Blindness affects the developmental trajectory of the sleeping brain.

Sleep plays a crucial role in brain development, sensory information processing, and consolidation. Sleep spindles are markers of these mechanisms as they mirror the activity of the thalamocortical circuits. Spindles can be subdivided into two groups, slow (10-13 Hz) and fast (13-16 Hz), which are each associated with different functions. Specifically, fast spindles oscillate in the high-sigma band and are associated with sensorimotor processing, which is affected by visual deprivation. However, how blindness influences spindle development has not yet been investigated. We recorded nap video-EEG of 50 blind/severely visually impaired (BSI) and 64 sighted children aged 5 months to 6 years old. We considered aspects of both macro- and micro-structural spindles. The BSI children lacked the evolution of developmental spindles within the central area. Specifically, young BSI children presented low central high-sigma and high-beta (25-30 Hz) event-related spectral perturbation and showed no signs of maturational decrease. High-sigma and high-beta activity in the BSI group correlated with clinical indices predicting perceptual and motor disorders. Our findings suggest that fast spindles are pivotal biomarkers for identifying an early developmental deviation in BSI children. These findings are critical for initial therapeutic intervention.

Novel molecular, structural and clinical findings in an Italian cohort of congenital cataract.

The current genetic diagnostic workup of congenital cataract (CC) is mainly based on NGS panels, whereas exome sequencing (ES) has occasionally been employed. In this multicentre study, we investigated by ES the detection yield, mutational spectrum and genotype-phenotype correlations in a CC cohort recruited between 2020 and mid-2022. The cohort consisted of 67 affected individuals from 51 unrelated families and included both non-syndromic (75%) and syndromic (25%) phenotypes, with extra-CC ocular/visual features present in both groups (48% and 76%, respectively). The functional effect of variants was predicted by 3D modelling and hydropathy properties changes. Variant clustering was used for the in-depth assessment of genotype-phenotype correlations. A diagnostic (pathogenic or likely pathogenic) variant was identified in 19 out of 51 probands/families (~37%). In a further 14 probands/families a candidate variant was identified: in 12 families a VUS was detected, of which 9 were considered plausibly pathogenic (i.e., 4 or 5 points according to ACMG criteria), while in 2 probands ES identified a single variant in an autosomal recessive gene associated with CC. Eighteen probands/families, manifesting primarily non-syndromic CC (15/18, 83%), remained unsolved. The identified variants (8 P, 12 LP, 10 VUS-PP, and 5 VUS), half of which were unreported in the literature, affected five functional categories of genes involved in transcription/splicing, lens formation/homeostasis (i.e., crystallin genes), membrane signalling, cell-cell interaction, and immune response. A phenotype-specific variant clustering was observed in four genes (KIF1A, MAF, PAX6, SPTAN1), whereas variable expressivity and potential phenotypic expansion in two (BCOR, NHS) and five genes (CWC27, KIF1A, IFIH1, PAX6, SPTAN1), respectively. Finally, ES allowed to detect variants in six genes not commonly included in commercial CC panels. These findings broaden the genotype-phenotype correlations in one of the largest CC cohorts tested by ES, providing novel insights into the underlying pathogenetic mechanisms and emphasising the power of ES as first-tier test.

LZTFL1, a rare cause of Bardet-Biedl syndrome: A new patient with severe short stature and moderate intellectual disability, more than casual associations?

Bardet-Biedl syndrome (BBS) is an inherited ciliopathy affecting multiple organs and systems with wide clinical and genetic heterogeneity. To date, biallelic variants of the LZTFL1 gene have been reported only in six patients with BBS. We identified a homozygous LZTFL1 nonsense variant in a boy presenting with classical BBS features. In addition, he showed a more pronounced cognitive impairment than previously reported subjects and severe short stature, matching the phenotype displayed by some other patients with LZTFL1 variants and lztfl1 knock-out mice. This case report contributes to a better understanding of the clinical spectrum associated with LZTFL1 pathogenic variants, and highlights possible genotype-phenotype correlations.

