Genetic landscape of congenital insensitivity to pain and hereditary sensory and autonomic neuropathies.

Congenital insensitivity to pain (CIP) and hereditary sensory and autonomic neuropathies (HSAN) are clinically and genetically heterogeneous disorders exclusively or predominantly affecting the sensory and autonomic neurons. Due to the rarity of the diseases and findings based mainly on single case reports or small case series, knowledge about these disorders is limited. Here, we describe the molecular workup of a large international cohort of CIP/HSAN patients including patients from normally under-represented countries. We identify 80 previously unreported pathogenic or likely pathogenic variants in a total of 73 families in the >20 known CIP/HSAN-associated genes. The data expand the spectrum of disease-relevant alterations in CIP/HSAN, including novel variants in previously rarely recognized entities such as ATL3-, FLVCR1- and NGF-associated neuropathies and previously under-recognized mutation types such as larger deletions. In silico predictions, heterologous expression studies, segregation analyses and metabolic tests helped to overcome limitations of current variant classification schemes that often fail to categorize a variant as disease-related or benign. The study sheds light on the genetic causes and disease-relevant changes within individual genes in CIP/HSAN. This is becoming increasingly important with emerging clinical trials investigating subtype or gene-specific treatment strategies.

A tapt1 knock-out zebrafish line with aberrant lens development and impaired vision models human early-onset cataract.

Bi-allelic mutations in the gene coding for human trans-membrane anterior-posterior transformation protein 1 (TAPT1) result in a broad phenotypic spectrum, ranging from syndromic disease with severe skeletal and congenital abnormalities to isolated early-onset cataract. We present here the first patient with a frameshift mutation in the TAPT1 gene, resulting in both bilateral early-onset cataract and skeletal abnormalities, in addition to several dysmorphic features, in this way further expanding the phenotypic spectrum associated with TAPT1 mutations. A tapt1a/tapt1b double knock-out (KO) zebrafish model generated by CRISPR/Cas9 gene editing revealed an early larval phenotype with eye malformations, loss of vision, increased photokinetics and hyperpigmentation, without visible skeletal involvement. Ultrastructural analysis of the eyes showed a smaller condensed lens, loss of integrity of the lens capsule with formation of a secondary lens and hyperplasia of the cells in the ganglion and inner plexiform layers of the retina. Transcriptomic analysis pointed to an impaired lens development with aberrant expression of many of the crystallin and other lens-specific genes. Furthermore, the phototransduction and visual perception pathways were found to be significantly disturbed. Differences in light perception are likely the cause of the increased dark photokinetics and generalized hyperpigmentation observed in this zebrafish model. In conclusion, this study validates TAPT1 as a new gene for early-onset cataract and sheds light on its ultrastructural and molecular characteristics.

Novel pathogenic variants in NLRP7, NLRP5, and PADI6 in patients with recurrent hydatidiform moles and reproductive failure.

Recurrent hydatidiform moles (RHMs) are human pregnancies with abnormal embryonic development and hyperproliferating trophoblast. Biallelic mutations in NLRP7 and KHDC3L, members of the subcortical maternal complex (SCMC), explain the etiology of RHMs in only 60% of patients. Here we report the identification of seven functional variants in a recessive state in three SCMC members, five in NLRP7, one in NLRP5, and one in PADI6. In NLRP5, we report the first patient with RHMs and biallelic mutations. In PADI6, the patient had four molar pregnancies, two of which had fetuses with various abnormalities including placental mesenchymal dysplasia and intra-uterine growth restriction, which are features of Beckwith-Wiedemann syndrome and Silver Russell syndrome, respectively. Our findings corroborate recent studies and highlight the common oocyte origin of all these conditions and the continuous spectrum of abnormalities associated with deficiencies in the SCMC genes.

Excess of de novo variants in genes involved in chromatin remodelling in patients with marfanoid habitus and intellectual disability.

