A Syndrome Affecting All Five Sense Organs: A Rare Congenital Disorder of Kabuki Makeup Syndrome With Multiple Pre-auricular Skin Tags.

Kabuki syndrome is an autosomal dominant disorder characterized by distinct facial features, including long palpebral fissures, a short columella with a flat, broad nasal tip, ptosis, and cleft lip/palate. The syndrome was named for the resemblance of the facial features to the make-up worn by traditional Kabuki performers. We report the case of a 10-month-old female infant admitted for cleft palate repair. The patient exhibited normal developmental milestones but had recurrent respiratory infections secondary to her cleft lip and palate. The child presented with significant facial dysmorphism, including long palpebral fissures with ptosis, multiple preauricular skin tags, a short columella with a depressed nasal tip, and microtia. These findings prompted differential diagnoses of Goldenhar syndrome, branchio-oculo-facial syndrome, and Kabuki syndrome. Whole exome sequencing confirmed a diagnosis of Kabuki syndrome. Given the autosomal dominant nature of this disorder, early identification and management of potential complications are crucial, as is parental counseling regarding the implications for future pregnancies.

WWOX-related epileptic encephalopathy caused by a novel mutation in the WWOX gene: a case report.

Background: WWOX-related epileptic encephalopathy is an autosomal recessive disorder caused by mutations in the WW-containing oxidoreductase gene, characterized by the onset of refractory seizures in infants. Early-onset epilepsy, electroencephalography abnormalities, and developmental delay or degeneration are the main clinical manifestations. Early death can occur in severe cases. In the present study, a novel variant in WWOX was detected in a patient with epilepsy and his healthy parents. Case presentation: A 5-month-old boy presented with epilepsy. The main manifestations were intractable seizures, mental and motor retardation and hearing impairment. Subsequent genetic testing revealed the presence of an epilepsy-associated novel mutation: c.991C>A (amino acid change: p.Ser304Tyr) in the WWOX gene. Variants were inherited from parents with healthy phenotypes. Finally, a patient died at 6 months of age. Conclusion: The discovery of novel variants has enriched the existing database of WWOX gene variants and may expand the range of clinical options for treating WWOX-related disorders.

Novel Genes of the Male Reproductive System: Potential Roles in Male Reproduction and as Non-hormonal Male Contraceptive Targets.

The development of novel non-hormonal male contraceptives represents a pivotal frontier in reproductive health, driven by the need for safe, effective, and reversible contraceptive methods. This comprehensive review explores the genetic underpinnings of male fertility, emphasizing the crucial roles of specific genes and structural variants (SVs) identified through advanced sequencing technologies such as long-read sequencing (LRS). LRS has revolutionized the detection of structural variants and complex genomic regions, offering unprecedented precision and resolution over traditional next-generation sequencing (NGS). Key genetic targets, including those implicated in spermatogenesis and sperm motility, are highlighted, showcasing their potential as non-hormonal contraceptive targets. The review delves into the systematic identification and validation of male reproductive tract-specific genes, utilizing advanced transcriptomics and genomics studies with validation using novel knockout mouse models. We discuss the innovative application of small molecule inhibitors, developed through platforms like DNA-encoded chemistry technology (DEC-Tec), which have shown significant promise in preclinical models. Notable examples include inhibitors targeting serine/threonine kinase 33 (STK33), soluble adenylyl cyclase (sAC), cyclin-dependent kinase 2 (CDK2), and bromodomain testis associated (BRDT), each demonstrating nanomolar affinity and potential for reversible and specific inhibition of male fertility. This review also honors the contributions of Dr. David L. Garbers whose foundational work has paved the way for these advancements. The integration of genomic, proteomic, and chemical biology approaches, supported by interdisciplinary collaboration, is poised to transform male contraceptive development. Future perspectives emphasize the need for continued innovation and rigorous testing to bring these novel contraceptives from the laboratory to clinical application, promising a new era of male reproductive health management.

