Postsynaptically, Thorase controls the internalization of excitatory, glutamatergic AMPA receptors by disassembling complexes between the AMPA receptor-binding protein, GRIP1, and the AMPA receptor subunit GluA2. Using whole-exome sequencing, we identified a homozygous frameshift mutation in the last exon of ATAD1 [c.1070_1071delAT; p.(His357Argfs*15)] in three siblings who presented with a severe, lethal encephalopathy associated with stiffness and arthrogryposis. Biochemical and cellular analyses show that the C-terminal end of Thorase mutant gained a novel function that strongly impacts its oligomeric state, reduces stability or expression of a set of Golgi, peroxisomal and mitochondrial proteins and affects disassembly of GluA2 and Thorase oligomer complexes. Atad1-/- neurons expressing Thorase mutantHis357Argfs*15 display reduced amount of GluA2 at the cell surface suggesting that the Thorase mutant may inhibit the recycling back and/or reinsertion of AMPA receptors to the plasma membrane. Taken together, our molecular and functional analyses identify an activating ATAD1 mutation as a new cause of severe encephalopathy and congenital stiffness.

Cutis laxa and excessive bone growth due to de novo mutations in PTDSS1

The cutis laxa syndromes are multisystem disorders that share loose redundant inelastic and wrinkled skin as a common hallmark clinical feature. The underlying molecular defects are heterogeneous and 13 different genes have been involved until now, all of them being implicated in elastic fiber assembly. We provide here molecular and clinical characterization of three unrelated patients with a very rare phenotype associating cutis laxa, facial dysmorphism, severe growth retardation, hyperostotic skeletal dysplasia, and intellectual disability. This disorder called Lenz–Majewski syndrome (LMS) is associated with gain of function mutations in PTDSS1, encoding an enzyme involved in phospholipid biosynthesis. This report illustrates that LMS is an unequivocal cutis laxa syndrome and expands the clinical and molecular spectrum of this group of disorders. In the neonatal period, brachydactyly and facial dysmorphism are two early distinctive signs, later followed by intellectual disability and hyperostotic skeletal dysplasia with severe dwarfism allowing differentiation of this condition from other cutis laxa phenotypes. Further studies are needed to understand the link between PTDSS1 and extra cellular matrix assembly.