Genome Sequencing for Diagnosing Rare Diseases.

BACKGROUND: Genetic variants that cause rare disorders may remain elusive even after expansive testing, such as exome sequencing. The diagnostic yield of genome sequencing, particularly after a negative evaluation, remains poorly defined. METHODS: We sequenced and analyzed the genomes of families with diverse phenotypes who were suspected to have a rare monogenic disease and for whom genetic testing had not revealed a diagnosis, as well as the genomes of a replication cohort at an independent clinical center. RESULTS: We sequenced the genomes of 822 families (744 in the initial cohort and 78 in the replication cohort) and made a molecular diagnosis in 218 of 744 families (29.3%). Of the 218 families, 61 (28.0%) - 8.2% of families in the initial cohort - had variants that required genome sequencing for identification, including coding variants, intronic variants, small structural variants, copy-neutral inversions, complex rearrangements, and tandem repeat expansions. Most families in which a molecular diagnosis was made after previous nondiagnostic exome sequencing (63.5%) had variants that could be detected by reanalysis of the exome-sequence data (53.4%) or by additional analytic methods, such as copy-number variant calling, to exome-sequence data (10.8%). We obtained similar results in the replication cohort: in 33% of the families in which a molecular diagnosis was made, or 8% of the cohort, genome sequencing was required, which showed the applicability of these findings to both research and clinical environments. CONCLUSIONS: The diagnostic yield of genome sequencing in a large, diverse research cohort and in a small clinical cohort of persons who had previously undergone genetic testing was approximately 8% and included several types of pathogenic variation that had not previously been detected by means of exome sequencing or other techniques. (Funded by the National Human Genome Research Institute and others.).

Unraveling the propensity of various genetic disorders and syndromes in the Koraga, an aboriginal tribe from southern India.

Koragas, recognized as a particularly vulnerable tribal group (PVTG) by the Government of India, are from coastal Karnataka and Kerala. They are experiencing severe socioeconomic and health-related issues and rapid depopulation. The unique genetic makeup of Koragas has been maintained by the practice of endogamy. We aimed to identify genetic factors potentially associated with the predisposition of Koragas towards genetic and multifactorial disorders. We employed genome-wise data of 29 Koraga individuals genotyped on the Infinium Global Screening Array-24 v3.0 BeadChip platform and performed various population genetic analyses including kinship, identity by descent (IBD), and runs of homozygosity (RoH). A high degree of haplotype sharing among the Koraga participants may be indicative of a recent founder event. We identified genetic variants and genes associated with several genetic disorders, higher infant mortality rate, neurological disorders, deafness, and lower fertility rate of this agrarian tribe. Ours is the first genome-wide study on the Koraga tribe that identified genetic factors associated with various genetic disorders. Our findings can provide public healthcare providers with essential genetic information that can be useful in augmenting medical and healthcare services and improving the quality of life of Koragas.

'If I Knew More I Would Feel Less Worried': Filipino Americans' Attitudes and Knowledge of Genetic Disease, Counseling, and Testing.

INTRODUCTION: The field of genetics is rapidly expanding and people are increasingly utilizing genetic testing and counseling services. However, the current literature on genetic health topics and Filipinos remains limited, as many minority populations are not adequately studied. This study describes Filipino Americans' attitudes and knowledge of genetic disease, genetic testing, and genetic counseling. To address these knowledge gaps and reduce the burden of health disparities, the informational needs of Filipino Americans regarding genetic disease and genetic services must be understood in order to better tailor these services and outreach methods. METHODS: Fifteen semi-structured, qualitative interviews were held with individuals who self-identified as Filipino American between November 2022 and January 2023. Interviews were transcribed and coded using an iterative process. RESULTS: Most participants were familiar with genetic disease and believed that factors such as biology, as well as cultural factors such as upbringing and food, contributed to its development. The majority of participants had previously heard of genetic testing; however, most participants either did not know much or were only familiar with ancestry direct-to-consumer genetic testing (DTC-GT). Most participants had not heard of genetic counseling and those that had heard of genetic counseling before did not understand its purpose. Overall, most participants had a positive attitude toward genetic testing and counseling. Participants identified the benefits of these services including genetic disease prevention, management, and treatment. Participants stressed the importance of educating the Filipino community and shared their ideas for how to implement outreach efforts. DISCUSSION/CONCLUSION: This study found that Filipino Americans generally had a positive outlook on genetic testing and genetic counseling. We propose participant-generated ideas for outreach and education that may help inform future public health efforts that aim to educate this population about genetic disease, testing and counseling.

Rates and Classification of Variants of Uncertain Significance in Hereditary Disease Genetic Testing.