Proof of Concept for Genome Profiling of the Neurofibroma/Sarcoma Sequence in Neurofibromatosis Type 1.

Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic disorder characterized by the predisposition to develop tumors such as malignant peripheral nerve sheath tumors (MPNSTs) which represents the primary cause of death for NF1-affected patients. Regardless of the high incidence and mortality, the molecular mechanisms underneath MPNST growth and metastatic progression remain poorly understood. In this proof-of-concept study, we performed somatic whole-exome sequencing (WES) to profile the genomic alterations in four samples from a patient with NF1-associated MPNST, consisting of a benign plexiform neurofibroma, a primary MPNST, and metastases from lung and skin tissues. By comparing genomic patterns, we identified a high level of variability across samples with distinctive genetic changes which allow for the definition of profiles of the early phase with respect to the late metastatic stages. Pathogenic and likely pathogenic variants were abundant in the primary tumor, whereas the metastatic samples exhibited a high level of copy-number variations (CNVs), highlighting a possible genomic instability in the late phases. The most known MPNST-related genes, such as TP53 and SUZ12, were identified in CNVs observed within the primary tumor. Pathway analysis of altered early genes in MPNST pointed to a potential role in cell motility, division and metabolism. Moreover, we employed survival analysis with the TCGA sarcoma genomic dataset on 262 affected patients, in order to corroborate the predictive significance of the identified early and metastatic MPNST driver genes. Specifically, the expression changes related to the mutated genes, such as in RBMX, PNPLA6 and AGAP2, were associated with reduced patient survival, distinguishing them as potential prognostic biomarkers. This study underlines the relevance of integrating genomic results with clinical information for early diagnosis and prognostic understanding of tumor aggressiveness.

Identification of a novel FGF3 variant and a new phenotype in three LAMM syndrome families.

Over 700 syndromes associated with hearing loss (HL) have been identified. Labyrinthine aplasia, microtia, and microdontia (LAMM syndrome, OMIM: 610706) is a rare HL syndrome characterized by congenital sensorineural HL, labyrinthine aplasia, type I microtia and microdontia, which is caused by biallelic variants in the FGF3 gene. Using Whole-exome sequencing (WES), we identified a novel missense FGF3 variant (c.137G > C, p. Arg46Pro (NM_005247.4) in three unrelated Uyghur ethnic families. This variant is classified as a variant of uncertain significance according to ACMG guidelines, with the applied criteria of PM3, PM2_Supporting, PP3 and PP4. Patients from the three families revealed variable clinical features. We found a novel phenotype, sparse hair, in one of the proband. Our findings expanded the variant and phenotype spectrum of LAMM syndrome and provided new insights to the diagnose and pathogenesis investigation of the disease.

Molecular diagnosis of patients with syndromic short stature identified by trio whole-exome sequencing.

Background: Short stature is a complex disorder with phenotypic and genetic heterogeneity. This study aimed to investigate clinical phenotypes and molecular basis of a cohort of patients with short stature. Methods: Trio whole-exome sequencing (Trio-WES) was performed to explore the genetic aetiology and obtain a molecular diagnosis in twenty Chinese probands with syndromic and isolated short stature. Results: Of the twenty probands, six (6/20, 30%) patients with syndromic short stature obtained a molecular diagnosis. One novel COMP pathogenic variant c.1359delC, p.N453fs*62 and one LZTR1 likely pathogenic variant c.509G>A, p.R170Q were identified in a patient with short stature and skeletal dysplasia. One novel de novo NAA15 pathogenic variant c.63T>G, p.Y21X and one novel de novo KMT2A pathogenic variant c.3516T>A, p.N1172K was identified in two probands with short stature, intellectual disability and abnormal behaviours, respectively. One patient with short stature, cataract, and muscle weakness had a de novo POLG pathogenic variant c.2863 T>C, p.Y955H. One PHEX pathogenic variant c.1104G>A, p.W368X was identified in a patient with short stature and rickets. Maternal uniparental disomy 7 (mUPD7) was pathogenic in a patient with pre and postnatal growth retardation, wide forehead, triangular face, micrognathia and clinodactyly. Thirteen patients with isolated short stature had negative results. Conclusion: Trio-WES is an important strategy for identifying genetic variants and UPD in patients with syndromic short stature, in which dual genetic variants are existent in some individuals. It is important to differentiate between syndromic and isolated short stature. Genetic testing has a high yield for syndromic patients but low for isolated patients.