PURPOSE: Marfanoid habitus (MH) combined with intellectual disability (ID) (MHID) is a clinically and genetically heterogeneous presentation. The combination of array CGH and targeted sequencing of genes responsible for Marfan or Lujan-Fryns syndrome explain no more than 20% of subjects. METHODS: To further decipher the genetic basis of MHID, we performed exome sequencing on a combination of trio-based (33 subjects) or single probands (31 subjects), of which 61 were sporadic. RESULTS: We identified eight genes with de novo variants (DNVs) in at least two unrelated individuals (ARID1B, ATP1A1, DLG4, EHMT1, NFIX, NSD1, NUP205 and ZEB2). Using simulation models, we showed that five genes (DLG4, NFIX, EHMT1, ZEB2 and ATP1A1) met conservative Bonferroni genomewide significance for an excess of the observed de novo point variants. Overall, at least one pathogenic or likely pathogenic variant was identified in 54.7% of subjects (35/64). These variants fell within 27 genes previously associated with Mendelian disorders, including NSD1 and NFIX, which are known to be mutated in overgrowth syndromes. CONCLUSION: We demonstrated that DNVs were enriched in chromatin remodelling (p=2×10-4) and genes regulated by the fragile X mental retardation protein (p=3×10-8), highlighting overlapping genetic mechanisms between MHID and related neurodevelopmental disorders.

Bain type of X-linked syndromic mental retardation in a male with a pathogenic variant in HNRNPH2.

Heterogeneous nuclear ribonucleoproteins (hnRNPs) are RNA binding proteins, which aid in maturation, stabilization, and transport of mRNA. They have a significant role in cellular nucleic acid metabolism. The hnRNPs alter gene expression and are linked to various neurodegenerative disorders and cancers. Previously, six unrelated girls with developmental delay, intellectual disability, and hypotonia were found to have de novo heterozygous pathogenic missense variants in HNRNPH2, located on the X chromosome. A gain-of-function effect was proposed for the variant and it was thought to be lethal in males as no surviving males were identified. We describe a family with two affected siblings, one male and one female, with a known pathogenic variant in HNRNPH2, possibly due to maternal germline mosaicism.

Locus and allelic heterogeneity and phenotypic variability in Waardenburg syndrome.

Waardenburg syndrome (WS) is a disorder of neural crest cell migration characterized by auditory and pigmentary abnormalities. We investigated a cohort of 14 families (16 subjects) either by targeted sequencing or whole-exome sequencing. Thirteen of these families were clinically diagnosed with WS and one family with isolated non-syndromic hearing loss (NSHL). Intra-familial phenotypic variability and non-penetrance were observed in families diagnosed with WS1, WS2 and WS4 with pathogenic variants in PAX3, MITF and EDNRB, respectively. We observed gonosomal mosaicism for a variant in PAX3 in an asymptomatic father of two affected siblings. For the first time, we report a biallelic pathogenic variant in MITF in a subject with WS2 and a biallelic variant in EDNRB was noted in a subject with WS2. An individual with isolated NSHL carried a pathogenic variant in MITF. Blended phenotype of NSHL and albinism was observed in a subject clinically diagnosed to have WS2. A phenocopy of WS1 was observed in a subject with a reported pathogenic variant in GJB2, known to cause isolated NSHL. These novel and infrequently reported observations exemplify the allelic and genetic heterogeneity and show phenotypic diversity of WS.

Ptosis as a unique hallmark for autosomal recessive WNT1-associated osteogenesis imperfecta.

Osteogenesis imperfecta (OI) is a heritable connective tissue disorder, mainly characterized by bone fragility and low bone mass. Defects in the type I procollagen-encoding genes account for the majority of OI, but increasingly more rare autosomal recessive (AR) forms are being identified, which are caused by defects in genes involved in collagen metabolism, bone mineralization, or osteoblast differentiation. Bi-allelic mutations in WNT1 have been associated with a rare form of AR OI, characterized by severe osteoporosis, vertebral compression, scoliosis, fractures, short stature, and variable neurological problems. Heterozygous WNT1 mutations have been linked to autosomal dominant early-onset osteoporosis. In this study, we describe the clinical and molecular findings in 10 new patients with AR WNT1-related OI. Thorough revision of the clinical symptoms of these 10 novel patients and previously published AR WNT1 OI cases highlight ptosis as a unique hallmark in the diagnosis of this OI subtype.

Utility and performance of bacterial artificial chromosomes-on-beads assays in chromosome analysis of clinical prenatal samples, products of conception and blood samples.

