AHDC1 missense mutations in Xia-Gibbs syndrome
Khayat MM, Hu J, Jiang Y, Li H, Chander V, Dawood M, Hansen AW, Li S, Friedman J, Cross L, Bijlsma EK, Ruivenkamp CAL, Sansbury FH, Innis JW, O’Shea JO, Meng Q, Rosenfeld JA, McWalter K, Wangler MF, Lupski JR, Posey JE, Murdock D, Gibbs RA.
HGG Adv. 2021 Oct 14;2(4):100049. doi: 10.1016/j.xhgg.2021.100049. Epub 2021 Aug 10.
Xia-Gibbs syndrome (XGS; MIM: 615829) is a phenotypically heterogeneous neurodevelopmental disorder (NDD) caused by newly arising mutations in the AT-Hook DNA-Binding Motif-Containing 1 (AHDC1) gene that are predicted to lead to truncated AHDC1 protein synthesis. More than 270 individuals have been diagnosed with XGS worldwide. Despite the absence of an independent assay for AHDC1 protein function to corroborate potential functional consequences of rare variant genetic findings, there are also reports of individuals with XGS-like trait manifestations who have de novo missense AHDC1 mutations and who have been provided a molecular diagnosis of the disorder. To investigate a potential contribution of missense mutations to XGS, we mapped the missense mutations from 10 such individuals to the AHDC1 conserved protein domain structure and detailed the observed phenotypes. Five newly identified individuals were ascertained from a local XGS Registry, and an additional five were taken from external reports or databases, including one publication. Where clinical data were available, individuals with missense mutations all displayed phenotypes consistent with those observed in individuals with AHDC1 truncating mutations, including delayed motor milestones, intellectual disability (ID), hypotonia, and speech delay. A subset of the 10 reported missense mutations cluster in two regions of the AHDC1 protein with known conserved domains, likely representing functional motifs. Variants outside the clustered regions score lower for computational prediction of their likely damaging effects. Overall, de novo missense variants in AHDC1 are likely diagnostic of XGS when in silico analysis of their position relative to conserved regions is considered together with disease trait manifestations.
December 28, 2021
Characterization of a patient-derived variant of GPX4 for precision therapy
Liu H, Forouhar F, Seibt T, Saneto R, Wigby K, Friedman J, Xia X, Shchepinov MS, Ramesh SK, Conrad M, Stockwell BR.
Nat Chem Biol. 2021 Dec 20. doi: 10.1038/s41589-021-00915-2. Online ahead of print.
Glutathione peroxidase 4 (GPX4), as the only enzyme in mammals capable of reducing esterified phospholipid hydroperoxides within a cellular context, protects cells from ferroptosis. We identified a homozygous point mutation in the GPX4 gene, resulting in an R152H coding mutation, in three patients with Sedaghatian-type spondylometaphyseal dysplasia. Using structure-based analyses and cell models, including patient fibroblasts, of this variant, we found that the missense variant destabilized a critical loop, which disrupted the active site and caused a substantial loss of enzymatic function. We also found that the R152H variant of GPX4 is less susceptible to degradation, revealing the degradation mechanism of the GPX4 protein. Proof-of-concept therapeutic treatments, which overcome the impaired R152H GPX4 activity, including selenium supplementation, selective antioxidants and a deuterated polyunsaturated fatty acid were identified. In addition to revealing a general approach to investigating rare genetic diseases, we demonstrate the biochemical foundations of therapeutic strategies targeting GPX4.
December 28, 2021
Development of therapies for rare genetic disorders of GPX4: roadmap and opportunities
Cheff DM, Muotri AR, Stockwell BR, Schmidt EE, Ran Q, Kartha RV, Johnson SC, Mittal P, Arnér ESJ, Wigby KM, Hall MD, Ramesh SK
Orphanet J Rare Dis. 2021 Oct 23;16(1):446. doi: 10.1186/s13023-021-02048-0.
BACKGROUND: Extremely rare progressive diseases like Sedaghatian-type Spondylometaphyseal Dysplasia (SSMD) can be neonatally lethal and therefore go undiagnosed or are difficult to treat. Recent sequencing efforts have linked this disease to mutations in GPX4, with consequences in the resulting enzyme, glutathione peroxidase 4. This offers potential diagnostic and therapeutic avenues for those suffering from this disease, though the steps toward these treatments is often convoluted, expensive, and time-consuming.
