Prospective cohort study of genomic newborn screening: BabyScreen+ pilot study protocol.

INTRODUCTION: Newborn bloodspot screening (NBS) is a highly successful public health programme that uses biochemical and other assays to screen for severe but treatable childhood-onset conditions. Introducing genomic sequencing into NBS programmes increases the range of detectable conditions but raises practical and ethical issues. Evidence from prospectively ascertained cohorts is required to guide policy and future implementation. This study aims to develop, implement and evaluate a genomic NBS (gNBS) pilot programme. METHODS AND ANALYSIS: The BabyScreen+ study will pilot gNBS in three phases. In the preimplementation phase, study materials, including education resources, decision support and data collection tools, will be designed. Focus groups and key informant interviews will also be undertaken to inform delivery of the study and future gNBS programmes. During the implementation phase, we will prospectively recruit birth parents in Victoria, Australia, to screen 1000 newborns for over 600 severe, treatable, childhood-onset conditions. Clinically accredited whole genome sequencing will be performed following standard NBS using the same sample. High chance results will be returned by genetic healthcare professionals, with follow-on genetic and other confirmatory testing and referral to specialist services as required. The postimplementation phase will evaluate the feasibility of gNBS as the primary aim, and assess ethical, implementation, psychosocial and health economic factors to inform future service delivery. ETHICS AND DISSEMINATION: This project received ethics approval from the Royal Children's Hospital Melbourne Research Ethics Committee: HREC/91500/RCHM-2023, HREC/90929/RCHM-2022 and HREC/91392/RCHM-2022. Findings will be disseminated to policy-makers, and through peer-reviewed journals and conferences.

The cost of proband and trio exome and genome analysis in rare disease: A micro-costing study.

PURPOSE: Rare disease genomic testing is a complex process involving various resources. Accurate resource estimation is required for informed prioritization and reimbursement decisions. This study aims to analyze the costs and cost drivers of clinical genomic testing. METHODS: Based on genomic sequencing workflows we microcosted limited virtual panel analysis on exome sequencing backbone, proband and trio exome, and genome testing for proband and trio analysis in 2023 Australian Dollars ($). Deterministic and probabilistic sensitivity analyses were undertaken. RESULTS: Panel testing costs AUD $2373 ($733-$6166), and exome sequencing costs $2823 ($802-$7206) and $5670 ($2006-$11,539) for proband and trio analysis, respectively. Genome sequencing costs $4840 ($2153-$9890) and $11,589 ($5842-$16,562) for proband and trio analysis. The most expensive cost component of genomic testing was sequencing (36.9%-69.4% of total cost), with labor accounting for 27.1%-63.2% of total cost. CONCLUSION: We provide a comprehensive analysis of rare disease genomic testing costs, for a range of clinical testing types and contexts. This information will accurately inform economic evaluations of rare disease genomic testing and decision making on policy settings that assist with implementation, such as genomic testing reimbursement.

Variants in SART3 cause a spliceosomopathy characterised by failure of testis development and neuronal defects.

Squamous cell carcinoma antigen recognized by T cells 3 (SART3) is an RNA-binding protein with numerous biological functions including recycling small nuclear RNAs to the spliceosome. Here, we identify recessive variants in SART3 in nine individuals presenting with intellectual disability, global developmental delay and a subset of brain anomalies, together with gonadal dysgenesis in 46,XY individuals. Knockdown of the Drosophila orthologue of SART3 reveals a conserved role in testicular and neuronal development. Human induced pluripotent stem cells carrying patient variants in SART3 show disruption to multiple signalling pathways, upregulation of spliceosome components and demonstrate aberrant gonadal and neuronal differentiation in vitro. Collectively, these findings suggest that bi-allelic SART3 variants underlie a spliceosomopathy which we tentatively propose be termed INDYGON syndrome (Intellectual disability, Neurodevelopmental defects and Developmental delay with 46,XY GONadal dysgenesis). Our findings will enable additional diagnoses and improved outcomes for individuals born with this condition.

Integrated multi-omics for rapid rare disease diagnosis on a national scale.

