Tubulin, one of the most abundant cytoskeletal building blocks, has numerous isotypes in metazoans encoded by different conserved genes. Whether these distinct isotypes form cell type– and context-specific microtubule structures is poorly understood. Based on a cohort of 12 patients with primary ciliary dyskinesia as well as mouse mutants, we identified and characterized variants in the TUBB4B isotype that specifically perturbed centriole and cilium biogenesis. Distinct TUBB4B variants differentially affected microtubule dynamics and cilia formation in a dominant-negative manner. Structure-function studies revealed that different TUBB4B variants disrupted distinct tubulin interfaces, thereby enabling stratification of patients into three classes of ciliopathic diseases. These findings show that specific tubulin isotypes have distinct and nonredundant subcellular functions and establish a link between tubulinopathies and ciliopathies.

Bartter (BS) and Gitelman (GS) syndrome are autosomal recessive inherited tubulopathies, whose clinical diagnosis can be challenging, due to rarity and phenotypic overlap. Genotype–phenotype correlations have important implications in defining kidney and global outcomes. The aim of our study was to assess the diagnostic rate of whole-exome sequencing (WES) coupled with a bioinformatic analysis of copy number variations in a population of 63 patients with BS and GS from a single institution, and to explore genotype-phenotype correlations. We obtained a diagnostic yield of 86% (54/63 patients), allowing disease reclassification in about 14% of patients. Although some clinical and laboratory features were more commonly reported in patients with BS or GS, a significant overlap does exist, and age at onset, preterm birth, gestational age and nephro-calcinosis are frequently misleading. Finally, chronic kidney disease (CKD) occurs in about 30% of patients with BS or GS, suggesting that the long-term prognosis can be unfavorable. In our cohort the features associated with CKD were lower gestational age at birth and a molecular diagnosis of BS, especially BS type 1. The results of our study demonstrate that WES is useful in dealing with the phenotypic heterogeneity of these disorders, improving differential diagnosis and genotype-phenotype correlation.

Oculocutaneous albinism is an autosomal recessive disorder characterized by the presence of typical ocular features, such as foveal hypoplasia, iris translucency, hypopigmented fundus oculi and reduced pigmentation of skin and hair. Albino patients can show significant clinical variability; some individuals can present with only mild depigmentation and subtle ocular changes. Here, we provide a retrospective review of the standardized clinical charts of patients firstly addressed for evaluation of foveal hypoplasia and slightly subnormal visual acuity, whose diagnosis of albinism was achieved only after extensive phenotypic and genotypic characterization. Our report corroborates the pathogenicity of the two common TYR polymorphisms p.(Arg402Gln) and p.(Ser192Tyr) when both are located in trans with a pathogenic TYR variant and aims to expand the phenotypic spectrum of albinism in order to increase the detection rate of the albino phenotype. Our data also suggest that isolated foveal hypoplasia should be considered a clinical sign instead of a definitive diagnosis of an isolated clinical entity, and we recommend deep phenotypic and molecular characterization in such patients to achieve a proper diagnosis.

BACKGROUND: Anemia is the most frequent cytopenia in myelodysplastic syndromes (MDS), neoplastic diseases characterized by ineffective hematopoiesis and bone marrow dysplasia. MDS usually affect elderly individuals (median age in Italy 74 years), and quite rarely concern younger patients. It is of increasing interest to verify whether "young", not therapy-related MDS patients carry germline (GM) predisposition, in order to optimize therapeutic and transplant choices. The best approach is to perform Whole Exome Sequencing (WES) instead of targeted next-generation sequencing (t-NGS) panel in cases in which MDS patients have no syndromic signs or any indicative sign of predisposing alterations. AIM: We considered a cohort of 21 consecutive MDS cases with age at diagnosis < 60 years and anemia, referred to our MDS Unit for a second opinion. METHODS: After bone marrow (BM) re-evaluation and morphological confirmation of dysplasia compatible with MDS, we screened the 21 MDS patients by WES on BM-DNA or peripheral blood DNA (PB-DNA). For DNA sequencing, DNA libraries were sequenced using the NextSeq 550 Illumina System. Variant calling was carried out using GATK caller. T-NGS myeloid panel was in some cases applied to confirm somatic nature of mutations. Samples of 5/21 MDS patients and their relatives were further analyzed after WES by applying high-coverage t-NGS 86-gene custom panel for hereditary anemias on PB-DNA. WES of DNA extracted from saliva (S-DNA) samples was performed to provide a GM confirmation. In order to confirm pathogenic role in red blood cell (RBC) membrane defects of identified variants, we also performed the ektacytometry analysis that evaluates the erythrocyte deformability and the hydration status by subjecting them to an increasing osmotic gradient with constant shear stress. RESULTS: Five of 21 MDS cases (23.8%) with symptomatic anemia (3 MDS-MLD, 1 MDS-SLD, 1 MDS with isolated del5q) were identified as carriers of variants suspected responsible of RBC membrane defects in both BM/PB-DNA and S-DNA samples, where no other germline myeloid predisposing alterations were demonstrated. MDS-associated somatic variants were present in 4/5 patients (KRAS, TET2, CBL, SRSF2, U2AF1, IDH2, with VAF >25 %). High coverage t-NGS analysis confirmed the presence of a heterozygous rare missense variant in PIEZO1 in probands 1 and 5; a heterozygous rare missense variant in PIEZO1 and ANK1 in proband 2; a heterozygous rare missense variant in PIEZO1 and SPTA1 in proband 3; a complex mode of inheritance in proband 4 with causative variants in G6PD, KCCN4, SPTB, and ABCB6 genes. PIEZO1 or KCNN4 gene variants result in erythrocyte dehydration and determine dehydrated hereditary stomatocytosis (DHS). Ektacytometry analysis showed a significant difference in the osmolarity curve of these patients, confirming the pathogenic role of the variants identified. Among these MDS suspected cases, only proband 4 was diagnostically re-categorized because of lack of acquired recurrent somatic mutations and presence of multiple alterations in erythroid genes causing dysplasia of erythroid precursors, masquerading as MDS. None of the patients presented a history of unexplained anemia before the onset of MDS, consistent with what shown for DHS1 patients with well-compensated hemolysis. Inheritance pattern of the identified variants according the study of the families confirmed the segregation of the pathogenic variants. CONCLUSION: Onset of de novo MDS in unusually young age should always prompt investigation of predisposing conditions. We suggest here that co-existence of inherited RBC membrane defects with MDS may determine earlier clinical manifestation of the clonal disease. Hereditary anemias, in particular xerocytosis, may mimic MDS morphology. In our study, among the 5 "young" MDS with concomitant inherited RBC membrane defect, one case did not finally confirm MDS diagnosis by karyotype or NGS myeloid mutation analysis. This case fulfilled the diagnostic criteria for combined hereditary hemolytic anemia: DHS2, G6PD deficiency, spherocytosis, familial pseudohyperkalemia 2, with multi-locus mode of inheritance that justifies the clinical condition (splenomegaly, hemolytic crisis, ascites). Addition of genetic testing for hereditary anemias beside assessment of germline predisposing variants may allow a more precise diagnosis in controversial cases of "young" MDS.