MAIN BODY: The CureGPX4 organization was developed to promote awareness of GPX4-related diseases like SSMD, as well as support research that could lead to essential therapeutics for patients. We provide an overview of the 21 published SSMD cases and have compiled additional sequencing data for four previously unpublished individuals to illustrate the genetic component of SSMD, and the role of sequencing data in diagnosis. We outline in detail the steps CureGPX4 has taken to reach milestones of team creation, disease understanding, drug repurposing, and design of future studies.
CONCLUSION: The primary aim of this review is to provide a roadmap for therapy development for rare, ultra-rare, and difficult to diagnose diseases, as well as increase awareness of the genetic component of SSMD. This work will offer a better understanding of GPx4-related diseases, and help guide researchers, clinicians, and patients interested in other rare diseases find a path towards treatments.
October 26, 2021
Artificial intelligence enables comprehensive genome interpretation and nomination of candidate diagnoses for rare genetic diseases
De La Vega FM, Chowdhury S, Moore B, Frise E, McCarthy J, Hernandez EJ, Wong T, James K, Guidugli L, Agrawal PB, Genetti CA, Brownstein CA, Beggs AH, Löscher BS, Franke A, Boone B, Levy SE, Õunap K, Pajusalu S, Huentelman M, Ramsey K, Naymik M, Narayanan V, Veeraraghavan N, Billings P, Reese MG, Yandell M, Kingsmore SF.
Genome Med. 2021 Oct 14;13(1):153. doi: 10.1186/s13073-021-00965-0.
BACKGROUND: Clinical interpretation of genetic variants in the context of the patient’s phenotype is becoming the largest component of cost and time expenditure for genome-based diagnosis of rare genetic diseases. Artificial intelligence (AI) holds promise to greatly simplify and speed genome interpretation by integrating predictive methods with the growing knowledge of genetic disease. Here we assess the diagnostic performance of Fabric GEM, a new, AI-based, clinical decision support tool for expediting genome interpretation.
METHODS: We benchmarked GEM in a retrospective cohort of 119 probands, mostly NICU infants, diagnosed with rare genetic diseases, who received whole-genome or whole-exome sequencing (WGS, WES). We replicated our analyses in a separate cohort of 60 cases collected from five academic medical centers. For comparison, we also analyzed these cases with current state-of-the-art variant prioritization tools. Included in the comparisons were trio, duo, and singleton cases. Variants underpinning diagnoses spanned diverse modes of inheritance and types, including structural variants (SVs). Patient phenotypes were extracted from clinical notes by two means: manually and using an automated clinical natural language processing (CNLP) tool. Finally, 14 previously unsolved cases were reanalyzed.
RESULTS: GEM ranked over 90% of the causal genes among the top or second candidate and prioritized for review a median of 3 candidate genes per case, using either manually curated or CNLP-derived phenotype descriptions. Ranking of trios and duos was unchanged when analyzed as singletons. In 17 of 20 cases with diagnostic SVs, GEM identified the causal SVs as the top candidate and in 19/20 within the top five, irrespective of whether SV calls were provided or inferred ab initio by GEM using its own internal SV detection algorithm. GEM showed similar performance in absence of parental genotypes. Analysis of 14 previously unsolved cases resulted in a novel finding for one case, candidates ultimately not advanced upon manual review for 3 cases, and no new findings for 10 cases.
CONCLUSIONS: GEM enabled diagnostic interpretation inclusive of all variant types through automated nomination of a very short list of candidate genes and disorders for final review and reporting. In combination with deep phenotyping by CNLP, GEM enables substantial automation of genetic disease diagnosis, potentially decreasing cost and expediting case review.
October 14, 2021
Insights into the expanding phenotypic spectrum of inherited disorders of biogenic amines
Kuseyri Hübschmann O, Horvath G, Cortès-Saladelafont E, Yıldız Y, Mastrangelo M, Pons R, Friedman J, Mercimek-Andrews S, Wong SN, Pearson TS, Zafeiriou DI, Kulhánek J, Kurian MA, López-Laso E, Oppebøen M, Kılavuz S, Wassenberg T, Goez H, Scholl-Bürgi S, Porta F, Honzík T, Santer R, Burlina A, Sivri HS, Leuzzi V, Hoffmann GF, Jeltsch K, Hübschmann D, Garbade SF; iNTD Registry Study Group, García-Cazorla A, Opladen T.