Critically ill infants and children with rare diseases need equitable access to rapid and accurate diagnosis to direct clinical management. Over 2 years, the Acute Care Genomics program provided whole-genome sequencing to 290 families whose critically ill infants and children were admitted to hospitals throughout Australia with suspected genetic conditions. The average time to result was 2.9 d and diagnostic yield was 47%. We performed additional bioinformatic analyses and transcriptome sequencing in all patients who remained undiagnosed. Long-read sequencing and functional assays, ranging from clinically accredited enzyme analysis to bespoke quantitative proteomics, were deployed in selected cases. This resulted in an additional 19 diagnoses and an overall diagnostic yield of 54%. Diagnostic variants ranged from structural chromosomal abnormalities through to an intronic retrotransposon, disrupting splicing. Critical care management changed in 120 diagnosed patients (77%). This included major impacts, such as informing precision treatments, surgical and transplant decisions and palliation, in 94 patients (60%). Our results provide preliminary evidence of the clinical utility of integrating multi-omic approaches into mainstream diagnostic practice to fully realize the potential of rare disease genomic testing in a timely manner.

FGF9 variant in 46,XY DSD patient suggests a role for dimerization in sex determination.

46,XY gonadal dysgenesis (GD) is a Disorder/Difference of Sex Development (DSD) that can present with phenotypes ranging from ambiguous genitalia to complete male-to-female sex reversal. Around 50% of 46,XY DSD cases receive a molecular diagnosis. In mice, Fibroblast growth factor 9 (FGF9) is an important component of the male sex-determining pathway. Two FGF9 variants reported to date disrupt testis development in mice, but not in humans. Here, we describe a female patient with 46,XY GD harbouring the rare FGF9 variant (missense mutation), NM_002010.2:c.583G > A;p.(Asp195Asn) (D195N). By biochemical and cell-based approaches, the D195N variant disrupts FGF9 protein homodimerisation and FGF9-heparin-binding, and reduces both Sertoli cell proliferation and Wnt4 repression. XY Fgf9D195N/D195N foetal mice show a transient disruption of testicular cord development, while XY Fgf9D195N/- foetal mice show partial male-to-female gonadal sex reversal. In the general population, the D195N variant occurs at an allele frequency of 2.4 × 10-5 , suggesting an oligogenic basis for the patient's DSD. Exome analysis of the patient reveals several known and novel variants in genes expressed in human foetal Sertoli cells at the time of sex determination. Taken together, our results indicate that disruption of FGF9 homodimerization impairs testis determination in mice and, potentially, also in humans in combination with other variants.

Aberrant splicing and transcriptional activity of TPP1 result in CLN2-like disorder.

RNA sequencing (RNAseq) is emerging as a complementary tool to DNA sequencing, providing utility in diagnosis for disorders such as neuronal ceroid lipofuscinosis CLN2 disease. We describe an individual with a presentation suggestive of an attenuated CLN2 phenotype, including a history of regression, recent-onset microcephaly and spasticity from age five years. Exome sequencing revealed two variants inherited in trans in TPP1, NM_000391.4:c.225A>G; p.(Gln75 = ) and NM_000391.4:c.1012C>G; p.(Gln338Glu), both classified as variants of uncertain significance. TPP1 activity was found to be significantly reduced in fibroblasts of the affected individual. RNAseq was performed to assess the impact of compound heterozygous variants in TPP1 and enabled the identification of three aberrant splicing events. The c.225A>G variant introduces a 5 nucleotide truncation of exon 3 and a loss of reading frame. The majority of CLN2 transcripts exclude either exon 8 or exons 7-8, resulting in large in-frame deletions. Isoform specific RT-PCR confirmed the aberrant splicing events are mutually exclusive, suggesting that the paternal exon 8 c.1012C>G variant results in exon skipping. This case study demonstrates how RNAseq can be used as an orthogonal test to inform the interpretation of some variants of unknown significance and its particular importance in disorders where effective disease management requires early diagnosis.

The severe epilepsy syndromes of infancy: A population-based study.

