Developmental epileptic encephalopathy in DLG4-related synaptopathy.

OBJECTIVE: The postsynaptic density protein of excitatory neurons PSD-95 is encoded by discs large MAGUK scaffold protein 4 (DLG4), de novo pathogenic variants of which lead to DLG4-related synaptopathy. The major clinical features are developmental delay, intellectual disability (ID), hypotonia, sleep disturbances, movement disorders, and epilepsy. Even though epilepsy is present in 50% of the individuals, it has not been investigated in detail. We describe here the phenotypic spectrum of epilepsy and associated comorbidities in patients with DLG4-related synaptopathy. METHODS: We included 35 individuals with a DLG4 variant and epilepsy as part of a multicenter study. The DLG4 variants were detected by the referring laboratories. The degree of ID, hypotonia, developmental delay, and motor disturbances were evaluated by the referring clinician. Data on awake and sleep electroencephalography (EEG) and/or video-polygraphy and brain magnetic resonance imaging were collected. Antiseizure medication response was retrospectively assessed by the referring clinician. RESULTS: A large variety of seizure types was reported, although focal seizures were the most common. Encephalopathy related to status epilepticus during slow-wave sleep (ESES)/developmental epileptic encephalopathy with spike-wave activation during sleep (DEE-SWAS) was diagnosed in >25% of the individuals. All but one individual presented with neurodevelopmental delay. Regression in verbal and/or motor domains was observed in all individuals who suffered from ESES/DEE-SWAS, as well as some who did not. We could not identify a clear genotype-phenotype relationship even between individuals with the same DLG4 variants. SIGNIFICANCE: Our study shows that a subgroup of individuals with DLG4-related synaptopathy have DEE, and approximately one fourth of them have ESES/DEE-SWAS. Our study confirms DEE as part of the DLG4-related phenotypic spectrum. Occurrence of ESES/DEE-SWAS in DLG4-related synaptopathy requires proper investigation with sleep EEG.

Expanding the clinical and molecular spectrum of FOXG1- and ZBTB18-associated neurodevelopmental disorders.

Introduction The zinc finger BTB domain-containing protein ZBTB18 binds to FOXG1 to form a transcriptional repressive complex involved in neuronal differentiation. Disruption of the components of this complex results in chromosome 1q43-q44 deletion syndrome/intellectual developmental disorder 22 or in FOXG1 syndrome. Case presentation This study reports on five patients with cognitive and behavioral impairment, seizures, microcephaly, and/or congenital brain abnormalities. Whole exome sequencing identified deleterious ZBTB18 variants in three patients and deleterious FOXG1 variants in the remaining patients. We have detected a missense variant within the BTB domain of ZBTB18 in two affected monozygotic twins. In addition, we observed agenesis of the septum pellucidum in a missense FOXG1 carrier with a severe FOXG1 syndrome. Conclusion Although the ZBTB18 zinc finger domains harbor the majority of known deleterious variants, we report a novel de novo rare missense variant within the BTB domain. The agenesis of the septum pellucidum observed in a missense FOXG1 carrier could be considered as a novel clinical feature associated with FOXG1 syndrome. The severe FOXG1 syndrome in this patient contrasts with the milder phenotype expected for a missense. Genetic or environmental factors may explain this phenotypic variability in FOXG1 syndrome.

Defining the clinical, molecular and imaging spectrum of adaptor protein complex 4-associated hereditary spastic paraplegia.