Visual function in children with Joubert syndrome.

AIM: To describe visual function in children with Joubert syndrome and to investigate its possible association with diagnostic and developmental aspects. METHOD: This retrospective cross-sectional work included 59 patients (33 male; mean age 9 years 2 months, standard deviation 6 years 3 months, range 4 months to 23 years) diagnosed with Joubert syndrome from January 2002 to December 2020. Data about clinical (neurological, neuro-ophthalmological, developmental/cognitive) and diagnostic (e.g. genetic testing, neuroimaging, systemic involvement) evaluations were collected in a data set during a review of medical records. Clinical and diagnostic variables were described in terms of raw counts and percentages. A χ2 test was conducted to investigate their association with neuropsychological skills. RESULTS: Ocular motor apraxia was highly represented in our cohort (75%), with a high prevalence of refractive defects and retinal abnormalities. Developmental delay/intellectual disability was frequent (in 69.5% of the sample), associated with retinal dystrophy (p = 0.047) and reduced visual acuity both for near (p = 0.014) and for far distances (p = 0.017). INTERPRETATION: On the basis of the relevance of oculomotor and perceptual alterations and their impact on overall and cognitive impairment, we encourage early and multidisciplinary assessment and follow-up of visual function in children with Joubert syndrome. This would help in planning a personalized rehabilitation to sustain functional vision. Further studies will be important to explore the link between biological aspects and global functioning in children with Joubert syndrome. WHAT THIS PAPER ADDS: Perceptual deficits and oculomotor impairments frequently coexist in Joubert syndrome. Retinal dysfunction may be present despite the absence of funduscopic abnormalities. Both perceptual and oculomotor impairments negatively affect cognitive development in Joubert syndrome.

Recurrent, founder and hypomorphic variants contribute to the genetic landscape of Joubert syndrome.

BACKGROUND: Joubert syndrome (JS) is a neurodevelopmental ciliopathy characterised by a distinctive mid-hindbrain malformation, the 'molar tooth sign'. Over 40 JS-associated genes are known, accounting for two-thirds of cases. METHODS: While most variants are novel or extremely rare, we report on 11 recurring variants in seven genes, including three known 'founder variants' in the Ashkenazi Jewish, Hutterite and Finnish populations. We evaluated variant frequencies in ~550 European patients with JS and compared them with controls (>15 000 Italian plus gnomAD), and with an independent cohort of ~600 JS probands from the USA. RESULTS: All variants were markedly enriched in the European JS cohort compared with controls. When comparing allele frequencies in the two JS cohorts, the Ashkenazim founder variant (TMEM216 c.218G>T) was significantly enriched in American compared with European patients with JS, while MKS1 c.1476T>G was about 10 times more frequent among European JS. Frequencies of other variants were comparable in the two cohorts. Genotyping of several markers identified four novel European founder haplotypes.Two recurrent variants (MKS1 c.1476T>G and KIAA0586 c.428delG), have been detected in homozygosity in unaffected individuals, suggesting they could act as hypomorphic variants. However, while fibroblasts from a MKS1 c.1476T>G healthy homozygote showed impaired ability to form primary cilia and mildly reduced ciliary length, ciliary parameters were normal in cells from a KIAA0586 c.428delG healthy homozygote. CONCLUSION: This study contributes to understand the complex genetic landscape of JS, explain its variable prevalence in distinct geographical areas and characterise two recurrent hypomorphic variants.

SUFU haploinsufficiency causes a recognisable neurodevelopmental phenotype at the mild end of the Joubert syndrome spectrum.