AIM: Chromosome analysis of prenatal samples and products of conception (POC) has conventionally been done by karyotyping (KT). Shortcomings of KT like high turnaround time and culture failure led to technology innovations, such as the bacterial artificial chromosomes (BAC)s-on-Beads (BoBs)-based tests, Prenatal BoBs (prenatal samples) and KaryoLite BoBs (POC samples). In the present study, we validated and evaluated the utility of each test on prenatal, POC and blood samples. METHODS: Study A (n = 305; 259 prenatal + 46 blood/POC) and Study B (n = 176; 146 POC/chorionic vill + 30 blood/amniotic fluid) samples were analyzed using Prenatal and KaryoLite BoBs kits, respectively. KT, array-based Comparative Genomic Hybridization (arrayCGH) and fluorescence in situ hybridization (FISH) were used for comparison of results. Ability of KaryoLite BoBs to identify ring chromosomes was tested. RESULTS: Prenatal BoBs had zero test failure rate and results of all samples were concordant with KT results. Totally four microdeletions were identified by Prenatal BoBs but not by KT. In Study B, all but two POC samples (one triploid and one tetraploid) were concordant with KT and arrayCGH. Partial chromosomal imbalance detection rate was ~64% and KaryoLite BoBs indicated the presence of a ring chromosome in all four cases. The failure rate of KaryoLite BoBs was 3%. CONCLUSION: We conclude that Prenatal BoBs (common aneuploidies and nine microdeletions) together with KT constitutes more comprehensive prenatal testing compared to FISH and KT. KaryoLite BoBs for aneuploidies of all chromosomes is highly successful in POC analysis and the ability to indicate presence of ring chromosomes improves its clinical sensitivity. Both tests are robust and could also be used for different specimens.

A Child Presenting with Recurrent Corneal Ulcers: Hereditary Sensory and Autonomic Neuropathy IV (HSAN IV).

Hereditary Sensory and Autonomic Neuropathy IV (HSAN IV) or Congenital Insensitivity to pain and Anhidrosis is an autosomal recessive condition. It is characterized by absence of reaction to painful stimuli, anhidrosis, self-mutilating behaviour and episodic fever. We report a child with HSAN IV who presented primarily with recurrent corneal ulcers and the classical history helped us clinch the diagnosis. Molecular testing revealed a homozygous pathogenic frameshift mutation in NTRK1 c.717delG, p.(Met239fs). Molecular testing is confirmatory and this will help the family in future prenatal diagnosis.

The genetics of recurrent hydatidiform moles: new insights and lessons from a comprehensive analysis of 113 patients.

Hydatidiform mole is an aberrant human pregnancy characterized by early embryonic arrest and excessive trophoblastic proliferation. Recurrent hydatidiform moles are defined by the occurrence of at least two hydatidiform moles in the same patient. Fifty to eighty percent of patients with recurrent hydatidiform moles have biallelic pathogenic variants in NLRP7 or KHDC3L. However, in the remaining patients, the genotypic types of the moles are unknown. We characterized 80 new hydatidiform mole tissues, 57 of which were from patients with no mutations in the known genes, and we reviewed the genotypes of a total of 123 molar tissues. We also reviewed mutation analysis in 113 patients with recurrent hydatidiform moles. While all hydatidiform moles from patients with biallelic NLRP7 or KHDC3L mutations are diploid biparental, we demonstrate that those from patients without mutations are highly heterogeneous and only a small minority of them are diploid biparental (8%). The other mechanisms that were found to recur in patients without mutations are diploid androgenetic monospermic (24%) and triploid dispermic (32%); the remaining hydatidiform moles were misdiagnosed as moles due to errors in the analyses and/or their unusual mechanisms. We compared three parameters of genetic susceptibility in patients with and without mutations and show that patients without mutations are mostly from non-familial cases, have fewer reproductive losses, and more live births. Our data demonstrate that patients with recurrent hydatidiform moles and no mutations in the known genes are, in general, different from those with mutations; they have a milder genetic susceptibility and/or a multifactorial etiology underlying their recurrent hydatidiform moles. Categorizing these patients according to the genotypic types of their recurrent hydatidiform moles may facilitate the identification of novel genes for this entity.

Mutations in CSPP1 cause primary cilia abnormalities and Joubert syndrome with or without Jeune asphyxiating thoracic dystrophy.

