ABSTRACTVariants in the phosphoribosylpyrophosphate synthetase (PRPS1) gene have been shown to cause X‐linked nonsyndromic hearing loss (HL) (DFNX1) in humans. A c.259G>A transition in PRPS1, which leads to p.Ala87Thr, has been demonstrated to cause HL. The aim of this study was to generate a transgenic knock‐in (KI) mouse with the Prps1 missense variant p.Ala87Thr and to study its impact on the auditory phenotype. Compared to wild‐type (WT) control, transgenic Prps1 KI mice started to exhibit HL at 32 kHz at 4–12 weeks of age, with HL extending to 8 and 16 kHz by 48 weeks of age. A significant decrease in the number of hair cells and spiral ganglion neuron (SGN) counts was observed at 48 weeks of age in transgenic KI mice. These traits may be associated with the Bak‐dependent mitochondrial apoptosis program, which is triggered by oxidative stress and has been identified as a key mechanism of age‐related HL in C57BL/6J mice. Enzymatic assay showed a significant reduction in Prps1 enzymatic activity in KI compared to WT animals. The Prps1 p.Ala87Thr KI mouse model will serve as a valuable tool for developing therapeutic strategies to mitigate HL associated with PRPS1 variants.

Intercellular bridges (ICBs) are critical in intercellular communication, coordinated cellular development, and the equilibration of cytoplasmic contents between germ cells during vertebrate spermatogenesis. Mammalian TEX14 is specifically expressed in the testes and is a pivotal component of ICBs. It is indispensable for proper spermatogenesis; its deficiency causes meiotic arrest at the pachytene stage of meiotic prophase I, resulting in male infertility with non-obstructive azoospermia (NOA) in murine models. However, the specific effects of TEX14 deficiency on spermatogenesis remain poorly understood. In this study, we identified a novel compound heterozygous mutation in TEX14 (c.802A>T, p.S268C and c.1021C>T, p.R341*) in a patient with NOA. Functional analyses demonstrated that these mutations disrupted TEX14 synthesis. This led to spermatogenic failure characterized by meiotic arrest at the pachytene stage and impaired ICB assembly in the testes harboring the mutations. Our findings provide robust evidence that pathogenic biallelic TEX14 mutations are recurrent genetic etiologies of NOA in humans.

Childhood-onset dystonia, a clinically and genetically diverse group of disorders, can be challenging to diagnose. Information on the genotype and phenotype spectrum in the Indian population is limited. This study reports the clinical and molecular findings of monogenic childhood-onset dystonia in 22 individuals from 19 Indian families. Complex dystonia was the most frequent type, followed by combined and isolated forms. A total of 23 variants across 17 genes were identified, including nine novel ones. These disorders include four autosomal dominant, one X-linked recessive, one mitochondrial, and the remaining 11 autosomal recessive conditions. Five potentially treatable disorders were identified, and treatment was initiated in three families, showing satisfactory responses, particularly in dopa-responsive dystonias. Our study contributes four additional genes-CYP27A1, NDUFAF3, FUCA1, and FIG4-to the list of genes associated with complex dystonia. Exome sequencing proved crucial in diagnosing the etiology of dystonia, identifying treatable forms, and aiding genetic counseling. This study emphasizes the significance of using NGS for early genetic diagnosis to enable timely targeted therapies, offer precise genetic counseling to families, and prevent recurrence in the family.

Copy number variants (CNVs) contribute significantly to the pathogenicity of rare genetic diseases and tend to have a more severe effect on phenotype compared to single nucleotide variants (SNVs). In the past decades, exome sequencing (ES) has proven valuable input in the characterization of underlying genetic defects. Our aim was to investigate the impact of integrating CNV analysis tools into standard ES analysis on its diagnostic yield. We worked on ES data from an original cohort of 840 patients, in whom the first analysis was able to detect causative SNVs and indels in 383 (45.6%). Using the ExomeDepth algorithm, clinically relevant CNVs were identified in 55 patients out of the 457 unsolved cases, thus enhancing the diagnostic yield to 52.1%. Among the enrolled subjects, neurodevelopmental delay was the most prevalent phenotype. The detected CNVs comprised 43 deletions (74.1%) and 15 duplications (25.9%), ranging in size from 94 bp to 94.3 Mb, and were classified as 56 pathogenic/likely pathogenic and 2 uncertain with high interest. The study presents further evidence that incorporating CNV analysis tools into ES pipelines improves the diagnostic yield and emphasizes the involvement of CNVs in the etiology of genetic disorders.

The thoracic dystrophies are inherited skeletal conditions where abnormal embryonic development of the thoracic skeleton results in a narrow chest, pulmonary hypoplasia and respiratory insufficiency, which can be severe or lethal. The majority of thoracic dystrophies are due to biallelic alterations in genes needed for normal ciliary function. However, despite the identification of over 20 genes as causal for the thoracic dystrophy phenotype, around 20% of patients remain without a molecular diagnosis. We present two unrelated families with a clinical diagnosis of thoracic dystrophy with associated respiratory insufficiency without a molecular diagnosis on previous genetic testing. Both harbour rare biallelic and predicted deleterious missense substitutions in FGF4, a gene known to be essential for formation of the thoracic skeleton in mice. We demonstrate that the phenotype is restricted to short ribs, abnormally narrow chest and respiratory insufficiency, without other diagnostic clinical or radiological signs. We suggest that biallelic alterations in FGF4 are a newly identified disease association of thoracic dystrophy.