OBJECTIVE: To study the epilepsy syndromes among the severe epilepsies of infancy and assess their incidence, etiologies, and outcomes. METHODS: A population-based cohort study was undertaken of severe epilepsies with onset before age 18 months in Victoria, Australia. Two epileptologists reviewed clinical features, seizure videos, and electroencephalograms to diagnose International League Against Epilepsy epilepsy syndromes. Incidence, etiologies, and outcomes at age 2 years were determined. RESULTS: Seventy-three of 114 (64%) infants fulfilled diagnostic criteria for epilepsy syndromes at presentation, and 16 (14%) had "variants" of epilepsy syndromes in which there was one missing or different feature, or where all classical features had not yet emerged. West syndrome (WS) and "WS-like" epilepsy (infantile spasms without hypsarrhythmia or modified hypsarrhythmia) were the most common syndromes, with a combined incidence of 32.7/100 000 live births/year. The incidence of epilepsy of infancy with migrating focal seizures (EIMFS) was 4.5/100 000 and of early infantile epileptic encephalopathy (EIEE) was 3.6/100 000. Structural etiologies were common in "WS-like" epilepsy (100%), unifocal epilepsy (83%), and WS (39%), whereas single gene disorders predominated in EIMFS, EIEE, and Dravet syndrome. Eighteen (16%) infants died before age 2 years. Development was delayed or borderline in 85 of 96 (89%) survivors, being severe-profound in 40 of 96 (42%). All infants with EIEE or EIMFS had severe-profound delay or were deceased, but only 19 of 64 (30%) infants with WS, "WS-like," or "unifocal epilepsy" had severe-profound delay, and only two of 64 (3%) were deceased. SIGNIFICANCE: Three quarters of severe epilepsies of infancy could be assigned an epilepsy syndrome or "variant syndrome" at presentation. In this era of genomic testing and advanced brain imaging, diagnosing epilepsy syndromes at presentation remains clinically useful for guiding etiologic investigation, initial treatment, and prognostication.

Feasibility of Ultra-Rapid Exome Sequencing in Critically Ill Infants and Children With Suspected Monogenic Conditions in the Australian Public Health Care System.

Importance: Widespread adoption of rapid genomic testing in pediatric critical care requires robust clinical and laboratory pathways that provide equitable and consistent service across health care systems. Objective: To prospectively evaluate the performance of a multicenter network for ultra-rapid genomic diagnosis in a public health care system. Design, Setting, and Participants: Descriptive feasibility study of critically ill pediatric patients with suspected monogenic conditions treated at 12 Australian hospitals between March 2018 and February 2019, with data collected to May 2019. A formal implementation strategy emphasizing communication and feedback, standardized processes, coordination, distributed leadership, and collective learning was used to facilitate adoption. Exposures: Ultra-rapid exome sequencing. Main Outcomes and Measures: The primary outcome was time from sample receipt to ultra-rapid exome sequencing report. The secondary outcomes were the molecular diagnostic yield, the change in clinical management after the ultra-rapid exome sequencing report, the time from hospital admission to the laboratory report, and the proportion of laboratory reports returned prior to death or hospital discharge. Results: The study population included 108 patients with a median age of 28 days (range, 0 days to 17 years); 34% were female; and 57% were from neonatal intensive care units, 33% were from pediatric intensive care units, and 9% were from other hospital wards. The mean time from sample receipt to ultra-rapid exome sequencing report was 3.3 days (95% CI, 3.2-3.5 days) and the median time was 3 days (range, 2-7 days). The mean time from hospital admission to ultra-rapid exome sequencing report was 17.5 days (95% CI, 14.6-21.1 days) and 93 reports (86%) were issued prior to death or hospital discharge. A molecular diagnosis was established in 55 patients (51%). Eleven diagnoses (20%) resulted from using the following approaches to augment standard exome sequencing analysis: mitochondrial genome sequencing analysis, exome sequencing-based copy number analysis, use of international databases to identify novel gene-disease associations, and additional phenotyping and RNA analysis. In 42 of 55 patients (76%) with a molecular diagnosis and 6 of 53 patients (11%) without a molecular diagnosis, the ultra-rapid exome sequencing result was considered as having influenced clinical management. Targeted treatments were initiated in 12 patients (11%), treatment was redirected toward palliative care in 14 patients (13%), and surveillance for specific complications was initiated in 19 patients (18%). Conclusions and Relevance: This study suggests feasibility of ultra-rapid genomic testing in critically ill pediatric patients with suspected monogenic conditions in the Australian public health care system. However, further research is needed to understand the clinical value of such testing, and the generalizability of the findings to other health care settings.