Joubert syndrome (JBTS) is a recessive ciliopathy in which a subset of affected individuals also have the skeletal dysplasia Jeune asphyxiating thoracic dystrophy (JATD). Here, we have identified biallelic truncating CSPP1 (centrosome and spindle pole associated protein 1) mutations in 19 JBTS-affected individuals, four of whom also have features of JATD. CSPP1 mutations explain ∼5% of JBTS in our cohort, and despite truncating mutations in all affected individuals, the range of phenotypic severity is broad. Morpholino knockdown of cspp1 in zebrafish caused phenotypes reported in other zebrafish models of JBTS (curved body shape, pronephric cysts, and cerebellar abnormalities) and reduced ciliary localization of Arl13b, further supporting loss of CSPP1 function as a cause of JBTS. Fibroblasts from affected individuals with CSPP1 mutations showed reduced numbers of primary cilia and/or short primary cilia, as well as reduced axonemal localization of ciliary proteins ARL13B and adenylyl cyclase III. In summary, CSPP1 mutations are a major cause of the Joubert-Jeune phenotype in humans; however, the mechanism by which these mutations lead to both JBTS and JATD remains unknown.

Additional three patients with Smith-McCort dysplasia due to novel RAB33B mutations.

Smith-McCort dysplasia (SMC OMIM 615222) and Dyggve-Melchior-Clausen dysplasia (DMC OMIM 223800) are allelic skeletal dysplasias caused by homozygous or compound heterozygous mutations in DYM (OMIM 607461). Both disorders share the same skeletal phenotypes characterized by spondylo-epi-metaphyseal dysplasia with distinctive lacy ilia. The difference rests on the presence or absence of intellectual disability, that is, intellectual disability in DMC and normal cognition in SMC. However, genetic heterogeneity was suspected in SMC. Recently, RAB33B (OMIM 605950) has been identified as the second gene for SMC. Nevertheless, only two affected families have been reported so far. Here we present three SMC patients with four novel pathogenic variants in RAB33B, including homozygosity for c.211C>T (p.R71*), homozygosity for c.365T>C (p.F122S), and compound heterozygosity for c.48delCGGGGCAG (p.G17Vfs*58) and c.490C>T (p.Q164*). We also summarize the clinical, radiological, and mutation profile of RAB33B after literature mining. This report ascertains the pathogenic relationship between RAB33B and SMC. © 2017 Wiley Periodicals, Inc.

Persistent Left Superior Vena Cava in Fetuses: An Autopsy Series.

OBJECTIVE: To review fetal autopsy reports with persistent left superior vena cava (PLSVC) and identify its associations. MATERIALS AND METHODS: Autopsy reports of all fetuses diagnosed with PLSVC in our center from January 2011 to December 2015 were reviewed. Fetuses less than 15 weeks gestational age along with autolyzed and damaged hearts were excluded from the study. The study group was compared with controls during this period. RESULTS: Prenatal ultrasound detection rate of PLSVC was 13.06%. All the cases had associated anomalies of which 96% had extra cardiac anomalies and 67% had intrinsic cardiac defects among which septal defects were most common (39.6%). Anomalies of cardiovascular, respiratory, genitourinary and musculoskeletal, hypoplastic thymus and single umbilical artery were significantly higher in the study group. CONCLUSION: This study emphasizes on the importance of improving the technical skill for imaging the three-vessel view as PLSVC seems to have significant associations.

Mutations in ECEL1 cause distal arthrogryposis type 5D.

Distal arthrogryposis (DA) syndromes are the most common of the heritable congenital-contracture disorders, and ~50% of cases are caused by mutations in genes that encode contractile proteins of skeletal myofibers. DA type 5D (DA5D) is a rare, autosomal-recessive DA previously defined by us and is characterized by congenital contractures of the hands and feet, along with distinctive facial features, including ptosis. We used linkage analysis and whole-genome sequencing of a multiplex consanguineous family to identify in endothelin-converting enzyme-like 1 (ECEL1) mutations that result in DA5D. Evaluation of a total of seven families affected by DA5D revealed in five families ECEL1 mutations that explain ~70% of cases overall. ECEL1 encodes a neuronal endopeptidase and is expressed in the brain and peripheral nerves. Mice deficient in Ecel1 exhibit perturbed terminal branching of motor neurons to the endplate of skeletal muscles, resulting in poor formation of the neuromuscular junction. Our results distinguish a second developmental pathway that causes congenital-contracture syndromes.

A homozygous stop codon in HORMAD2 in a patient with recurrent digynic triploid miscarriage.

