Search

PURPOSE Missense variants clustering in the BTB domain region of RHOBTB2 cause a developmental and epileptic encephalopathy (DEE) with early-onset seizures and severe intellectual disability. METHODS By international collaboration we assembled individuals with pathogenic RHOBTB2 variants and a variable spectrum of neurodevelopmental disorders (NDDs). By western blotting we investigated the consequences of missense variants in vitro. RESULTS In accordance with previous observations, de novo heterozygous missense variants in the BTB domain region led to a severe DEE in 16 individuals. We now identified also de novo missense variants in the GTPase domain in six individuals with apparently more variable neurodevelopmental phenotypes with or without epilepsy. In contrast to variants in the BTB domain region, variants in the GTPase domain do not impair proteasomal degradation of RHOBTB2 in vitro, indicating different functional consequences.Furthermore, we observed bi-allelic splice-site and truncating variants in nine families with variable neurodevelopmental phenotypes, indicating that complete loss of RHOBTB2 is pathogenic as well. CONCLUSION By identifying phenotype-genotype correlations regarding location and consequences of de novo missense variants in RHOBTB2 and by identifying bi-allelic truncating variants, we further delineate and expand the molecular and clinical spectrum of RHOBTB2 related disorders including both autosomal dominant and recessive NDDs.

Over a relatively short period of time, the clinical geneticist’s “toolbox” has been expanded by machine-learning algorithms for image analysis, which can be applied to the task of syndrome identification on the basis of facial photographs, but these technologies harbor potential beyond the recognition of established phenotypes. Here, we comprehensively characterized two individuals with a hitherto unknown genetic disorder caused by the same de novo mutation in LEMD2 (c.1436C>T;p.Ser479Phe), the gene which encodes the nuclear envelope protein LEM domain-containing protein 2 (LEMD2). Despite different ages and ethnic backgrounds, both individuals share a progeria-like facial phenotype and a distinct combination of physical and neurologic anomalies, such as growth retardation; hypoplastic jaws crowded with multiple supernumerary, yet unerupted, teeth; and cerebellar intention tremor. Immunofluorescence analyses of patient fibroblasts revealed mutation-induced disturbance of nuclear architecture, recapitulating previously published data in LEMD2-deficient cell lines, and additional experiments suggested mislocalization of mutant LEMD2 protein within the nuclear lamina. Computational analysis of facial features with two different deep neural networks showed phenotypic proximity to other nuclear envelopathies. One of the algorithms, when trained to recognize syndromic similarity (rather than specific syndromes) in an unsupervised approach, clustered both individuals closely together, providing hypothesis-free hints for a common genetic etiology. We show that a recurrent de novo mutation in LEMD2 causes a nuclear envelopathy whose prognosis in adolescence is relatively good in comparison to that of classical Hutchinson-Gilford progeria syndrome, and we suggest that the application of artificial intelligence to the analysis of patient images can facilitate the discovery of new genetic disorders.

As a result of a whole-exome sequencing study, we report three mutant alleles in SEC24D, a gene encoding a component of the COPII complex involved in protein export from the ER: the truncating mutation c.613C>T (p.Gln205∗) and the missense mutations c.3044C>T (p.Ser1015Phe, located in a cargo-binding pocket) and c.2933A>C (p.Gln978Pro, located in the gelsolin-like domain). Three individuals from two families affected by a similar skeletal phenotype were each compound heterozygous for two of these mutant alleles, with c.3044C>T being embedded in a 14 Mb founder haplotype shared by all three. The affected individuals were a 7-year-old boy with a phenotype most closely resembling Cole-Carpenter syndrome and two fetuses initially suspected to have a severe type of osteogenesis imperfecta. All three displayed a severely disturbed ossification of the skull and multiple fractures with prenatal onset. The 7-year-old boy had short stature and craniofacial malformations including macrocephaly, midface hypoplasia, micrognathia, frontal bossing, and down-slanting palpebral fissures. Electron and immunofluorescence microscopy of skin fibroblasts of this individual revealed that ER export of procollagen was inefficient and that ER tubules were dilated, faithfully reproducing the cellular phenotype of individuals with cranio-lentico-sutural dysplasia (CLSD). CLSD is caused by SEC23A mutations and displays a largely overlapping craniofacial phenotype, but it is not characterized by generalized bone fragility and presented with cataracts in the original family described. The cellular and morphological phenotypes we report are in concordance with the phenotypes described for the Sec24d-deficient fish mutants vbi (medaka) and bulldog (zebrafish).

Background : Krabbe disease (KD) is an inherited leukodystrophy due to a defect in the GALC gene which encodes the lysosomal galactosylceramide β-galactosidase (GALC). About two thirds of patients show the early onset form of KD dominated by cerebral demyelination leading to death in early infancy. Late onset forms include a spectrum of late infantile, juvenile and adult clinical courses. The deficiency of GALC leads to a galactosylceramide lipidosis in which lysosomal storage phenomena are seen almost only at the ultrastructural level. Results : In a 4-year-old boy, the clinical suspicion of KD was high according to neurologic and neuroimaging findings. However, laboratory results were inconclusive; white blood cell GALC activity being at 23 to 25% of the normal level, and GALC genotyping revealing the new homozygous p.Ala543Pro variant which, ex silico, was of unclear significance. Studying a skin biopsy, cultured fibroblasts showed the GALC activity at 21 to 30% of the normal level; ultrastructurally, clearly KD-specific inclusions were seen in the eccrine sweat gland cells, confirming a KD diagnosis. Conclusion : The high clinical suspicion combined with the morphologic evidence for KD predict that the p.Ala543Pro variant is pathogenic for (late onset) KD. A hypothesis linked to the proline in the mutant GALC may explain the in vitro effect with high residual GALC activity. This patient would not have been correctly diagnosed, despite the strong clinical criteria of KD, if the electron microscopic results had not been available. The detailed knowledge of neurologic and neuroimaging signs is important in diagnostically problematic KD patients in which also an electron microscopic approach can be crucial.

Objective To evaluate whether an early postnatal infection poses a long-term risk for neuropsychological impairment to neonates born very prematurely. Study design Adolescents born very preterm (n = 42, 11.6-16.2 years, mean = 13.9; 15 girls; 19 with and 23 without an early postnatal human cytomegalovirus [CMV] infection) and typically developing, term born controls (n = 24, 11.3-16.6 years, mean = 13.6; 12 girls) were neuropsychologically assessed with the German version of the Wechsler Intelligence Scale and the Developmental Test for Visual Perception. Results As expected, the full cohort of adolescents born preterm had significantly lower scores than term born controls on IQ (preterm: mean [SD] = 98.43 [14.83], control: 110.00 [8.10], P = .015) and on visuoperceptive abilities (95.64 [12.87] vs 106.24 [9.95], P = .016). Furthermore, adolescents born preterm with early postnatal CMV infection scored significantly lower than those without this infection regarding overall cognitive abilities (92.67 [14.71] vs 102.75 [13.67], P = .030), but not visuoperceptive abilities (91.22 [10.88] vs 98.96 [13.45], P > .05). Conclusions In our small but well-characterized group, our results provide evidence for adverse effects of early postnatal CMV infection on overall cognitive functions in adolescents born preterm. If confirmed, these results support the implementation of preventive measures.