Bi-allelic loss-of-function variants in genes that encode subunits of the adaptor protein complex 4 (AP-4) lead to prototypical yet poorly understood forms of childhood-onset and complex hereditary spastic paraplegia: SPG47 (AP4B1), SPG50 (AP4M1), SPG51 (AP4E1) and SPG52 (AP4S1). Here, we report a detailed cross-sectional analysis of clinical, imaging and molecular data of 156 patients from 101 families. Enrolled patients were of diverse ethnic backgrounds and covered a wide age range (1.0-49.3 years). While the mean age at symptom onset was 0.8 ± 0.6 years [standard deviation (SD), range 0.2-5.0], the mean age at diagnosis was 10.2 ± 8.5 years (SD, range 0.1-46.3). We define a set of core features: early-onset developmental delay with delayed motor milestones and significant speech delay (50% non-verbal); intellectual disability in the moderate to severe range; mild hypotonia in infancy followed by spastic diplegia (mean age: 8.4 ± 5.1 years, SD) and later tetraplegia (mean age: 16.1 ± 9.8 years, SD); postnatal microcephaly (83%); foot deformities (69%); and epilepsy (66%) that is intractable in a subset. At last follow-up, 36% ambulated with assistance (mean age: 8.9 ± 6.4 years, SD) and 54% were wheelchair-dependent (mean age: 13.4 ± 9.8 years, SD). Episodes of stereotypic laughing, possibly consistent with a pseudobulbar affect, were found in 56% of patients. Key features on neuroimaging include a thin corpus callosum (90%), ventriculomegaly (65%) often with colpocephaly, and periventricular white-matter signal abnormalities (68%). Iron deposition and polymicrogyria were found in a subset of patients. AP4B1-associated SPG47 and AP4M1-associated SPG50 accounted for the majority of cases. About two-thirds of patients were born to consanguineous parents, and 82% carried homozygous variants. Over 70 unique variants were present, the majority of which are frameshift or nonsense mutations. To track disease progression across the age spectrum, we defined the relationship between disease severity as measured by several rating scales and disease duration. We found that the presence of epilepsy, which manifested before the age of 3 years in the majority of patients, was associated with worse motor outcomes. Exploring genotype-phenotype correlations, we found that disease severity and major phenotypes were equally distributed among the four subtypes, establishing that SPG47, SPG50, SPG51 and SPG52 share a common phenotype, an 'AP-4 deficiency syndrome'. By delineating the core clinical, imaging, and molecular features of AP-4-associated hereditary spastic paraplegia across the age spectrum our results will facilitate early diagnosis, enable counselling and anticipatory guidance of affected families and help define endpoints for future interventional trials.

Expanding the clinical and molecular spectrum of the CWC27-related spliceosomopathy.

Cyclophilins are a type of peptidyl-prolyl cis-trans isomerases. CWC27, one of the known human cyclophilins, is recruited by the spliceosome for the pre-mRNA splicing process. Biallelic deleterious variants in CWC27 lead to a spectrum of overlapping phenotypes including retinal degeneration, skeletal anomalies, short stature, and neurological defects. The present work reports a woman showing these clinical features, in addition to hypergonadotropic hypogonadism, hypoplastic/agenesic teeth, and cataracts, not previously associated with such phenotypic spectrum. Whole exome sequencing on this patient identified a novel CWC27 homozygous variant predicted to originate a severely truncated protein and the consequent loss of functionality. The clinical and genetic characterization of such patient could provide further insight into the underlying causes of the spliceosomopathies.

Comparison of the ABC and ACMG systems for variant classification.

The ABC and ACMG variant classification systems were compared by asking mainly European clinical laboratories to classify variants in 10 challenging cases using both systems, and to state if the variant in question would be reported as a relevant result or not as a measure of clinical utility. In contrast to the ABC system, the ACMG system was not made to guide variant reporting but to determine the likelihood of pathogenicity. Nevertheless, this comparison is justified since the ACMG class determines variant reporting in many laboratories. Forty-three laboratories participated in the survey. In seven cases, the classification system used did not influence the reporting likelihood when variants labeled as "maybe report" after ACMG-based classification were included. In three cases of population frequent but disease-associated variants, there was a difference in favor of reporting after ABC classification. A possible reason is that ABC step C (standard variant comments) allows a variant to be reported in one clinical setting but not another, e.g., based on Bayesian-based likelihood calculation of clinical relevance. Finally, the selection of ACMG criteria was compared between 36 laboratories. When excluding criteria used by less than four laboratories (<10%), the average concordance rate was 46%. Taken together, ABC-based classification is more clear-cut than ACMG-based classification since molecular and clinical information is handled separately, and variant reporting can be adapted to the clinical question and phenotype. Furthermore, variants do not get a clinically inappropriate label, like pathogenic when not pathogenic in a clinical context, or variant of unknown significance when the significance is known.

Trio-based exome sequencing reveals a high rate of the de novo variants in intellectual disability.

Intellectual disability (ID), a neurodevelopmental disorder affecting 1-3% of the general population, is characterized by limitations in both intellectual function and adaptive skills. The high number of conditions associated with ID underlines its heterogeneous origin and reveals the difficulty of obtaining a rapid and accurate genetic diagnosis. However, the Next Generation Sequencing, and the whole exome sequencing (WES) in particular, has boosted the diagnosis rate associated with ID. In this study, WES performed on 244 trios of patients clinically diagnosed with isolated or syndromic ID and their respective unaffected parents has allowed the identification of the underlying genetic basis of ID in 64 patients, yielding a diagnosis rate of 25.2%. Our results suggest that trio-based WES facilitates ID's genetic diagnosis, particularly in patients who have been extensively waiting for a definitive molecular diagnosis. Moreover, genotypic information from parents provided by trio-based WES enabled the detection of a high percentage (61.5%) of de novo variants inside our cohort. Establishing a quick genetic diagnosis of ID would allow early intervention and better clinical management, thus improving the quality of life of these patients and their families.