Importance: Variants of uncertain significance (VUSs) are rampant in clinical genetic testing, frustrating clinicians, patients, and laboratories because the uncertainty hinders diagnoses and clinical management. A comprehensive assessment of VUSs across many disease genes is needed to guide efforts to reduce uncertainty. Objective: To describe the sources, gene distribution, and population-level attributes of VUSs and to evaluate the impact of the different types of evidence used to reclassify them. Design, Setting, and Participants: This cohort study used germline DNA variant data from individuals referred by clinicians for diagnostic genetic testing for hereditary disorders. Participants included individuals for whom gene panel testing was conducted between September 9, 2014, and September 7, 2022. Data were analyzed from September 1, 2022, to April 1, 2023. Main Outcomes and Measures: The outcomes of interest were VUS rates (stratified by age; clinician-reported race, ethnicity, and ancestry groups; types of gene panels; and variant attributes), percentage of VUSs reclassified as benign or likely benign vs pathogenic or likely pathogenic, and enrichment of evidence types used for reclassifying VUSs. Results: The study cohort included 1 689 845 individuals ranging in age from 0 to 89 years at time of testing (median age, 50 years), with 1 203 210 (71.2%) female individuals. There were 39 150 Ashkenazi Jewish individuals (2.3%), 64 730 Asian individuals (3.8%), 126 739 Black individuals (7.5%), 5539 French Canadian individuals (0.3%), 169 714 Hispanic individuals (10.0%), 5058 Native American individuals (0.3%), 2696 Pacific Islander individuals (0.2%), 4842 Sephardic Jewish individuals (0.3%), and 974 383 White individuals (57.7%). Among all individuals tested, 692 227 (41.0%) had at least 1 VUS and 535 385 (31.7%) had only VUS results. The number of VUSs per individual increased as more genes were tested, and most VUSs were missense changes (86.6%). More VUSs were observed per sequenced gene in individuals who were not from a European White population, in middle-aged and older adults, and in individuals who underwent testing for disorders with incomplete penetrance. Of 37 699 unique VUSs that were reclassified, 30 239 (80.2%) were ultimately categorized as benign or likely benign. A mean (SD) of 30.7 (20.0) months elapsed for VUSs to be reclassified to benign or likely benign, and a mean (SD) of 22.4 (18.9) months elapsed for VUSs to be reclassified to pathogenic or likely pathogenic. Clinical evidence contributed most to reclassification. Conclusions and Relevance: This cohort study of approximately 1.6 million individuals highlighted the need for better methods for interpreting missense variants, increased availability of clinical and experimental evidence for variant classification, and more diverse representation of race, ethnicity, and ancestry groups in genomic databases. Data from this study could provide a sound basis for understanding the sources and resolution of VUSs and navigating appropriate next steps in patient care.

Recommendation of premarital genetic screening in the Syrian Jewish community based on mutation carrier frequencies within Syrian Jewish cohorts.

BACKGROUND: There is a paucity of information available regarding the carrier frequency for autosomal recessive pathogenic variants among Syrian Jews. This report provides data to support carrier screening for a group of autosomal recessive conditions among Syrian Jews based on the population frequency of 40 different pathogenic variants in a cohort of over 3800 individuals with Syrian Jewish ancestry. METHODS: High throughput PCR amplicon sequencing was used to genotype 40 disease-causing variants in 3840 and 5279 individuals of Syrian and Iranian Jewish ancestry, respectively. These data were compared with Ashkenazi Jewish carrier frequencies for the same variants, based on roughly 370,000 Ashkenazi Jewish individuals in the Dor Yeshorim database. RESULTS: Carrier screening identified pathogenic variants shared among Syrian, Iranian, and Ashkenazi Jewish groups. In addition, alleles unique to each group were identified. Importantly, 8.2% of 3401 individuals of mixed Syrian Jewish ancestry were carriers for at least one pathogenic variant. CONCLUSION: The findings of this study support the clinical usefulness of premarital genetic screening for individuals with Syrian Jewish ancestry to reduce the incidence of autosomal recessive disease among persons with Syrian Jewish heritage.

Autosomal recessive diseases among the Athabaskans of the southwestern United States: anthropological, medical, and scientific aspects.

The peopling of the Americas by Native Americans occurred in 4 waves of which the last was Nadene language speakers of whom Athabaskans are the largest group. As the Europeans were entering the Southwestern states of the USA, Athabaskan hunting-gathering tribes were migrating South from Canada along the Rocky Mountains and undergoing potential bottlenecks reflected in autosomal recessive diseases shared by Apaches and Navajos. About 300 years ago, the Navajo developing a sedentary culture learned from Pueblo Indians while the Apache remained hunter-gathers. Although most of the tribe was rounded up and forced to relocate to Bosque Redondo, the adult breeding population was large enough to prevent a genetic bottleneck. However, some Navajo underwent further population bottlenecks while hiding from the brutal US Army action (under Kit Carson's guidance). This led to an increased frequency of other autosomal recessive diseases. Recent advances in population genetics, pathophysiology of the diseases, and social/ethical issues concerning their study are reviewed.

