Background: Abnormal sodium-dependent hexose reabsorption in the proximal tubule, accompanied by a functional decrease in sodium and water reabsorption under conditions of increased volemia, may be attributed to a dysfunction of primary transporters related to a genetic defect in the Na,K-ATPase gamma subunit. Methods: We examined two sisters, aged 6 and 8 years, who presented with hypercalciuria, glucosuria, fructosuria, galactosuria, and atypical proteinuria. Primary diabetes, galactosemia, and fructosemia were excluded, suggesting a defect in cellular hexose transport in the proximal tubule. We conducted tests on the family members to assess the impact of gradually increasing volemia, using a water-loading test, on tubular H⁺ transport and urinary excretion of calcium, citrate, endothelin-1 (ET-1), and atypical proteins. Whole-exome sequencing was performed in the affected patients to identify the genetic basis of this phenotype. Results: Extended investigations revealed a complex defect in tubular H⁺ transport, calcium and citrate handling, and atypical proteinuria, resulting from water load-driven overproduction of endothelin-1 (ET-1). Genetic analysis identified a heterozygous pathogenic variant, c.80G>A, p.(Arg27His), in the FXYD2 gene, which encodes the gamma subunit of sodium/potassium-transporting ATPase. Conclusions: Our findings provide evidence that a defect in FXYD2 (splice form a) leads to functional impairment of proximal tubular hexose reabsorption. This is the first report on the metabolic consequences of a pathogenic FXYD2 variant affecting the gamma subunit of sodium/potassium-transporting ATPase in humans. The genotype–phenotype correlation in two siblings with a sodium-dependent defect in fructose, galactose, and glucose renal reabsorption allowed us to characterize a disease with a distinct clinical course and biochemical profile, not previously reported in the medical literature or genetic databases. Analysis of this condition was crucial for the early introduction of reno-protective treatment aimed at slowing the progression of nephropathy and for risk assessment in family members, which was essential for genetic counseling.

Introduction: Epilepsy syndromes show marked clinical and genetic heterogeneity, with numerous functionally diverse genes involved in their etiology. Next-generation sequencing (NGS) has facilitated the identification of many monogenic epilepsy syndromes and enables earlier, more accurate diagnosis in pediatric patients. Materials and Methods: This study analyzes the molecular profiles of 87 pediatric patients with various forms of epilepsy in whom pathogenic or likely pathogenic variants were identified. Next-generation sequencing (NGS) using multi-gene epilepsy panels or whole-exome sequencing (WES) was performed. Results: A total of 88 pathogenic or likely pathogenic variants were detected in 48 epilepsy-related genes; 30 variants occurred de novo. SCN1A and KCNQ2 were the most frequent contributors (12.6% and 9.2%, respectively). The highest percentage of positive diagnoses (48%) was observed in patients with developmental and epileptic encephalopathy (DEE), with variants identified in genes including ALG13, ATP1A2, CACNA1A, CDKL5, CHD2, GABRG2, ITPA, KCNQ2, PCDH19, SCN1A, SCN2A, SCN3A, SCN8A, SMC1A, SPTAN1, STXBP1, and UBA5. Pathogenic variants in ANKRD11 were found in four patients with KBG syndrome, while other genes appeared sporadically. Conclusions: Targeted massively parallel sequencing is an effective diagnostic tool for pediatric epilepsy. The presence of numerous single-case findings highlights the high genetic heterogeneity of epilepsy. This approach enabled more precise diagnoses that would not have been achieved through clinical evaluation alone, underscoring the importance of genetic testing for prognosis and treatment planning in pediatric patients with unexplained epilepsy.

