Haploinsufficiency of ARFGEF1 is associated with developmental delay, intellectual disability, and epilepsy with variable expressivity

ADP ribosylation factor guanine nucleotide exchange factors (ARFGEFs) are a family of proteins implicated in cellular trafficking between the Golgi apparatus and the plasma membrane through vesicle formation. Among them is ARFGEF1/BIG1, a protein involved in axon elongation, neurite development, and polarization processes. ARFGEF1 has been previously suggested as a candidate gene for different types of epilepsies, although its implication in human disease has not been well characterized. International data sharing, in silico predictions, and in vitro assays with minigene study, western blot analyses, and RNA sequencing. We identified 13 individuals with heterozygous likely pathogenic variants in ARFGEF1. These individuals displayed congruent clinical features of developmental delay, behavioral problems, abnormal findings on brain magnetic resonance image (MRI), and epilepsy for almost half of them. While nearly half of the cohort carried de novo variants, at least 40% of variants were inherited from mildly affected parents who were clinically re-evaluated by reverse phenotyping. Our in silico predictions and in vitro assays support the contention that ARFGEF1-related conditions are caused by haploinsufficiency, and are transmitted in an autosomal dominant fashion with variable expressivity. We provide evidence that loss-of-function variants in ARFGEF1 are implicated in sporadic and familial cases of developmental delay with or without epilepsy

Clinical spectrum of MTOR-related hypomelanosis of Ito with neurodevelopmental abnormalities

PURPOSE: Hypomelanosis of Ito (HI) is a skin marker of somatic mosaicism. Mosaic MTOR pathogenic variants have been reported in HI with brain overgrowth. We sought to delineate further the pigmentary skin phenotype and clinical spectrum of neurodevelopmental manifestations of MTOR-related HI. METHODS: From two cohorts totaling 71 patients with pigmentary mosaicism, we identified 14 patients with Blaschko-linear and one with flag-like pigmentation abnormalities, psychomotor impairment or seizures, and a postzygotic MTOR variant in skin. Patient records, including brain magnetic resonance image (MRI) were reviewed. Immunostaining (n = 3) for melanocyte markers and ultrastructural studies (n = 2) were performed on skin biopsies. RESULTS: MTOR variants were present in skin, but absent from blood in half of cases. In a patient (p.[Glu2419Lys] variant), phosphorylation of p70S6K was constitutively increased. In hypopigmented skin of two patients, we found a decrease in stage 4 melanosomes in melanocytes and keratinocytes. Most patients (80%) had macrocephaly or (hemi)megalencephaly on MRI. CONCLUSION: MTOR-related HI is a recognizable neurocutaneous phenotype of patterned dyspigmentation, epilepsy, intellectual deficiency, and brain overgrowth, and a distinct subtype of hypomelanosis related to somatic mosaicism. Hypopigmentation may be due to a defect in melanogenesis, through mTORC1 activation, similar to hypochromic patches in tuberous sclerosis complex

De novo TBR1 variants cause a neurocognitive phenotype with ID and autistic traits:report of 25 new individuals and review of the literature

TBR1, a T-box transcription factor expressed in the cerebral cortex, regulates the expression of several candidate genes for autism spectrum disorders (ASD). Although TBR1 has been reported as a high-confidence risk gene for ASD and intellectual disability (ID) in functional and clinical reports since 2011, TBR1 has only recently been recorded as a human disease gene in the OMIM database. Currently, the neurodevelopmental disorders and structural brain anomalies associated with TBR1 variants are not well characterized. Through international data sharing, we collected data from 25 unreported individuals and compared them with data from the literature. We evaluated structural brain anomalies in seven individuals by analysis of MRI images, and compared these with anomalies observed in TBR1 mutant mice. The phenotype included ID in all individuals, associated to autistic traits in 76% of them. No recognizable facial phenotype could be identified. MRI analysis revealed a reduction of the anterior commissure and suggested new features including dysplastic hippocampus and subtle neocortical dysgenesis. This report supports the role of TBR1 in ID associated with autistic traits and suggests new structural brain malformations in humans. We hope this work will help geneticists to interpret TBR1 variants and diagnose ASD probands