Germline DNA Damage Repair Gene Alterations in Patients with Metachronous Breast and Colorectal Cancer.

A hereditary component of breast (BC) and colorectal cancer (CRC) has been described in approximately one-third of these tumor types. BC patients have an increased risk of developing CRC as a second primary tumor and vice versa. Germline genomic variants (NextSeq550, Illumina) were investigated in 24 unrelated BC and/or CRC patients and 7 relatives from 3 index patients. Fifty-six pathogenic or likely pathogenic variants were identified in 19 of 24 patients. We detected single-nucleotide variants (SNVs) in CRC predisposition genes (MLH1 and MUTYH) and other promising candidates (CDK5RAP3, MAD1L1, NOS3, and POLM). Eighteen patients presented SNVs or copy number variants (CNVs) in DNA damage repair genes. We also identified SNVs recently associated with BC or CRC predisposition (PABPC1, TYRO3, MAP3K1, SLC15A4, and LAMA1). The PABPC1c.1255C>T variant was detected in nine unrelated patients. Each patient presented at least one SNV/CNV in a candidate gene, and most had alterations in more than one gene, reinforcing a polygenic model for BC/CRC predisposition. A significant fraction of BC/CRC patients with a family history of these tumors harbored deleterious germline variants in DNA repair genes. Our findings can lead to strategies to improve the diagnosis, genetic counseling, and treatment of patients and their relatives.

Assessing pathogenicity of mismatch repair variants of uncertain significance by molecular tumor analysis.

Functional analyses are the main method to classify mismatch repair (MMR) gene variants of uncertain significance (VUSs). However, the pathogenicity remains unclear for many variants because of conflicting results between clinical, molecular, and functional data. In this study, we evaluated whether whole exome sequencing (WES) could add another layer of evidence to elucidate the pathogenicity of MMR variants with conflicting interpretations. WES was performed on formalin-fixed paraffin-embedded tumor tissue of eight patients with a constitutional MMR VUS (seven families), including eight colorectal and two endometrial carcinomas and one ovarian carcinoma. Cell-free CIMRA assays were performed to assign Odds of Pathogenicity to these VUSs. In four families, seven tumors showed MMR deficiency-associated mutational signatures, supporting the pathogenicity of the VUS. Moreover, somatic (second) MMR hits identified in the WES data were found to explain MMR staining patterns when the MMR staining was discordant with the reported germline MMR gene variant. In conclusion, WES did not significantly reclassify VUS in these cases but clarified some phenotypic aspects such as age of onset and explanations in case of discordant MMR stainings.

DOCK8 deficiency due to a deep intronic variant in two kindreds with hyper-IgE syndrome.

Dedicator of cytokinesis 8 (DOCK8) deficiency underlies the majority of cases of patients with autosomal recessive form of the hyper-immunoglobulin E syndrome (HIES). Most DOCK8 mutations involve deletions and splice junction mutations that abrogate protein expression. However, a few patients whose presentation is reminiscent of DOCK8 deficiency have no identifiable mutations. Using Whole Exome Sequencing (WES), we identified a deep intronic homozygous DOCK8 variant located in intron 36 (c.4626 + 76 A > G) in two unrelated patients with features of HIES that resulted in an in-frame 75 base pair intronic sequence insertion in DOCK8 cDNA, resulting in a premature stop codon (p.S1542ins6Ter). This variant resulted in variable decrease in DOCK8 expression that was associated with impaired T cell receptor-triggered actin polymerization, decreased IL-6-induced STAT3 phosphorylation, reduced expression of the Th17 cell markers CCR6 and IL-17, and higher frequencies of GATA3+ T cells indicative of Th2 skewing. Our approach extends the reach of WES in identifying disease-related intronic variants. It highlights the role of non-coding mutations in immunodeficiency disorders, including DOCK8 deficiency, and emphasizes the need to explore these mutations in unexplained inborn errors of immunity.