Nat Commun. 2021 Sep 20;12(1):5529. doi: 10.1038/s41467-021-25515-5.
Inherited disorders of neurotransmitter metabolism are rare neurodevelopmental diseases presenting with movement disorders and global developmental delay. This study presents the results of the first standardized deep phenotyping approach and describes the clinical and biochemical presentation at disease onset as well as diagnostic approaches of 275 patients from the registry of the International Working Group on Neurotransmitter related Disorders. The results reveal an increased rate of prematurity, a high risk for being small for gestational age and for congenital microcephaly in some disorders. Age at diagnosis and the diagnostic delay are influenced by the diagnostic methods applied and by disease-specific symptoms. The timepoint of investigation was also a significant factor: delay to diagnosis has decreased in recent years, possibly due to novel diagnostic approaches or raised awareness. Although each disorder has a specific biochemical pattern, we observed confounding exceptions to the rule. The data provide comprehensive insights into the phenotypic spectrum of neurotransmitter disorders.
September 23, 2021
Commentary: Galactosemia Diagnosis by Whole Exome Sequencing Later in Life
Friedman J, Lucas-Del-Pozo S, Moreno-Martinez D, Camprodon-Gomez M, Moreno-Martinez D, Hernandez-Vara J, Kurian MA.
September 16, 2021
Maternal Smoking and Congenital Heart Defects, National Birth Defects Prevention Study, 1997-2011
Bolin EH, Gokun Y, Romitti PA, Tinker SC, Summers AD, Roberson PK, Hobbs CA, Malik S, Botto LD, Nembhard WN
J Pediatr. 2021 Sep 8:S0022-3476(21)00877-5. doi: 10.1016/j.jpeds.2021.09.005. Online ahead of print.
OBJECTIVES: To assess associations between maternal smoking and congenital heart defects (CHDs) in offspring.
STUDY DESIGN: We performed a retrospective case-control study using data for cases of CHD (n=8,339) and non-malformed controls (n=11,020) children from all years (1997-2011) of the National Birth Defects Prevention Study. Maternal self-reported smoking one month before through three months after conception was evaluated as a binary (none, any) and categorical (light, medium, heavy) exposure. Multivariable logistic regression was used to estimate adjusted odds ratios (aOR) and 95% confidence intervals. Stratified analyses were performed for septal defects according to maternal age, pre-pregnancy body mass index, and maternal race/ethnicity.
RESULTS: Multiple CHDs displayed modest associations with any level of maternal periconceptional smoking independent of potential confounders; the strongest associations were for aggregated septal defects (OR 1.5 [1.3-1.7]), tricuspid atresia (OR 1.7 [1.0-2.7]), and double outlet right ventricle (DORV) (1.5 [1.1-2.1]). TA and DORV also displayed dose-response relationships. Among heavy smokers, the highest odds were again observed for TA (aOR 3.0 [1.5-6.1]) and DORV (aOR 1.5 [1.1-2.2]). Heavy smokers ≥35 years old more frequently had a child with a septal defect when compared with similarly aged non-smokers (aOR 2.3 [1.4-3.9]).
CONCLUSIONS: Maternal periconceptional smoking is most strongly associated with septal defects, TA and DORV; the risk for septal defects is modified by maternal age.
September 16, 2021
To Be or No B2: A Rare Cause of Stridor and Weakness in a Toddler
Aliya L. Frederick, MD, PhD, Jennifer H. Yang, MD, Sarah Schneider, MD, Alexis Quade, MD, Lucia Guidugli, PhD, CGMBS, Kristen Wigby, MD, Melissa Cameron, MD
Child Neurol Open. 2021 Aug 5;8:2329048X211030723. doi: 10.1177/2329048X211030723. eCollection 2021 Jan-Dec.
We present a case of a young child with a rare metabolic disorder whose clinical presentation resembled that of autoimmune myasthenia gravis. The differential diagnosis was expanded when autoantibody testing was negative and the patient did not respond to standard immunomodulatory therapies. Rapid whole genome sequencing identified 2 rare variants of uncertain significance in the SLC52A3 gene shown to be in compound heterozygous state after parental testing. Biallelic mutations in SLC52A3 are associated with Riboflavin Transporter Deficiency, which in its untreated form, results in progressive neurodegeneration and death. Supplementation with oral riboflavin has been shown to limit disease progression and improve symptoms in some patients. When the diagnosis is suspected, patients should be started on supplementation immediately while awaiting results from genetic studies.