BACKGROUND: Joubert syndrome (JS) is a recessively inherited ciliopathy characterised by congenital ocular motor apraxia (COMA), developmental delay (DD), intellectual disability, ataxia, multiorgan involvement, and a unique cerebellar and brainstem malformation. Over 40 JS-associated genes are known with a diagnostic yield of 60%-75%.In 2018, we reported homozygous hypomorphic missense variants of the SUFU gene in two families with mild JS. Recently, heterozygous truncating SUFU variants were identified in families with dominantly inherited COMA, occasionally associated with mild DD and subtle cerebellar anomalies. METHODS: We reanalysed next generation sequencing (NGS) data in two cohorts comprising 1097 probands referred for genetic testing of JS genes. RESULTS: Heterozygous truncating and splice-site SUFU variants were detected in 22 patients from 17 families (1.5%) with strong male prevalence (86%), and in 8 asymptomatic parents. Patients presented with COMA, hypotonia, ataxia and mild DD, and only a third manifested intellectual disability of variable severity. Brain MRI showed consistent findings characterised by vermis hypoplasia, superior cerebellar dysplasia and subtle-to-mild abnormalities of the superior cerebellar peduncles. The same pattern was observed in two out of three tested asymptomatic parents. CONCLUSION: Heterozygous truncating or splice-site SUFU variants cause a novel neurodevelopmental syndrome encompassing COMA and mild JS, which likely represent overlapping entities. Variants can arise de novo or be inherited from a healthy parent, representing the first cause of JS with dominant inheritance and reduced penetrance. Awareness of this condition will increase the diagnostic yield of JS genetic testing, and allow appropriate counselling about prognosis, medical monitoring and recurrence risk.

Superior Cerebellar Atrophy: An Imaging Clue to Diagnose ITPR1-Related Disorders.

The inositol 1,4,5-triphosphate receptor type 1 (ITPR1) gene encodes an InsP3-gated calcium channel that modulates intracellular Ca2+ release and is particularly expressed in cerebellar Purkinje cells. Pathogenic variants in the ITPR1 gene are associated with different types of autosomal dominant spinocerebellar ataxia: SCA15 (adult onset), SCA29 (early-onset), and Gillespie syndrome. Cerebellar atrophy/hypoplasia is invariably detected, but a recognizable neuroradiological pattern has not been identified yet. With the aim of describing ITPR1-related neuroimaging findings, the brain MRI of 14 patients with ITPR1 variants (11 SCA29, 1 SCA15, and 2 Gillespie) were reviewed by expert neuroradiologists. To further evaluate the role of superior vermian and hemispheric cerebellar atrophy as a clue for the diagnosis of ITPR1-related conditions, the ITPR1 gene was sequenced in 5 patients with similar MRI pattern, detecting pathogenic variants in 4 of them. Considering the whole cohort, a distinctive neuroradiological pattern consisting in superior vermian and hemispheric cerebellar atrophy was identified in 83% patients with causative ITPR1 variants, suggesting this MRI finding could represent a hallmark for ITPR1-related disorders.

Allocentric spatial perception through vision and touch in sighted and blind children.

Vision and touch play a critical role in spatial development, facilitating the acquisition of allocentric and egocentric frames of reference, respectively. Previous works have shown that children's ability to adopt an allocentric frame of reference might be impaired by the absence of visual experience during growth. In the current work, we investigated whether visual deprivation also impairs the ability to shift from egocentric to allocentric frames of reference in a switching-perspective task performed in the visual and haptic domains. Children with and without visual impairments from 6 to 13 years of age were asked to visually (only sighted children) or haptically (blindfolded sighted children and blind children) explore and reproduce a spatial configuration of coins by assuming either an egocentric perspective or an allocentric perspective. Results indicated that temporary visual deprivation impaired the ability of blindfolded sighted children to switch from egocentric to allocentric perspective more in the haptic domain than in the visual domain. Moreover, results on visually impaired children indicated that blindness did not impair allocentric spatial coding in the haptic domain but rather affected the ability to rely on haptic egocentric cues in the switching-perspective task. Finally, our findings suggested that the total absence of vision might impair the development of an egocentric perspective in case of body midline-crossing targets.

