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Microcephaly is a sign of many genetic conditions but has been rarely systematically evaluated. We therefore comprehensively studied the clinical and genetic landscape of an unselected cohort of patients with microcephaly. We performed clinical assessment, high-resolution chromosomal microarray analysis, exome sequencing, and functional studies in 62 patients (58% with primary microcephaly [PM], 27% with secondary microcephaly [SM], and 15% of unknown onset). We found severity of developmental delay/intellectual disability correlating with severity of microcephaly in PM, but not SM. We detected causative variants in 48.4% of patients and found divergent inheritance and variant pattern for PM (mainly recessive and likely gene-disrupting [LGD]) versus SM (all dominant de novo and evenly LGD or missense). While centrosome-related pathways were solely identified in PM, transcriptional regulation was the most frequently affected pathway in both SM and PM. Unexpectedly, we found causative variants in different mitochondria-related genes accounting for ~5% of patients, which emphasizes their role even in syndromic PM. Additionally, we delineated novel candidate genes involved in centrosome-related pathway (SPAG5, TEDC1), Wnt signaling (VPS26A, ZNRF3), and RNA trafficking (DDX1). Our findings enable improved evaluation and genetic counseling of PM and SM patients and further elucidate microcephaly pathways.

Four European Reference Networks (ERN-EYE, ERKNet, Endo-ERN, ERN-ITHACA) have teamed up to establish a consensus statement and recommendations for Bardet-Biedl syndrome (BBS). BBS is an autosomal recessive ciliopathy with at least 26 genes identified to date. The clinical manifestations are pleiotropic, can be observed in utero and will progress with age. Genetic testing has progressively improved in the last years prompting for a revision of the diagnostic criteria taking into account clinical Primary and Secondary features, as well as positive or negative molecular diagnosis. This consensus statement also emphasizes on initial diagnosis, monitoring and lifelong follow-up, and symptomatic care that can be provided to patients and family members according to the involved care professionals. For paediatricians, developmental anomalies can be at the forefront for diagnosis (such as polydactyly) but can require specific care, such as for associated neuro developmental disorders. For ophthalmology, the early onset retinal degeneration requires ad hoc functional and imaging technologies and specific care for severe visual impairment. For endocrinology, among other manifestations, early onset obesity and its complications has benefited from better evaluation of eating behaviour problems, improved lifestyle programs, and from novel pharmacological therapies. Kidney and urinary track involvements warrants lifespan attention, as chronic kidney failure can occur and early management might improve outcome. This consensus recommends revised diagnostic criteria for BBS that will ensure certainty of diagnosis, giving robust grounds for genetic counselling as well as in the perspective of future trials for innovative therapies.

Cas Simons, Ryan Taft and colleagues report the identification of KCNH1 mutations in six individuals with Temple-Baraitser syndrome (TBS). Electrophysiological measurements of cells expressing mutant KCNH1 channels show decreased activation thresholds and slower deactivation in comparison to wild-type channels, suggesting that these mutations lead to gain of function of KCNH1. Temple-Baraitser syndrome (TBS) is a multisystem developmental disorder characterized by intellectual disability, epilepsy, and hypoplasia or aplasia of the nails of the thumb and great toe 1 , 2 . Here we report damaging de novo mutations in KCNH1 (encoding a protein called ether à go-go, EAG1 or K V 10.1), a voltage-gated potassium channel that is predominantly expressed in the central nervous system (CNS), in six individuals with TBS. Characterization of the mutant channels in both Xenopus laevis oocytes and human HEK293T cells showed a decreased threshold of activation and delayed deactivation, demonstrating that TBS-associated KCNH1 mutations lead to deleterious gain of function. Consistent with this result, we find that two mothers of children with TBS, who have epilepsy but are otherwise healthy, are low-level (10% and 27%) mosaic carriers of pathogenic KCNH1 mutations. Consistent with recent reports 3 , 4 , 5 , 6 , 7 , 8 , this finding demonstrates that the etiology of many unresolved CNS disorders, including epilepsies, might be explained by pathogenic mosaic mutations.