ABSTRACTNonsense‐mediated mRNA decay (NMD) plays a crucial role in degrading aberrant transcripts with premature termination codons, with the Up‐frameshift (UPF) protein family—UPF1, UPF2, and UPF3A/UPF3B—being vital components of this machinery. While several variants in genes encoding UPF2 and UPF3A/3B have been associated with neurodevelopmental disorders, only three germline UPF1 variants have been reported to date. Here, we report a male patient with a de novo missense variant, p.(Ala526Thr), in a highly conserved helicase motif of UPF1. The patient presented with moderate intellectual disability (ID), atypical autism, attention deficit hyperactivity disorder (ADHD), and behavioral disturbances. The common features observed among the four patients with UPF1 variants are moderate to severe ID and developmental delays in motor and verbal skills. A comparison across the disorders related to the UPF genes suggests that neurodevelopmental delay, including ID and impaired verbal skills, is a common feature, and these disorders may collectively be referred to as UPF‐related neurodevelopmental disorders (NDDs). ADHD, autism, seizures, hypotonia, and non‐specific dysmorphic features are also reported in some patients, suggesting that these disorders can be classified as non‐specific intellectual disability syndromes. However, further studies are necessary to elucidate genotype–phenotype correlations and the molecular mechanisms underlying these rare disorders, particularly those related to UPF1.

Mitochondria-associated paraplegin dysfunction is primarily linked to spastic paraplegia; however, genetic alterations in SPG7 have been associated with a broader spectrum of clinical symptoms. To identify disease-causing variants in the SPG7 gene, 437 patients with spastic ataxia, mitochondrial dysfunction-associated symptoms, or motoneuron lesions detected by EMG have been tested. We aimed to assess the clinical spectrum and determine the frequency of damaging variants within patient groups, particularly those less studied. Using ACMG criteria, we identified 10 pathogenic or likely pathogenic variants, 5 variants of uncertain significance with predicted damaging effects, and a probable risk factor variant in 58 patients. We identified 25 biallelic and 33 monoallelic cases. The most common variant was p. Leu78Ter (N = 23), followed by p. Ala510Val (N = 21). The point prevalence of SPG7-associated conditions in Hungary in 2024 is 0.46 per 100 000. In addition to well-characterized cohorts, SPG7 alterations were frequently identified in cohorts with multisystemic mitochondrial disease and lower motoneuron lesions. Multiple mtDNA deletions and histological abnormalities were consistently observed across all groups. In monoallelic cases, no evidence of a digenic effect involving AFG3L2 was found. Both autosomal dominant and recessive inheritance patterns were documented, with monoallelic cases typically presenting with a milder phenotype.

ABSTRACTLateralized overgrowth (LO) is characterized by excessive growth of one side of the body compared to the other. LO can present as isolated (ILO) or within syndromes, like Beckwith‐Wiedemann Spectrum (BWSp) and PIK3CA‐related overgrowth spectrum (PROS). Currently, the diagnosis of LO relies on clinical evaluation and lacks a standardized method. In this study, we evaluated total body dual‐energy X‐ray absorptiometry (TB‐DXA) as a potential tool for standardizing LO assessment. Patients with LO underwent both clinical evaluation and TB‐DXA. TB‐DXA data, including total mass, mass of the three main tissue components (adipose, muscle, and bone), total mass discrepancy ratio, relative tissue composition, and discrepancy of relative tissue composition were calculated and compared with clinical findings. Differences between affected regions and the contralateral side were assessed. A total of 46 patients (61% PROS, 24% BWSp, 15% ILO) were included in this study. TB‐DXA detected overgrowth regions aligned with clinical evaluation in 91% of cases and was able to identify localized overgrowth even when clinically overlooked. Additionally, TB‐DXA revealed differences in tissue composition between affected and unaffected regions for symmetrical body areas, with these differences varying by diagnostic subgroup. Different patterns of tissue composition overgrowth were observed among different conditions, with PROS predominantly showing adipose tissue overgrowth, while BWSp/ILO mainly osteo‐muscular overgrowth. TB‐DXA is an accurate, safe, and reproducible tool in the clinical setting providing an objective method for identifying and quantifying LO. It offers valuable guidance for clinicians in the diagnosis and management of LO.

Titin truncating variants (TTNtv) are the main genetic cause of dilated cardiomyopathies (DCMs). The phenotype and prognosis of probands have been evaluated in several large cohorts. However, few data are available on intrafamilial expressivity. To evaluate the phenotypical variability, we selected probands and family members carrying a unique TTN variant and recorded cardiac and genetic information. The cohort included 332 probands (314 TTNtv probands and 18 probands with in silico predicted in-frame exon skipping probands) and 191 relatives of TTNtv probands including 98 affected family members. Within TTNtv families, 96% of the affected relatives presented the same cardiomyopathy subtype as the proband, and 60% shared severity criteria (heart transplantation, implantable cardioverter-defibrillator, personal sudden death). Furthermore, we reported 18 probands that carry predicted in-frame exon skipping variants; they presented DCM (84%) as TTNtv patients but lower rate of rhythm disorders (0% vs. 29% respectively). In this work, we extend the genetic spectrum of TTNtv associated with DCM and show that within a family, and the cardiomyopathy phenotype is homogenous but the expressivity could vary. Such results are helpful for appropriate genetic counseling to better predict and manage the phenotype of mutation carriers.

An increasing number of autosomal recessive forms of adenomatous polyposis have been described, but some in very few cases. Here, we describe a rare case of biallelic germline pathogenic variants in the MLH3 gene, implicating it as a potential cause of early colorectal cancer. The patient, a 47-year-old woman, presented with rectal bleeding, leading to the discovery of a malignant rectal tumor and adenomas during colonoscopy. Histopathological examination confirmed adenocarcinoma without microsatellite instability, and genetic testing identified two likely pathogenic frameshift variants in MLH3 located in trans. These findings contribute to the expanding knowledge of MLH3-related polyposis and colorectal cancer and underscore the need for further research into the gene's broader implications, including its potential role in cancer and infertility pathways.