Impaired urinary concentration ability is a sensitive predictor of renal disease progression in Joubert syndrome.

BACKGROUND: Joubert syndrome (JS) is an inherited ciliopathy characterized by a complex midbrain-hindbrain malformation and multiorgan involvement. Renal disease, mainly juvenile nephronophthisis (NPH), was reported in 25-30% patients although only ∼18% had a confirmed diagnosis of chronic kidney disease (CKD). NPH often remains asymptomatic for many years, resulting in delayed diagnosis. The aim of the study was to identify a biomarker able to quantify the risk of progressive CKD in young children with JS. METHODS: Renal features were investigated in 93 Italian patients, including biochemical tests, ultrasound and 1-deamino-8D-arginine vasopressin test in children with reduced basal urine osmolality. A subset of patients was followed-up over time. RESULTS: At last examination, 27 of 93 subjects (29%) presented with CKD, ranging from isolated urinary concentration defect (UCD) to end-stage renal disease. Both normal and pathological urine osmolality levels remained stable over time, even when obtained at very early ages. Follow-up data showed that the probability of developing CKD can be modelled as a function of the urine osmolality value, exceeding 75% for levels <600 mOsm/kg H2O, and significantly increased in patients with an early diagnosis of isolated UCD. CONCLUSIONS: We conclude that the frequency of CKD in JS increases with age and is higher than previously reported. Urine osmolality represents an early sensitive quantitative biomarker of the risk of CKD progression.

Visual Function Classification System for children with cerebral palsy: development and validation.

AIM: To develop and validate the Visual Function Classification System (VFCS), which was created to classify how children with cerebral palsy (CP) use visual abilities in daily life. METHOD: The process of development and validation of the VFCS involved four phases: (1) drafting of the five levels from the analysis of literature and clinical experience; (2) validation of constructs and revision of the levels for concept meaningfulness, using nominal group process; (3) refinement by international Delphi survey; and(4) assessment of interrater reliability among professionals and with caregivers, and of test-retest reliability. RESULTS: Five nominal groups involved 29 participants; 65 people completed the first round and 51 the second round of the Delphi survey. Construct validity was demonstrated within an expert group and external validation through several stakeholders, with the involvement of patients and families to ensure meaningfulness of the concept. Discussions continued until consensus was reached about the construct and content of the five levels. Participants in the reliability study included 29 professionals, 39 parents, and a total sample of 160 children with CP (mean age [SD] 6y 6mo [3y 4mo]; median 5y 7mo, range 1-19y). Absolute interrater agreement among professionals was 86% (weighted κ=0.88; 95% confidence interval [CI] 0.83-0.93). Test-retest reliability was high (weighted κ=0.97; 95% CI 0.95-0.99). Parent-professional interrater reliability on 39 children was moderate (weighted κ=0.51; 95% CI 0.39-0.63). INTERPRETATION: The VFCS has been appropriately constructed and provides a reliable system to classify visual abilities of children with CP both in clinical and in research settings. WHAT THIS PAPER ADDS: The Visual Function Classification System is a valid and reliable system. It classifies visual abilities of children with cerebral palsy in clinical and research settings. At a clinical level, it can be used to harmonize communication among professionals and identify patients' strengths and weaknesses. In research settings, it can be used to stratify patients, define natural history evolution, and interpret intervention studies.