Whole­exome sequencing insights into synchronous bilateral breast cancer with discordant molecular subtypes.

The incidence of synchronous bilateral breast cancer (SBBC) is very low, and SBBC with discordant molecular subtypes is even more uncommon. As such, little is known about the pathogenesis of SBBC with discordant molecular subtypes, and reports about this entity are scarce. In the present study, the case of a 72-year-old female patient who presented with SBBC with discordant molecular subtypes is reported, with a stage IA hormone receptor negative {human epidermal growth factor receptor-2 [HER2(+)]} tumor in the left breast and a stage IIIA hormone sensitive tumor [HER2(-)] in the right breast. Whole-exome sequencing was performed to identify the differential genetic variations in the BBC tissues. A total of 8 key mutated cancer susceptibility genes (ALK, BRCA1, FAT1, HNF1A, KDR, PTCH1, SDHA and SETBP1) were screened, and mutations were found in 10 vital cancer driver genes, including BRCA1, EBF1, MET, NF2, NUMA1 RALGAPA1, ROBO2, SMYD4, UBR5 and ZNF844. The high-frequency mutated genes mainly contained missense mutations, among which single nucleotide variants were the most common mutations, with C > T and C > A as the main forms. The pathways associated with the high frequency mutated genes were further elucidated by functional category and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses. Heterogeneity in the hormone receptor and HER2 status of SBBC poses unique therapeutic challenges. Future studies should aim to identify the optimal management strategy for this disease.

Identification of novel variants in hereditary spherocytosis patients by whole-exome sequencing.

Defects in erythrocyte membrane proteins can cause the most common type of inherited hemolytic anemia, so called hereditary spherocytosis (HS). It is characterized by the appearance of spherocytes in peripheral blood, hemolytic anemia, splenomegaly, jaundice and gallstones. Due to difficulty of diagnosis solely based on aforementioned parameters, the addition of genetic testing seems to be effective and most acknowledged. Up to date, pathogenic variations in five genes encoding membrane proteins (ANK1, SPTA1, SPTB, SLC4A1, EPB42) are identified to cause HS. Here, we have studied the genetic spectrum in forty-one patients with clinically suspected HS and their families, as well as their genotype-phenotype correlations. Pathogenic mutations in ANK1, SPTB, SLC4A1 and SPTA1 were found in 17 (41.5 %), 12 (29.3 %), 7 (17.1 %) and 5 (12.2 %) patients, respectively. Deleterious variants include 12 missense, 15 nonsense, 12 frameshift, and 4 splicing variants. Among these variations 32 were novel. In our genotype-phenotype analysis, platelet levels in SPTB (p = 0.021) and SLC4A1 (p = 0.02) patients were found to be significantly lower than ANK1 patients. In addition, LDH levels in SPTB patients were remarkably lower than patients with ANK1 mutations (p = 0.025).

Assessment of cancer predisposition syndromes in children with leukemia and solid tumors: germline-genomic profiling and clinical features in a series of cases.