Bi-allelic LoF NRROS Variants Impairing Active TGF-ß1 Delivery Cause a Severe Infantile-Onset Neurodegenerative Condition with Intracranial Calcification.

Negative regulator of reactive oxygen species (NRROS) is a leucine-rich repeat-containing protein that uniquely associates with latent transforming growth factor beta-1 (TGF- ß1) and anchors it on the cell surface; this anchoring is required for activation of TGF-ß1 in macrophages and microglia. We report six individuals from four families with bi-allelic variants in NRROS. All affected individuals had neurodegenerative disease with refractory epilepsy, developmental regression, and reduced white matter volume with delayed myelination. The clinical course in affected individuals began with normal development or mild developmental delay, and the onset of seizures occurred within the first year of life, followed by developmental regression. Intracranial calcification was detected in three individuals. The phenotypic features in affected individuals are consistent with those observed in the Nrros knockout mouse, and they overlap with those seen in the human condition associated with TGF-ß1 deficiency. The disease-causing NRROS variants involve two significant functional NRROS domains. These variants result in aberrant NRROS proteins with impaired ability to anchor latent TGF-ß1 on the cell surface. Using confocal microscopy in HEK293T cells, we demonstrate that wild-type and mutant NRROS proteins co-localize with latent TGF-ß1 intracellularly. However, using flow cytometry, we show that our mutant NRROS proteins fail to anchor latent TGF-ß1 at the cell surface in comparison to wild-type NRROS. Moreover, wild-type NRROS rescues the defect of our disease-associated mutants in presenting latent TGF-ß1 to the cell surface. Taken together, our findings suggest that loss of NRROS function causes a severe childhood-onset neurodegenerative condition with features suggestive of a disordered response to inflammation.

Analysis of variants in GATA4 and FOG2/ZFPM2 demonstrates benign contribution to 46,XY disorders of sex development.

BACKGROUND: GATA-binding protein 4 (GATA4) and Friend of GATA 2 protein (FOG2, also known as ZFPM2) form a heterodimer complex that has been shown to influence transcription of genes in a number of developmental systems. Recent evidence has also shown these genes play a role in gonadal sexual differentiation in humans. Previously we identified four variants in GATA4 and an unexpectedly large number of variants in ZFPM2 in a cohort of individuals with 46,XY Differences/Disorders of Sex Development (DSD) (Eggers et al, Genome Biology, 2016; 17: 243). METHOD: Here, we review variant curation and test the functional activity of GATA4 and ZFPM2 variants. We assess variant transcriptional activity on gonadal specific promoters (Sox9 and AMH) and variant protein-protein interactions. RESULTS: Our findings support that the majority of GATA4 and ZFPM2 variants we identified are benign in their contribution to 46,XY DSD. Indeed, only one variant, in the conserved N-terminal zinc finger of GATA4, was considered pathogenic, with functional analysis confirming differences in its ability to regulate Sox9 and AMH and in protein interaction with ZFPM2. CONCLUSIONS: Our study helps define the genetic factors contributing to 46,XY DSD and suggests that the majority of variants we identified in GATA4 and ZFPM2/FOG2 are not causative.

The association between pneumococcal vaccination, ethnicity, and the nasopharyngeal microbiota of children in Fiji.