The "extreme phenotype approach" applied to male breast cancer allows the identification of rare variants of ATR as potential breast cancer susceptibility alleles

In oncogenetics, some patients could be considered as "extreme phenotypes", such as those with very early onset presentation or multiple primary malignancies, unusually high numbers of cancers of the same spectrum or rare cancer types in the same parental branch. For these cases, a genetic predisposition is very likely, but classical candidate gene panel analyses often and frustratingly remains negative. In the framework of the EX2TRICAN project, exploring unresolved extreme cancer phenotypes, we applied exome sequencing on rare familial cases with male breast cancer, identifying a novel pathogenic variant of ATR (p.Leu1808*). ATR has already been suspected as being a predisposing gene to breast cancer in women. We next identified 3 additional ATR variants in a cohort of both male and female with early onset and familial breast cancers (c.7762-2A>C; c.2078+1G>A; c.1A>G). Further molecular and cellular investigations showed impacts on transcripts for variants affecting splicing sites and reduction of ATR expression and phosphorylation of the ATR substrate CHEK1. This work further demonstrates the interest of an extended genetic analysis such as exome sequencing to identify very rare variants that can play a role in cancer predisposition in extreme phenotype cancer cases unexplained by classical cancer gene panels testing

Recherche des bases moléculaires des phénotypes extrêmes de cancer par séquençage d'exome

Certains cancers peuvent être qualifiés de « phénotypes extrêmes ». Il s’agit soit de formes sporadiques particulièrement précoces, soit de formes familiales avec un excès de cancers dans une même branche parentale. La présence de plusieurs tumeurs primitives, de tumeurs bilatérales ou l'association de plusieurs cancers rares chez un même patient ou au sein d’une même famille, peut également entrer dans cette catégorie. Devant ces présentations, une prédisposition génétique est très fortement suspectée.L'analyse de panels de gènes connus pour être impliqués dans les formes mendéliennes de cancer est la pratique courante pour identifier la mutation responsable d'une prédisposition au cancer. Cependant, elle ne permet d’identifier la mutation responsable de la prédisposition génétique que dans 10% des cas. Il reste donc de nombreuses cas avec une prédisposition génétique au cancer indiscutable mais sans diagnostique moléculaire. Cela représente une difficulté majeure pour les oncogénéticiens souhaitant proposer une surveillance et un conseil génétique des plus adaptés aux patients et à leurs apparentés.Le séquençage de l’exome, de 27 patients présentant des phénotypes extrêmes de cancer, a permis d'identifier 9 gènes candidats pour une prédisposition génétique au cancer :- Trois de ces gènes candidats (ATR, DLC1 et TP53I3) ont été retrouvés à partir de cas familiaux de cancers du sein masculin, un cancer particulièrement rare. Le séquençage ciblé de ces gènes dans une cohorte de réplication a permis d’identifier des récurrences pour ATR et DLC1 et des analyses fonctionnelles ont permis de préciser la pathogénicité des certaines de ces variations.- Deux variations ont été identifiées dans des gènes déjà connus comme responsables de prédisposition génétique au cancer. L’une d’elle a été identifiée dans le gène PALB2 avec une localisation de cancer pulmonaire inhabituelle, diagnostiqué à 26 ans. La seconde est une variation hétérozygote du gène BLM dans un cancer de l’ovaire à 30 ans.- Les quatre autres variations candidates concernent des gènes impliqués dans les processus d’apoptose (BIK et DFFA), de régulation épigénétique (SETD2) ou de régulation de la prolifération cellulaire (FAT4).Ces résultats montrent la pertinence d'utiliser le séquençage d’exome et une approche de phénotypes extrêmes pour identifier des variations rares dans de nouveaux gènes candidats de prédisposition au cancer