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Background: PURA-related neurodevelopmental disorder (PURA-NDD; OMIM #616158) is a rare autosomal dominant condition caused by pathogenic variants in the PURA gene encoding Purα, a multifunctional protein involved in DNA replication, transcriptional regulation, and RNA transport. Since its initial description in 2014, PURA-NDD has been increasingly recognized as a distinct clinical entity with early onset and a broad phenotypic spectrum. The clinical presentation is characterized primarily by neonatal hypotonia, global developmental delay, intellectual disability, feeding difficulties, and epilepsy, along with additional features such as respiratory insufficiency, movement disorders, hypersomnolence, and variable dysmorphic traits. Despite a relatively recognizable core phenotype, marked inter-individual variability often limits the ability to establish a definitive clinical diagnosis based on phenotype alone. This underscores the essential role of molecular genetic testing in the differential diagnosis of rare neurodevelopmental disorders. Patients and methods: We report a cohort of eight individuals (four males and four females) aged 17 months to 15.5 years with PURA-related neurodevelopmental disorder (PURA-NDD), evaluated using a genotype-first diagnostic strategy supported by comprehensive genomic testing, including next-generation sequencing (NGS) panels and whole-genome sequencing (WGS). Patients were referred for the evaluation of nonspecific neurodevelopmental features, including neonatal hypotonia, respiratory distress, and epilepsy, in the absence of a definitive clinical diagnosis. Results: Molecular analysis identified eight heterozygous variants in PURA, of which four (50%) were novel: c.311T>G p.(Met104Arg), c.406_407del p.(Gln136Glyfs64), c.515A>C p.(Gln172Pro), and c.885delinsGC p.(His296Profs21). The remaining variants included previously reported missense and frameshift changes associated with PURA-NDD, as well as one variant previously reported in ClinVar. Conclusions: Our findings not only confirm the core clinical features of PURA-related neurodevelopmental disorder but also contribute to a more comprehensive delineation of its phenotypic spectrum. The detailed characterization of our cohort broadens the range of recognized clinical manifestations and further highlights the marked phenotypic heterogeneity of PURA-NDD. In addition, the identification of both novel and previously reported pathogenic variants expands the mutational spectrum of PURA and underscores the importance of integrating clinical, molecular, and bioinformatic data for accurate variant interpretation. Although genotype–phenotype correlations remain incompletely understood, emerging evidence suggests potential associations between variant type or location and clinical severity, warranting further investigation in larger cohorts. The recognition of characteristic neonatal features may facilitate earlier diagnosis and implementation of supportive multidisciplinary management. Overall, this study illustrates how genomic technologies not only improve diagnostic yield in rare disorders but also refine disease definition, enhance the understanding of underlying pathogenic mechanisms, and support the development of more precise genotype–phenotype correlations. Further studies involving larger cohorts and long-term follow-up are needed to better define the full clinical and molecular spectrum of PURA-NDD.

Background: Rubinstein–Taybi syndrome (RSTS) is characterized by intellectual disability, short stature, distinctive facial dysmorphism, broad thumbs/halluces, hearing loss, congenital heart or renal defects, and cryptorchidism in males. Pathogenic variants in CREBBP (~90% of cases) or EP300 (~10%) underlie the disorder, with ~88% single nucleotide variants (SNVs) and ~12% copy number variants (CNVs) in CREBBP. Materials and Methods: We investigated 17 patients clinically diagnosed with RSTS at a tertiary hospital in Poland. Genetic confirmation was achieved by next-generation sequencing, multiplex ligation-dependent probe amplification (MLPA), array comparative genomic hybridization (aCGH), or Sanger sequencing. Results: Pathogenic variants were identified in CREBBP (13/17, 76%) and EP300 (4/17, 24%). Variant types included frameshift indels (6/17, 35%), missense (4/17, 24%), nonsense (3/17, 18%), splice-site (2/17, 12%), and gross deletions (2/17, 12%). Notably, 13/17 (76%) were novel: ten in CREBBP (c.−49_12del, c.289C>T, c.1093_1096del, c.1094A>G, c.3178A>T, c.3401A>T, c.(3836+1_3837−1)_(4394+1_4395−1)del, c.4133+2T>G, c.4963dup, c.5028_5029dup) and three in EP300 (c.1942C>T, c.3044_3045del, c.4713_4722del). Among the novel CREBBP variants, eight occurred de novo and two had unknown inheritance. Two novel EP300 variants occurred de novo and one was of unknown origin. Conclusions: This first Polish RSTS cohort demonstrates a considerable proportion of gross deletions (12% overall; 15% in CREBBP) and an unexpectedly high rate of novel variants (76%), suggesting possible population-specific differences. These findings underscore the genetic heterogeneity of RSTS and highlight the importance of comprehensive molecular diagnostics and studies in underrepresented populations.

Not available Keywords: Birk-Barel syndrome KCNK9 gene imprinting disorders channelopathy