Context: Cytochrome C oxidase (COX) is the fourth component of the respiratory chain and is located within the internal membrane of mitochondria. COX deficiency causes an inherited mitochondrial disease with significant genetic and phenotypic heterogeneity. Four clinical subtypes have been identified, each with distinct phenotypes and genetic variants. Mitochondrial complex IV deficiency nuclear type 4 (MC4DN4) is a form of COX deficiency associated with pathogenic variants in the SCO1 gene. Case description: We describe three patients with MC4DN4 with developmental and epileptic encephalopathy (DEE), hypopituitarism, and SCO1 pathogenic variants. These patients’ phenotypes considerably differ from previously reported MC4DN4 phenotypes as they associate DEE with progressive hypopituitarism and survival beyond the first months after birth. Pituitary deficiency in these patients progressively worsened and mainly involved growth hormone secretion and thyroid function. Conclusions: Our findings expand knowledge of phenotypic variability in MC4DN4 and suggest that SCO1 is a candidate gene for genetic hypopituitarism and DEE. Significance statement: Our paper describes three patients affected by MC4DN4 with hypopituitarism and developmental and epileptic encephalopathy (DEE), two features that have never been associated with this condition. In addition, we reviewed the clinical features of all previous cases of MC4DN4 to give the other clinicians a wide picture of the clinical phenotype of this genetic disease. We hope that the publication of our data may help others to identify this disease and consider the chance to analyze the SCO1 gene in cases of DEE associated with pituitary dysfunction. Our article contributes to expanding the spectrum of genetic hypopituitarism and proposes a model to explain an association between this condition, mitochondrial anomalies, and neurodevelopmental defects.

Purpose: To describe the long-term, multimodal follow-up and multidisciplinary evaluation of two pediatric patients with CDH3-related retinopathy, discussing the genotypic and phenotypic spectrum of this rare cadherinopathy. Design: Retrospective observational case series. Methods: Two unrelated children with early-onset macular dystrophy and congenital hypotrichosis underwent a comprehensive ophthalmic examination, including spectral-domain optical coherence tomography (SD-OCT), blue-light fundus autofluorescence (BAF), microperimetry, and full-field electroretinography (ffERG), combined with dermatologic assessment and exome sequencing. Follow-up extended over 4 years in Patient 1 and 15 years in Patient 2. Results: Both patients showed sharply demarcated posterior pole chorioretinal atrophy with preservation of the peripheral retina and stable best-corrected visual acuity throughout follow-up. Microperimetry documented localized sensitivity loss with limited progression. SD-OCT revealed persistent ellipsoid zone disruption, retinal pigment epithelium atrophy, and outer retinal tubulations. Dermatologic evaluation confirmed congenital hypotrichosis without nail abnormalities; one patient exhibited mild fifth finger clinodactyly. Genetic testing identified the following two distinct homozygous CDH3 variants: a splice-site mutation (c.160+1G>A) and a frameshift insertion (c.1837dup, p.(Asp613Glyfs*4)). Conclusions:CDH3 retinopathy presents with a characteristic multimodal imaging pattern of localized macular atrophy and slow functional decline associated with congenital hypotrichosis. A comprehensive multidisciplinary approach was essential for the correct diagnosis and a better and more thorough definition of the clinical presentation. Detailed long-term follow-up supports the hypothesis of retinal pigment epithelium dysfunction or maldevelopment rather than widespread retinal degeneration. Recognition of this phenotype is critical for accurate diagnosis, genetic counseling, and future gene-therapy strategies targeting the preserved peripheral retina.