SISTEMA DE CLASIFICACIÓN DE LA FUNCIÓN VISUAL PARA NIÑOS CON PARÁLISIS CEREBRAL: DESARROLLO Y VALIDACIÓN: OBJETIVO: Desarrollar y validar el Sistema de Clasificación de la Función Visual (VFCS, siglas en inglés), que fue creado para clasificar cómo los niños con parálisis cerebral (PC) usan las habilidades visuales en la vida diaria. MÉTODO: El proceso de desarrollo y validación del VFCS involucró cuatro fases: (1) elaboración de los cinco niveles a partir del análisis de la literatura y la experiencia clínica; (2) la validación de constructos y la revisión de los niveles para el significado de los conceptos, utilizando un proceso de grupo nominal; (3) refinamiento por encuesta internacional de Delphi; (4) evaluación de la confiabilidad entre evaluadores entre profesionales y con los cuidadores, y de confiabilidad de prueba y reevaluación RESULTADOS: Cinco grupos nominales incluyeron 29 participantes; 65 personas completaron la primera ronda y 51 la segunda ronda de la encuesta de Delphi. La validez de constructo se demostró dentro de un grupo de expertos y una validación externa a través de varias partes interesadas, con la participación de los pacientes y las familias para garantizar el significado del concepto. Las discusiones continuaron hasta que se llegó a un consenso sobre el constructo y el contenido de los cinco niveles. Los participantes en el estudio de confiabilidad incluyeron 29 profesionales, 39 padres y una muestra total de 160 niños con PC (edad media [DS] 6 años 6 meses [3 años 4 meses]; mediana 5 años 7 meses, rango 1-19 años). El acuerdo de evaluador absoluto entre profesionales fue del 86% (κ ponderada = 0,88; intervalo de confianza del 95% [IC] 0,83-0,93). La fiabilidad de Test-Retest fue alta (κ ponderada = 0,97; IC del 95%: 0,95 a 0,99). La confiabilidad entre los padres y profesionales entre 39 niños fue moderada (ponderada κ = 0,51; IC del 95%: 0,39 a 0,63). INTERPRETACIÓN: El VFCS se ha construido de manera adecuada y proporciona un sistema confiable para clasificar las habilidades visuales de los niños con PC, tanto en el ámbito clínico como en el de investigación.

SISTEMA DE CLASSIFICAÇÃO DA FUNÇÃO VISUAL PARA CRIANÇAS COM PARALISIA CEREBRAL: DESENVOLVIMENTO E VALIDAÇÃO: OBJETIVO: Desenvolver e validar o Sistema de Classificação da Função Visual (SCFV), que foi criado para classificar como crianças com paralisia cerebral (PC) usam capacidades visuais na vida diária. MÉTODO: O processo de desenvolvimento e validação do SCFV envolve quatro fases: (1) rascunho dos cinco níveis a partir da análise da literatura e experiência clínica; (2) validação de construtos e revisão dos níveis de significância dos conceitos, usando processo nominal de grupos; (3) refinamento por meio de levantamento Delphi internacional; (4) avaliação da confiabilidade inter-examinadores entre profissionais e cuidadores, e confiabilidade teste-reteste. RESULTADOS: Cinco grupos nominais envolveram 29 participantes; 65 pessoas completaram a primeira rodada e 51 a segunda rodada do levantamento Delphi. A validade de constructo foi demonstrada em um grupo de especialistas, e a validade externa por meio de vários interessados, com envolvimento de pacientes e famílias para assegurar a significância do conceito. As discussões continuaram até que fosse atingido consenso sobre o constructo e o conteúdo dos cinco níveis. Os participantes no estudo de confiabilidade incluíram 29 profissionais, 39 pais e uma amostra total de 160 crianças com PC (média de idade [DP] 6a 6m [3a 4m]; mediana 5a 7m, variação 1-19a). A confiabilidade inter-examinadores absoluta entre profissionais foi 86% (κ ponderado=0,88; intervalo de confiança [IC] a 95% 0,83-0,93). A confiabilidade teste-reteste foi alta (κ ponderado =0,97; IC 95% 0,95-0,99). A confiabilidade inter-examinadores pais-profissionais em 39 crianças foi moderada (κ ponderado =0,51; IC 95% 0,39-0,63). INTERPRETAÇÃO: O SCFV foi elaborado apropriadamente e é um sistema confiável para classificar as capacidades visuais de crianças com PC em ambientes clínicos e acadêmicos.