Here we report a case of developmental and epileptic encephalopathy related to RHOBTB2 gene mutation in a ten‐month old infant in French Guiana. Although the 28 previously reported cases had early‐onset epilepsy and severe intellectual disability, here the reported individual presented with late postnatal onset of microcephaly and the absence of cortical atrophy on MRI. The publication of cases of such a rare form of developmental and epileptic encephalopathy will eventually allow us to better understand the mechanism by which RHOBTB2 misregulation could induce severe and atypical neurological disorders.

Purpose A few de novo missense variants in the cytoplasmic FMRP-interacting protein 2 ( CYFIP2 ) gene have recently been described as a novel cause of severe intellectual disability, seizures, and hypotonia in 18 individuals, with p.Arg87 substitutions in the majority. Methods We assembled data from 19 newly identified and all 18 previously published individuals with CYFIP2 variants. By structural modeling and investigation of WAVE-regulatory complex (WRC)-mediated actin polymerization in six patient fibroblast lines we assessed the impact of CYFIP2 variants on the WRC. Results Sixteen of 19 individuals harbor two previously described and 11 novel (likely) disease-associated missense variants. We report p.Asp724 as second mutational hotspot (4/19 cases). Genotype–phenotype correlation confirms a consistently severe phenotype in p.Arg87 patients but a more variable phenotype in p.Asp724 and other substitutions. Three individuals with milder phenotypes carry putative loss-of-function variants, which remain of unclear pathogenicity. Structural modeling predicted missense variants to disturb interactions within the WRC or impair CYFIP2 stability. Consistent with its role in WRC-mediated actin polymerization we substantiate aberrant regulation of the actin cytoskeleton in patient fibroblasts. Conclusion Our study expands the clinical and molecular spectrum of CYFIP2 -related neurodevelopmental disorder and provides evidence for aberrant WRC-mediated actin dynamics as contributing cellular pathomechanism.

Whole-gene duplications and missense variants in the HUWE1 gene (NM_031407.6) have been reported in association with intellectual disability (ID). Increased gene dosage has been observed in males with non-syndromic mild to moderate ID with speech delay. Missense variants reported previously appear to be associated with severe ID in males and mild or no ID in obligate carrier females. Here, we report the largest cohort of patients with HUWE1 variants, consisting of 14 females and 7 males, with 15 different missense variants and one splice site variant. Clinical assessment identified common clinical features consisting of moderate to profound ID, delayed or absent speech, short stature with small hands and feet and facial dysmorphism consisting of a broad nasal tip, deep set eyes, epicanthic folds, short palpebral fissures, and a short philtrum. We describe for the first time that females can be severely affected, despite preferential inactivation of the affected X chromosome. Three females with the c.329 G  >  A p.Arg110Gln variant, present with a phenotype of mild ID, specific facial features, scoliosis and craniosynostosis, as reported previously in a single patient. In these females, the X inactivation pattern appeared skewed in favour of the affected transcript. In summary, HUWE1 missense variants may cause syndromic ID in both males and females.

Defects in optic fissure closure can lead to congenital ocular coloboma. This ocular malformation, often associated with microphthalmia, is described in various clinical forms with different inheritance patterns and genetic heterogeneity. In recent times, the identification of an increased number of genes involved in numerous cellular functions has led to a better understanding in optic fissure closure mechanisms. Nevertheless, most of these genes are also involved in wider eye growth defects such as micro-anophthalmia, questioning the mechanisms controlling both extension and severity of optic fissure closure defects. However, some genes, such as FZD5, have only been so far identified in isolated coloboma. Thus, to estimate the frequency of implication of different ocular genes, we screened a cohort of 50 patients affected by ocular coloboma by using targeted sequencing of 119 genes involved in ocular development. This analysis revealed seven heterozygous (likely) pathogenic variants in RARB, MAB21L2, RBP4, TFAP2A, and FZD5. Surprisingly, three out of the seven variants detected herein were novel disease-causing variants in FZD5 identified in three unrelated families with dominant inheritance. Although molecular diagnosis rate remains relatively low in patients with ocular coloboma (14% (7/50) in this work), these results, however, highlight the importance of genetic screening, especially of FZD5, in such patients. Indeed, in our series, FZD5 variants represent half of the genetic causes, constituting 6% (3/50) of the patients who benefited from a molecular diagnosis. Our findings support the involvement of FZD5 in ocular coloboma and provide clues for screening this gene during current diagnostic procedures.