BACKGROUND: Streptococcus pneumoniae is a significant global pathogen that colonises the nasopharynx of healthy children. Pneumococcal conjugate vaccines, which reduce nasopharyngeal colonisation of vaccine-type S. pneumoniae, may have broader effects on the nasopharyngeal microbiota; however, data are limited. In Fiji, nasopharyngeal carriage prevalence of S. pneumoniae and other colonising species differ between the two main ethnic groups. Here, we examined the association between the 7-valent pneumococcal conjugate vaccine (PCV7) and the nasopharyngeal microbiota of children in Fiji, including for each of the two main ethnic groups-indigenous Fijians (iTaukei) and Fijians of Indian descent (FID). METHOD: The nasopharyngeal microbiota of 132 Fijian children was examined using nasopharyngeal swabs collected from 12-month-old iTaukei and FID children who were vaccinated (3 doses PCV7) or unvaccinated in infancy as part of a phase II randomised controlled trial. Microbiota composition was determined by sequencing the V4 region of the 16S rRNA gene. Species-specific carriage of S. pneumoniae, Haemophilus influenzae, Moraxella catarrhalis and Staphylococcus aureus was determined using real-time quantitative PCR. Associations between microbiota composition and other host and environmental factors were considered in the analysis. RESULTS: PCV7 had no overall impact on microbial diversity or composition. However, ethnic differences were observed in both diversity and composition with iTaukei children having higher relative abundance of Moraxella (p = 0.004) and Haemophilus (p = 0.004) and lower relative abundance of Staphylococcus (p = 0.026), Dolosigranulum (p = 0.004) and Corynebacterium (p = 0.003) compared with FID children. Further, when we stratified by ethnicity, associations with PCV7 could be detected: vaccinated iTaukei children had a lower relative abundance of Streptococcus and Haemophilus compared with unvaccinated iTaukei children (p = 0.022 and p = 0.043, respectively); and vaccinated FID children had a higher relative abundance of Dolosigranulum compared with unvaccinated FID children (p = 0.037). Children with symptoms of an upper respiratory tract infection (URTI) had a significantly different microbiota composition to children without symptoms. The microbiota composition of iTaukei children without URTI symptoms was most similar to the microbiota composition of FID children with URTI symptoms. CONCLUSIONS: Associations between PCV7 and nasopharyngeal microbiota differed within each ethnic group. This study highlights the influence that ethnicity and URTIs have on nasopharyngeal microbiota.

Early diagnosis of Pearson syndrome in neonatal intensive care following rapid mitochondrial genome sequencing in tandem with exome sequencing.

Rapid genomic testing is a valuable new diagnostic tool for acutely unwell infants, however exome sequencing does not deliver clinical-grade mitochondrial genome sequencing and may fail to diagnose mitochondrial disorders caused by mitochondrial DNA (mtDNA) variants. Rapid mitochondrial genome sequencing and analysis are not routinely available in rapid genomic diagnosis programmes. We present two critically ill neonates with transfusion-dependent anaemia and persistent lactic acidosis who underwent rapid mitochondrial genome sequencing in tandem with exome sequencing as part of an exome sequencing-based rapid genomic diagnosis programme. No diagnostic variants were identified on examination of the nuclear exome data for either infant. Mitochondrial genome sequencing identified a large mtDNA deletion in both infants, diagnosing Pearson syndrome within 74 and 55 h, respectively. Early diagnosis in the third week of life allowed the avoidance of a range of other investigations and appropriate treatment planning. Rapid mitochondrial genome analysis provides additional diagnostic and clinical utility and should be considered as an adjunct to exome sequencing in rapid genomic diagnosis programmes.

NR5A1 gene variants repress the ovarian-specific WNT signaling pathway in 46,XX disorders of sex development patients.

Several recent reports have described a missense variant in the gene NR5A1 (c.274C>T; p.Arg92Trp) in a significant number of 46,XX ovotesticular or testicular disorders of sex development (DSDs) cases. The affected residue falls within the DNA-binding domain of the NR5A1 protein, however the exact mechanism by which it causes testicular development in 46,XX individuals remains unclear. We have screened a cohort of 26 patients with 46,XX (ovo)testicular DSD and identified three unrelated individuals with this NR5A1 variant (p.Arg92Trp), as well as one patient with a novel NR5A1 variant (c.779C>T; p.Ala260Val). We examined the functional effect of these changes, finding that while protein levels and localization were unaffected, variant NR5A1 proteins repress the WNT signaling pathway and have less ability to upregulate the anti-testis gene NR0B1. These findings highlight how NR5A1 variants impact ovarian differentiation across multiple pathways, resulting in a switch from ovarian to testis development in genetic females.

Whole exome sequencing reveals a de novo missense variant in EEF1A2 in a Rett syndrome-like patient.