Cancer predisposition syndromes (CPS) are a group of genetic disorders that increase the risk of various cancers. Identifying CPS has a significant impact on the treatment plan, screening and follow-up strategy, and genetic counseling of the family. However, in children, it goes underdiagnosed in most clinical setups, especially in low- and middle-income (LMIC) countries. In the present study, we screened 60 pediatric oncology patients for a possible CPS based on pre-defined selection criteria. Six patients met the criteria, three of whom had hematological malignancy, while the remaining three had sarcoma. Whole exome sequencing was performed in the selected patients to confirm the diagnosis. Germline mutation in CPS-related genes was discovered in five of six cases, including novel mutations discovered in two. An adverse outcome was observed in all five patients with underlying cancer predisposition syndrome, with three having relapsed and two having progressive disease. Our study reflects a prevalence of 10% underlying CPS in a limited cohort of patient based on the phenotype-genotype approach in our cohort. Using pre-defined clinical selection criteria, screening can be directed to a high-risk patient cohort with high-pick up rate for CPS. The selection criteria could be utilized in any LMIC-based clinical setup for pediatric cancer patients who may benefit from modification of treatment as well as genetic counseling.

Phase II trial of imatinib mesylate in patients with PDGFRA/B-negative hypereosinophilic syndrome.

The role of imatinib in PDGFRA/B-negative hypereosinophilic syndromes (HES) is controversial because of the heterogeneity of HES and the scarcity of prospective studies. We conducted a phase II clinical trial to evaluate the efficacy of imatinib in PDGFRA/B-negative HES. Thirty-two patients were treated with imatinib (100-400 mg daily), and the molecular basis of their response was identified using whole-exome sequencing (WES) and whole-transcriptome sequencing (WTS). The haematological response rate was 46.9%, with a complete haematological response (CHR) rate of 18.8%. The median time to response was 1.5 months. Among the six patients who achieved CHR, five maintained it until the 24th cycle of imatinib and one lost response after 20 months. The median progression-free survival was 4.3 months. WES and WTS were conducted for 11 patients. The number of non-silent mutations did not differ between responders and non-responders. Nine differentially expressed genes, including SNORD15A, were downregulated in responders. STAT5B::RARA, PAK2::PIGX, and FIP1L1::CHIC2 fusions were identified in patients with sustained responses, and RNF130::BRAF and WNK1::KDM5A fusions were identified in non-responders. Imatinib, along with an appropriate biomarker, could be a promising option for PDGFRA/B-negative HES.

Non-syndromic perspective on a unique progressive familial intrahepatic cholestasis variant: ZFYVE19 mutation.

BACKGROUND: ZFYVE19 mutation has been recently identified as one of the non-syndromic causes of cholestasis. It is associated with elevated gamma-glutamyl transferase levels and is likely a cause of neonatal-onset and intrahepatic cholestasis. CASE: Here, we report a rare case of ZFYVE19 defect, confirmed by whole exome sequencing (WES). Our patient, who is currently 4 years old, presented to us at the age of 2 years with elevated levels of serum transaminases and bilirubin. WES revealed a homozygous ZFYVE19 mutation despite preserved synthetic liver function. This gene has recently been identified in the literature as a cause of non-classical progressive familial intrahepatic cholestasis (OMIM # 619849). Treatment with an appropriate dose of ursodeoxycholic acid resulted in the regression of elevated liver enzymes and itching. The patient's body mass index progressively increased throughout the treatment period. No medication side effects were observed at any point. Currently, the patient remains asymptomatic during follow-up. CONCLUSION: We have identified the ZFYVE19 mutation as a variant that is not accompanied by any other symptoms. However, we have limited knowledge about the progression of the disease and are closely monitoring the patient for potential liver-related issues. Using WES in cases of undiagnosed liver enzyme elevations or cholestasis can help identify new genes and improve our understanding of the underlying pathophysiology.

Identification of a Novel Frameshift variant of the ATRX gene: a Case Report and Review of the genotype-phenotype relationship.