BACKGROUND: Recurrent miscarriage (RM) affects 1% to 5% of couples trying to conceive. Despite extensive clinical and laboratory testing, half of the RM cases remain unexplained. We report the genetic analysis of a couple with eight miscarriages and the search for their potential genetic etiology. METHODS: Short tandem repeat (STR) markers, single nucleotide polymorphic (SNP) microarray, and human DNA methylation microarray were used to analyze the genotypes of two miscarriages. Exomes sequencing was performed on DNA from the two partners and identified variants were validated by Sanger sequencing. RESULTS: STR marker genotyping demonstrated that the two available miscarriages are triploid digynic and resulted from the failure of Meiosis II. SNP microarray analysis revealed an additional Meiosis I abnormality that is the segregation of the two maternal homologous chromosomes in one triploid miscarriage. Whole-exome sequencing on DNA from the two partners identified candidate variants only in the female partner in two genes with roles in female reproduction, a missense in EIF4ENIF1 (OMIM 607445) and a stop gain in HORMAD2 (OMIM 618842). EIF4ENIF1 is a eukaryotic translation initiation factor 4E nuclear import factor required for the oocyte germinal vesicle breakdown, and HORMAD2 is part of the synaptonemal complex that was hypothesized to act as a checkpoint mechanism to eliminate oocytes with asynapsis during meiotic prophase I in mice. CONCLUSION: While both genes may contribute to the phenotype, the Meiosis I abnormalities in the conceptions favor the causal role of HORMAD2 in the etiology of RM in this couple. This report illustrates the importance of comprehensively analyzing the products of conception to guide the search for the genetic causation of RM.

Biotinidase deficiency: an atypical presentation.

Biotinidase deficiency is a rare metabolic disorder which can cause dermatological manifestations and lead to severe neurological sequelae if untreated. Holocarboxylase synthetase deficiency also has similar manifestations and needs to be differentiated. We present a neonate who had atypical early onset symptoms and was diagnosed to have biotinidase deficiency.

Novel pathogenic variant c.2714C>A (p. Thr905Lys) in the HK1 gene causing severe haemolytic anaemia with developmental delay in an Indian family.

Hexokinase (EC 2.7.1.1, Adenosine Tri Phosphate (ATP): D-hexose-6-phosphotransferase) is a crucial regulatory enzyme of the glycolytic pathway (Embden-Meyerhof pathway). Hexokinase deficiency is associated with chronic non-spherocytic haemolytic anaemia (HA) with some exceptional cases showing psychomotor/mental retardation and fetus death. The proband is a four-and-half-year-old female child born of a four-degree consanguineous marriage hailing from South India with autosomal recessive congenital HA associated with developmental delay. She was well till 3 months of her age post an episode of diarrhoea when she was noted to be severely anaemic and requiring regular transfusions. The common causes of HA, haemoglobinopathies, red cell membranopathies and common red cell enzymopathies (G6PD, GPI, PK and P5N) were ruled out. Targeted analysis of whole exome sequencing (WES) using an insilico gene panel for hereditary anaemia was performed to identify pathogenic variants in the patient. Next-generation sequencing revealed a novel homozygous variant in hexokinase gene c.2714C>A (p. Thr905Lys) in exon-18. The pathogenic nature of the variant p. Thr905Lys in the HK1 gene was confirmed collectively by biochemical and molecular studies. Insilico analysis (PolyPhen-2, Provean, Mutation Taster) predicted the variant to be severe disease causing. Multiple sequence alignment demonstrated the conservation of p. Thr905 across the species. The impact of the mutation on the protein structure was studied by PyMOL and Swiss Protein databank viewer.

Clinical application of a novel next generation sequencing assay for CYP21A2 gene in 310 cases of 21- hydroxylase congenital adrenal hyperplasia from India.