Using whole exome sequencing, we found a pathogenic variant in the EEF1A2 gene in a patient with a Rett syndrome-like (RTT-like) phenotype, further confirming the association between EEF1A2 and Rett syndrome RTT and RTT-like phenotypes.

A population-based cost-effectiveness study of early genetic testing in severe epilepsies of infancy.

OBJECTIVE: The severe epilepsies of infancy (SEI) are a devastating group of disorders that pose a major care and economic burden on society; early diagnosis is critical for optimal management. This study sought to determine the incidence and etiologies of SEI, and model the yield and cost-effectiveness of early genetic testing. METHODS: A population-based study was undertaken of the incidence, etiologies, and cost-effectiveness of a whole exome sequencing-based gene panel (targeted WES) in infants with SEI born during 2011-2013, identified through electroencephalography (EEG) and neonatal databases. SEI was defined as seizure onset before age 18 months, frequent seizures, epileptiform EEG, and failure of ≥2 antiepileptic drugs. Medical records, investigations, MRIs, and EEGs were analyzed, and genetic testing was performed if no etiology was identified. Economic modeling was performed to determine yield and cost-effectiveness of investigation of infants with unknown etiology at epilepsy onset, incorporating targeted WES at different stages of the diagnostic pathway. RESULTS: Of 114 infants with SEI (incidence = 54/100 000 live births/y), the etiology was determined in 76 (67%): acquired brain injuries (n = 14), focal cortical dysplasias (n = 14), other brain malformations (n = 17), channelopathies (n = 11), chromosomal (n = 9), metabolic (n = 6), and other genetic (n = 5) disorders. Modeling showed that incorporating targeted WES increased diagnostic yield compared to investigation without targeted WES (48/86 vs 39/86). Early targeted WES had lower total cost ($677 081 U.S. dollars [USD] vs $738 136 USD) than late targeted WES. A pathway with early targeted WES and limited metabolic testing yielded 7 additional diagnoses compared to investigation without targeted WES (46/86 vs 39/86), with lower total cost ($455 597 USD vs $661 103 USD), lower cost per diagnosis ($9904 USD vs $16 951 USD), and a dominant cost-effectiveness ratio. SIGNIFICANCE: Severe epilepsies occur in 1 in 2000 infants, with the etiology identified in two-thirds, most commonly malformative. Early use of targeted WES yields more diagnoses at lower cost. Early genetic diagnosis will enable timely administration of precision medicines, once developed, with the potential to improve long-term outcome.

Functional characterization of novel NR5A1 variants reveals multiple complex roles in disorders of sex development.

Variants in the NR5A1 gene encoding SF1 have been described in a diverse spectrum of disorders of sex development (DSD). Recently, we reported the use of a targeted gene panel for DSD where we identified 15 individuals with a variant in NR5A1, nine of which are novel. Here, we examine the functional effect of these changes in relation to the patient phenotype. All novel variants tested had reduced trans-activational activity, while several had altered protein level, localization, or conformation. In addition, we found evidence of new roles for SF1 protein domains including a region within the ligand binding domain that appears to contribute to SF1 regulation of Müllerian development. There was little correlation between the severity of the phenotype and the nature of the NR5A1 variant. We report two familial cases of NR5A1 deficiency with evidence of variable expressivity; we also report on individuals with oligogenic inheritance. Finally, we found that the nature of the NR5A1 variant does not inform patient outcomes (including pubertal androgenization and malignancy risk). This study adds nine novel pathogenic NR5A1 variants to the pool of diagnostic variants. It highlights a greater need for understanding the complexity of SF1 function and the additional factors that contribute.

Monoallelic BMP2 Variants Predicted to Result in Haploinsufficiency Cause Craniofacial, Skeletal, and Cardiac Features Overlapping Those of 20p12 Deletions.