BACKGROUND: X-linked intellectual disability-hypotonic facies syndrome-1 (MRXHF1) and Alpha-thalassemia X-linked intellectual disability (ATR-X) syndrome are caused by pathogenic variant in the ATRX gene, a member of the switch/sucrose non-fermentable (SWI-SNF) protein family that exhibits chromatin remodeling activity. These syndromes show a wide spectrum of clinical manifestations, such as distinctive dysmorphic features, mild-to-profound intellectual disability, motor development delay, seizures, urogenital abnormalities, and gastrointestinal disorders. CASE PRESENTATION AND LITERATURE REVIEW: A 3-year-old boy from a Chinese non-consanguineous family was diagnosed with MRXHF1 by whole-exome sequencing. Comprehensive family history information was obtained. The Medline database was searched until 1st Aug 2023 for articles related to ATRX pathogenic variant. Data on gene/protein mutations and clinical symptoms were extracted. The proband showed intellectual disability, motor development delay, typical facial abnormalities, urogenital defect, behavior problems, and optical nerve dysplasia. A novel frameshift mutation c.399_400dup, (p.Leu134Cysfs*2) in the ATRX gene was the primary cause, which occurs right before the ATRXDNMT3-DNMT3L (ADD) domain of ATRX protein. Missense mutation is the most common variation type. The ADD and helicase-like domains are the most frequently affected domains. Epilepsy, congenital heart disease, urogenital defect, acoustic defect, and optical defect are more prevalent in patients with frameshift mutations compared to those with missense mutations. There are more urogenital defects with C-terminal frameshift mutations than with N-terminal frameshift mutations. CONCLUSION: We described a novel frameshift mutation in the ATRX gene in a patient with MRXHF1 syndrome and summarized the genotype-phenotype relationship of ATRX pathogenic variant by variation type and affected protein domain. The regulatory mechanism underlying ATRX variant requires comprehensive analysis in future studies.

Whole Exome Sequencing in Children With Type 1 Diabetes Before Age 6 Years Reveals Insights Into Disease Heterogeneity.

Aims: This study is aimed at comparing whole exome sequencing (WES) data with the clinical presentation in children with type 1 diabetes onset ≤ 5 years of age (EOT1D). Methods: WES was performed in 99 unrelated children with EOT1D with subsequent analysis to identify potentially deleterious rare variants in MODY genes. High-resolution HLA class II haplotyping, SNP genotyping, and T1D-genetic risk score (T1D-GRS) were also evaluated. Results: Eight of the ninety-nine EOT1D participants carried a potentially deleterious rare variant in a MODY gene. Rare variants affected five genes: GCK (n = 1), HNF1B (n = 2), HNF4A (n = 1), PDX1 (n = 2), and RFX6 (n = 2). At diagnosis, these children had a mean age of 3.0 years, a mean HbA1c of 10.5%, a detectable C-peptide in 5/8, and a positive islet autoantibody in 6/7. Children with MODY variants tend to exhibit a lower number of pancreatic autoantibodies and a lower fasting C-peptide compared to EOT1D without MODY rare variants. They also carried at least one high-risk DR3-DQ2 or DR4-DQ8 haplotype and exhibited a T1D-GRS similar to the other individuals in the EOT1D cohort, but higher than healthy controls. Conclusions: WES found potentially deleterious rare variants in MODY genes in 8.1% of EOT1D, occurring in the context of a T1D genetic background. Such genetic variants may contribute to disease precipitation by a ß-cell dysfunction mechanism. This supports the concept of different endotypes of T1D, and WES at T1D onset may be a prerequisite for the implementation of precision therapies in children with autoimmune diabetes.

Preliminary identification of somatic mutations profile in ACL injury.

Anterior cruciate ligament (ACL) injury is a common orthopedic disease with a high incidence, long recovery time, and often requiring surgical treatment. However, the susceptibility factors for ACL injury are currently unclear, and there is a lack of analysis on the differences in the ligament itself. Previous studies have focused on germline mutations, with less research on somatic mutations. To determine the role of somatic mutations in ACL injuries, we recruited seven patients between the ages of 20 and 39 years diagnosed with ACL injuries, collected their peripheral blood, injured ligament ends, and healthy ligament ends tissues, and performed exome sequencing with gene function enrichment analysis. We detected multiple gene mutations and gene deletions, which were only present in some of the samples. Unfortunately, it was not possible to determine whether these somatic mutations are related to ligament structure or function, or are involved in ACL injury. However, this study provides valuable clues for future in-depth research.