PURPOSE: Accurate diagnosis is required for management of Congenital adrenal hyperplasia (CAH). The conventional method for detection of mutations in the CYP21A2 gene is targeted capillary sequencing which is labor intensive and has limited multiplexing capability. Next generation sequencing (NGS) provides data with high sequence coverage and depth. Our objective was to develop an accurate NGS-based assay to characterize the mutation spectrum in CYP21A2 gene in Indian patients suspected to have 21-OH CAH. METHODS: Cases with 21-OH CAH from 12 endocrine units across India were studied. DNA was extracted from proband's and parent's(subset) blood. Locus-specific long-range PCR and gel electrophoresis of amplicons was followed by NGS where no visible 30 kb homozygous/whole gene deletion was observed. Orthogonal confirmation was performed by capillary sequencing (ABI 3500) and Multiplex Ligation-dependent Probe Amplification (MLPA, MRC-Holland). PCR products were purified and individual libraries were pooled and sequenced (Illumina). RESULTS: Of the 310 CAH cases, biallelic mutations (pathogenic/ likely pathogenic variants involving both CYP21A2 gene copies) were detected in 256 (82.6%), heterozygous mutations in 13 (4.2 %), and none in 41 (13.2%). Most common mutation was c.293-13A/C>G (29.03%), followed by 30 kb deletion (18.24%). Thirty samples tested orthogonally (by capillary sequencing or MLPA) showed 100% concordance with NGS assay. Nine novel variants were identified. CONCLUSIONS: We have developed and validated a comprehensive NGS-based assay for detection of variants in CYP21A2 gene in patients with 21-OH CAH. We describe CYP21A2 mutation spectrum and novel variants in a large cohort of Indian patients with CAH.

Late onset Pompe Disease in India - Beyond the Caucasian phenotype.

We evaluated the clinical histories, motor and pulmonary functions, cardiac phenotypes and GAA genotypes of an Indian cohort of twenty patients with late onset Pompe disease (LOPD) in this multi-centre study. A mean age at onset of symptoms and diagnosis of 9.9 ±â€¯9.7 years and 15.8 ±â€¯12.1 years respectively was identified. All patients had lower extremity limb-girdle muscle weakness. Seven required ventilatory support and seven used mobility assists. Of the four who used both assists, two received ventilatory support prior to wheelchair use. Cardiac involvement was seen in eight patients with various combinations of left ventricular hypertrophy, tricuspid regurgitation, cardiomyopathy, dilated ventricles with biventricular dysfunction and aortic regurgitation. Amongst 20 biochemically diagnosed patients (low residual GAA enzyme activity) GAA genotypes of 19 patients identified homozygous variants in eight and compound heterozygous in 11: 27 missense, 3 nonsense, 2 initiator codon, 3 splice site and one deletion. Nine variants in 7 patients were novel. The leaky Caucasian, splice site LOPD variant, c.-32-13T>G mutation was absent. This first study from India provides an insight into a more severe LOPD phenotype with earlier disease onset at 9.9 years compared to 33.3 years in Caucasian patients, and cardiac involvement more than previously reported. The need for improvement in awareness and diagnosis of LOPD in India is highlighted.

Comprehensive Genetic Analysis Reveals Complexity of Monogenic Urinary Stone Disease.

INTRODUCTION: Because of phenotypic overlap between monogenic urinary stone diseases (USD), gene-specific analyses can result in missed diagnoses. We used targeted next generation sequencing (tNGS), including known and candidate monogenic USD genes, to analyze suspected primary hyperoxaluria (PH) or Dent disease (DD) patients genetically unresolved (negative; N) after Sanger analysis of the known genes. Cohorts consisted of 285 PH (PHN) and 59 DD (DDN) families. METHODS: Variants were assessed using disease-specific and population databases plus variant assessment tools and categorized using the American College of Medical Genetics (ACMG) guidelines. Prior Sanger analysis identified 47 novel PH or DD gene pathogenic variants. RESULTS: Screening by tNGS revealed pathogenic variants in 14 known monogenic USD genes, accounting for 45 families (13.1%), 27 biallelic and 18 monoallelic, including 1 family with a copy number variant (CNV). Recurrent genes included the following: SLC34A3 (n = 13), CLDN16 (n = 8), CYP24A1 (n = 4), SLC34A1 (n = 3), SLC4A1 (n = 3), APRT (n = 2), CLDN19 (n = 2), HNF4A1 (n = 2), and KCNJ1 (n = 2), whereas ATP6V1B1, CASR, and SLC12A1 and missed CNVs in the PH genes AGXT and GRHPR accounted for 1 pedigree each. Of the 48 defined pathogenic variants, 27.1% were truncating and 39.6% were novel. Most patients were diagnosed before 18 years of age (76.1%), and 70.3% of biallelic patients were homozygous, mainly from consanguineous families. CONCLUSION: Overall, in patients suspected of DD or PH, 23.9% and 7.3% of cases, respectively, were caused by pathogenic variants in other genes. This study shows the value of a tNGS screening approach to increase the diagnosis of monogenic USD, which can optimize therapies and facilitate enrollment in clinical trials.