Bone morphogenetic protein 2 (BMP2) in chromosomal region 20p12 belongs to a gene superfamily encoding TGF-ß-signaling proteins involved in bone and cartilage biology. Monoallelic deletions of 20p12 are variably associated with cleft palate, short stature, and developmental delay. Here, we report a cranioskeletal phenotype due to monoallelic truncating and frameshift BMP2 variants and deletions in 12 individuals from eight unrelated families that share features of short stature, a recognizable craniofacial gestalt, skeletal anomalies, and congenital heart disease. De novo occurrence and autosomal-dominant inheritance of variants, including paternal mosaicism in two affected sisters who inherited a BMP2 splice-altering variant, were observed across all reported families. Additionally, we observed similarity to the human phenotype of short stature and skeletal anomalies in a heterozygous Bmp2-knockout mouse model, suggesting that haploinsufficiency of BMP2 could be the primary phenotypic determinant in individuals with predicted truncating variants and deletions encompassing BMP2. These findings demonstrate the important role of BMP2 in human craniofacial, skeletal, and cardiac development and confirm that individuals heterozygous for BMP2 truncating sequence variants or deletions display a consistent distinct phenotype characterized by short stature and skeletal and cardiac anomalies without neurological deficits.

XX Disorder of Sex Development is associated with an insertion on chromosome 9 and downregulation of RSPO1 in dogs (Canis lupus familiaris).

Remarkable progress has been achieved in understanding the mechanisms controlling sex determination, yet the cause for many Disorders of Sex Development (DSD) remains unknown. Of particular interest is a rare XX DSD subtype in which individuals are negative for SRY, the testis determining factor on the Y chromosome, yet develop testes or ovotestes, and both of these phenotypes occur in the same family. This is a naturally occurring disorder in humans (Homo sapiens) and dogs (C. familiaris). Phenotypes in the canine XX DSD model are strikingly similar to those of the human XX DSD subtype. The purposes of this study were to identify 1) a variant associated with XX DSD in the canine model and 2) gene expression alterations in canine embryonic gonads that could be informative to causation. Using a genome wide association study (GWAS) and whole genome sequencing (WGS), we identified a variant on C. familiaris autosome 9 (CFA9) that is associated with XX DSD in the canine model and in affected purebred dogs. This is the first marker identified for inherited canine XX DSD. It lies upstream of SOX9 within the canine ortholog for the human disorder, which resides on 17q24. Inheritance of this variant indicates that XX DSD is a complex trait in which breed genetic background affects penetrance. Furthermore, the homozygous variant genotype is associated with embryonic lethality in at least one breed. Our analysis of gene expression studies (RNA-seq and PRO-seq) in embryonic gonads at risk of XX DSD from the canine model identified significant RSPO1 downregulation in comparison to XX controls, without significant upregulation of SOX9 or other known testis pathway genes. Based on these data, a novel mechanism is proposed in which molecular lesions acting upstream of RSPO1 induce epigenomic gonadal mosaicism.

Disorders of sex development: insights from targeted gene sequencing of a large international patient cohort.

BACKGROUND: Disorders of sex development (DSD) are congenital conditions in which chromosomal, gonadal, or phenotypic sex is atypical. Clinical management of DSD is often difficult and currently only 13% of patients receive an accurate clinical genetic diagnosis. To address this we have developed a massively parallel sequencing targeted DSD gene panel which allows us to sequence all 64 known diagnostic DSD genes and candidate genes simultaneously. RESULTS: We analyzed DNA from the largest reported international cohort of patients with DSD (278 patients with 46,XY DSD and 48 with 46,XX DSD). Our targeted gene panel compares favorably with other sequencing platforms. We found a total of 28 diagnostic genes that are implicated in DSD, highlighting the genetic spectrum of this disorder. Sequencing revealed 93 previously unreported DSD gene variants. Overall, we identified a likely genetic diagnosis in 43% of patients with 46,XY DSD. In patients with 46,XY disorders of androgen synthesis and action the genetic diagnosis rate reached 60%. Surprisingly, little difference in diagnostic rate was observed between singletons and trios. In many cases our findings are informative as to the likely cause of the DSD, which will facilitate clinical management. CONCLUSIONS: Our massively parallel sequencing targeted DSD gene panel represents an economical means of improving the genetic diagnostic capability for patients affected by DSD. Implementation of this panel in a large cohort of patients has expanded our understanding of the underlying genetic etiology of DSD. The inclusion of research candidate genes also provides an invaluable resource for future identification of novel genes.