Cardio-facio-cutaneous (CFC) syndrome is characterized by a distinctive facial appearance, heart defects and mental retardation. It phenotypically overlaps with Noonan and Costello syndrome, which are caused by mutations in PTPN11 and HRAS , respectively. In 43 individuals with CFC, we identified two heterozygous KRAS mutations in three individuals and eight BRAF mutations in 16 individuals, suggesting that dysregulation of the RAS-RAF-ERK pathway is a common molecular basis for the three related disorders.

Valérie Cormier-Daire and colleagues report the identification of mutations in SMAD4 that cause Myhre syndrome, a developmental disorder characterized by short stature, short hands and feet, facial dysmorphism, muscular hypertrophy, deafness and cognitive delay. All of the mutations alter a single codon in the Mad Homology 2 domain of SMAD4. Myhre syndrome (MIM 139210) is a developmental disorder characterized by short stature, short hands and feet, facial dysmorphism, muscular hypertrophy, deafness and cognitive delay. Using exome sequencing of individuals with Myhre syndrome, we identified SMAD4 as a candidate gene that contributes to this syndrome on the basis of its pivotal role in the bone morphogenetic pathway (BMP) and transforming growth factor (TGF)-β signaling. We identified three distinct heterozygous missense SMAD4 mutations affecting the codon for Ile500 in 11 individuals with Myhre syndrome. All three mutations are located in the region of SMAD4 encoding the Mad homology 2 (MH2) domain near the site of monoubiquitination at Lys519, and we found a defect in SMAD4 ubiquitination in fibroblasts from affected individuals. We also observed decreased expression of downstream TGF-β target genes, supporting the idea of impaired TGF-β–mediated transcriptional control in individuals with Myhre syndrome.

Background Data on clinical manifestations of neurofibromatosis-Noonan syndrome (NF-NS) remain heterogeneous, with limited validated descriptions. Methods This study aims to better define the clinical and molecular features of NF-NS and compare them with existing literature. Secondary objectives include evaluating inter-rater diagnostic agreement among experienced clinicians and assessing the utility of deep-learning algorithms (Face2Gene ® [F2G]). Additionally, we assess the prevalence of congenital heart malformations (CHM) in NF-NS compared to ‘classic’ neurofibromatosis type 1 (NF1). A 9-year, prospective, monocentric study was conducted, involving patients with NF1 pathogenic variants (PVs) and Noonan syndrome-like facial phenotype (NSLFP). Results Twenty-six patients were enrolled. NSLFP was categorized as ‘suggestive’ in 69% of cases and ‘typical’ in 31%. The presence of at least two facial abnormalities (e.g., low-set ears, downslanted palpebral fissures, hypertelorism, and ptosis) was consistently observed in ‘typical’ cases. Inter-rater concordance was substantial (0.65 [95% CI = 0.56; 0.74]), while concordance between clinicians and F2G was almost perfect at (0.821 [CI 95% = 0.625; 1.000]). Missense NF1 PVs were observed in 38.5% of cases. Apart from NSLP and a high frequency of pectus excavatum (62.5%), no significant differences in anthropometric, dermatological, neurological, skeletal, or ocular clinical features were observed between NF-NS and ‘classic’ NF1. CHM were found in 19.2% of NF-NS patients, with pulmonic stenosis present in 7.7%. Conclusion NF-NS is a distinct phenotypic variant of NF1, marked by NSLP with consistent facial features -, and frequent pectus excavatum. F2G demonstrated high diagnostic concordance, reinforcing its clinical utility. Given the elevated risk of CHM, especially pulmonic stenosis, proactive cardiovascular assessment similar to other RASopathies is recommended for NS-NF patients, regardless of NF1 PV type.