A novel RPE65 variant p.(Ala391Asp) in Leber congenital amaurosis: a case report and literature review in Japan.

Introduction: In Japan, inherited retinal dystrophy caused by biallelic variants of the RPE65 gene is exceedingly rare. The purpose of this study was to describe a Japanese male patient with a novel variant in RPE65 associated with Leber congenital amaurosis (LCA). Case report: The patient, diagnosed with LCA, exhibited infantile nystagmus and reported experiencing night blindness since early childhood. At 27 years of age, the patient underwent an ophthalmologically evaluation. Corrected visual acuity was Snellen equivalent 20/133 in the right eye and Snellen equivalent 20/100 in the left eye. Fundus examination revealed alterations in the retinal pigment epithelium characterized by hypopigmentation and narrowing of retinal vessels. Fundus autofluorescence imaging demonstrated a generally diminished autofluorescent signal. Full-field electroretinography identified a generalized dysfunction of both rod and cone systems in each eye. Whole exome sequencing identified a novel missense variant in RPE65 (NM_000329.3): c.1172C > A p.(Ala391Asp), which was classified as pathogenic, as well as a recurrent variant p.(Arg515Trp). Conclusion: This study provides valuable insights into the genotype-phenotype correlation of RPE65-associated LCA in Japanese patients, with critical implications for enhanced diagnostic accuracy and informed therapeutic decisions.

Biallelic Deletion of PEX26 Exon 4 in a Boy with Phenotypic Features of both Zellweger Syndrome and Infantile Refsum Disease.

Introduction: Peroxisome biogenesis disorders (PBDs) encompass a group of diseases marked by clinical and genetic heterogeneity. Phenotypes linked to PBDs include Zellweger syndrome, neonatal adrenoleukodystrophy, infantile Refsum disease (IRD), rhizomelic chondrodysplasia punctata type 1, and Heimler syndrome. PBD phenotypes manifest through hypotonia, developmental delay, facial dysmorphism, seizures, liver dysfunction, sensorineural hearing loss, and retinal dystrophy. Methods: The proband underwent comprehensive clinical evaluation, followed by whole-exome sequencing (WES) coupled with copy number analysis (CNV), aimed at identifying potential disease-causing variants aligning with the observed phenotype. Results: Our findings detail an individual exhibiting developmental delay, hearing loss, visual impairment, hepatomegaly, and splenomegaly, attributed to a biallelic deletion of exon 4 in the PEX26 gene. The WES analysis of the index case did not uncover any pathogenic/likely pathogenic single-nucleotide variations that could account for the observed clinical findings. However, the CNV data derived from WES revealed a homozygous deletion in exon 4 of the PEX26 gene (NM_001127649.3), providing a plausible explanation for the patient's clinical features. The exon 4 region of PEX26 encodes the transmembrane domain of the protein. The transmembrane domain plays a crucial role in anchoring the protein within lipid bilayers, and its absence can disrupt proper localization and functioning. As a result, this structural alteration may impact the protein's ability to facilitate essential cellular processes related to peroxisome biogenesis and function. Conclusion: The index patient, which presented with hearing loss, retinal involvement and hepatic dysfunction in adolescence age, has atypical clinical course that can be considered unusual for Zellweger syndrome (ZS) and IRD phenotypes, and its rare genotypic data (in-frame single exon deletion) expands the PBD disease spectrum. This study revealed for the first time that PEX26 protein transmembrane domain loss exhibits an unusual course with clinical findings of IRD and ZS phenotypes. WES studies, incorporating CNV analyses, empower the identification of novel genetic alterations in genes seldom associated with gross deletion/duplication variations, such as those in the PEX26 gene. This not only enhances diagnostic rates in rare diseases but also contributes to broadening the spectrum of causal mutations.