August 17, 2021
Exome sequencing of child-parent trios with bladder exstrophy: Findings in 26 children
Pitsava G, Feldkamp ML, Pankratz N, Lane J, Kay DM, Conway KM, Shaw GM, Reefhuis J, Jenkins MM, Almli LM, Olshan AF, Pangilinan F, Brody LC, Sicko RJ, Hobbs CA, Bamshad M, McGoldrick D, Nickerson DA, Finnell RH, Mullikin J, Romitti PA, Mills JL
Am J Med Genet A. 2021 Aug 5. doi: 10.1002/ajmg.a.62439. Online ahead of print.
Bladder exstrophy (BE) is a rare, lower ventral midline defect with the bladder and part of the urethra exposed. The etiology of BE is unknown but thought to be influenced by genetic variation with more recent studies suggesting a role for rare variants. As such, we conducted paired-end exome sequencing in 26 child/mother/father trios. Three children had rare (allele frequency ≤ 0.0001 in several public databases) inherited variants in TSPAN4, one with a loss-of-function variant and two with missense variants. Two children had loss-of-function variants in TUBE1. Four children had rare missense or nonsense variants (one per child) in WNT3, CRKL, MYH9, or LZTR1, genes previously associated with BE. We detected 17 de novo missense variants in 13 children and three de novo loss-of-function variants (AKR1C2, PRRX1, PPM1D) in three children (one per child). We also detected rare compound heterozygous loss-of-function variants in PLCH2 and CLEC4M and rare inherited missense or loss-of-function variants in additional genes applying autosomal recessive (three genes) and X-linked recessive inheritance models (13 genes). Variants in two genes identified may implicate disruption in cell migration (TUBE1) and adhesion (TSPAN4) processes, mechanisms proposed for BE, and provide additional evidence for rare variants in the development of this defect.
August 9, 2021
Gene DiscoveryRare Disease
Use of Metagenomic Next-Generation Sequencing to Identify Pathogens in Pediatric Osteoarticular Infections
Ramchandar N, Burns J, Coufal NG, Pennock A, Briggs B, Stinnett R, Bradley J, Arnold J, Liu GY, Pring M, Upasani VV, Rickert K, Dimmock D, Chiu C, Farnaes L, Cannavino C.
Open Forum Infect Dis. 2021 Jul 17;8(7):ofab346. doi: 10.1093/ofid/ofab346. eCollection 2021 Jul.
BACKGROUND: Osteoarticular infections (OAIs) are frequently encountered in children. Treatment may be guided by isolation of a pathogen; however, operative cultures are often negative. Metagenomic next-generation sequencing (mNGS) allows for broad and sensitive pathogen detection that is culture-independent. We sought to evaluate the diagnostic utility of mNGS in comparison to culture and usual care testing to detect pathogens in acute osteomyelitis and/or septic arthritis in children.
METHODS: This was a single-site study to evaluate the use of mNGS in comparison to culture to detect pathogens in acute pediatric osteomyelitis and/or septic arthritis. Subjects admitted to a tertiary children’s hospital with suspected OAI were eligible for enrollment. We excluded subjects with bone or joint surgery within 30 days of admission or with chronic osteomyelitis. Operative samples were obtained at the surgeon’s discretion per standard care (fluid or tissue) and based on imaging and operative findings. We compared mNGS to culture and usual care testing (culture and polymerase chain reaction [PCR]) from the same site.
RESULTS: We recruited 42 subjects over the enrollment period. mNGS of the operative samples identified a pathogen in 26 subjects compared to 19 subjects in whom culture identified a pathogen. In 4 subjects, mNGS identified a pathogen where combined usual care testing (culture and PCR) was negative. Positive predictive agreement and negative predictive agreement both were 93.0% for mNGS.
CONCLUSIONS: In this single-site prospective study of pediatric OAI, we demonstrated the diagnostic utility of mNGS testing in comparison to culture and usual care (culture and PCR) from operative specimens.
July 30, 2021