The influence of social determinants of health on the genetic diagnostic odyssey: who remains undiagnosed, why, and to what effect?

Although Mendelian genetic disorders are individually rare, they are collectively more common and contribute disproportionately to pediatric morbidity and mortality. Remarkable advances in the past decade have led to identification of the precise genetic variants responsible for many of these conditions. Confirming the molecular diagnosis through genetic testing allows for individualized treatment plans in addition to ending the diagnostic odyssey, which not only halts further unnecessary testing but may also result in immense psychological benefit, leading to improved quality of life. However, ensuring equitable application of these advances in genomic technology has been challenging. Though prior studies have revealed disparities in testing for genetic predisposition to cancer in adults, little is known about the prevalence and nature of disparities in diagnostic testing in the pediatric rare disease population. While it seems logical that those with impaired access to healthcare would be less likely to receive the genetic testing needed to end their odyssey, few studies have addressed this question directly and the potential impact on health outcomes. This review synthesizes the available evidence regarding disparities in pediatric genetic diagnosis, defining the need for further, prospective studies with the ultimate goal of delivering precision medicine to all who stand to benefit. IMPACT: Social determinants of health are known to contribute to inequality in outcomes, though the impact on pediatric rare disease patients is not fully understood. Diagnostic genetic testing is a powerful tool, though it may not be available to all in need. This article represents the first effort, to our knowledge, to evaluate the existing literature regarding disparities in genetic testing for pediatric rare disease diagnosis and identify gaps in care.

Lessons learned from expanded reproductive carrier screening in self-reported Ashkenazi, Sephardi, and Mizrahi Jewish patients.

BACKGROUND: Next-generation sequencing (NGS)-based panels have gained traction as a strategy for reproductive carrier screening. Their value for screening Ashkenazi Jewish (AJ) individuals, who have benefited greatly from population-wide targeted testing, as well as Sephardi/Mizrahi Jewish (SMJ) individuals (an underserved population), has not been fully explored. METHODS: The clinical utilization by 6,805 self-reported Jewish individuals of an expanded NGS panel, along with several ancillary assays, was assessed retrospectively. Data were extracted for a subset of 96 diseases that, during the panel design phase, were classified as being AJ-, SMJ-, or pan-Jewish/pan-ethnic-relevant. RESULTS: 64.6% of individuals were identified as carriers of one or more of these 96 diseases. Over 80% of the reported variants would have been missed by following recommended AJ screening guidelines. 10.7% of variants reported for AJs were in "SMJ-relevant genes," and 31.2% reported for SMJs were in "AJ-relevant genes." Roughly 2.5% of individuals carried a novel, likely pathogenic variant. One in 16 linked cohort couples was identified as a carrier couple for at least one of these 96 diseases. CONCLUSION: For maximal carrier identification, this study supports using expanded NGS panels for individuals of all Jewish backgrounds. This approach can better empower at-risk couples for reproductive decision making.

Consanguinity and Inbreeding in Health and Disease in North African Populations.

North Africa is defined as the geographical region separated from the rest of the continent by the Sahara and from Europe by the Mediterranean Sea. The main demographic features of North African populations are their familial structure and high rates of familial and geographic endogamy, which have a proven impact on health, particularly the occurrence of genetic diseases, with a greater effect on the frequency and spectrum of the rarest forms of autosomal recessive genetic diseases. More than 500 different genetic diseases have been reported in this region, most of which are autosomal recessive. During the last few decades, there has been great interest in the molecular investigation of large consanguineous North African families. The development of local capacities has brought a substantial improvement in the molecular characterization of these diseases, but the genetic bases of half of them remain unknown. Diseases of known molecular etiology are characterized by their genetic and mutational heterogeneity, although some founder mutations are encountered relatively frequently. Some founder mutations are specific to a single country or a specific ethnic or geographic group, and others are shared by all North African countries or worldwide. The impact of consanguinity on common multifactorial diseases is less evident.

The Emergence of Genomic Research in Africa and New Frameworks for Equity in Biomedical Research.

Individuals with African ancestry have the greatest genomic diversity in the world, yet they have been underrepresented in genomic research. To advance our understanding of human biology and our ability to trace human history, we must include more samples from Africans in genomic research. Additionally, inclusion of more samples from participants of recent African descent is imperative to provide equitable health care as genomics is increasingly used for diagnosis, treatment, and to understand disease risk. The Human Heredity and Health in Africa initiative (H3Africa) seeks to expand the number of Africans included in genomic research and to do so by expanding the research capacity on the continent. In this article, we discuss how H3Africa is endeavoring to achieve these goals while promoting equitable research collaborations.

Short article: Sequence variations of PKHD1 underlie congenital hepatic fibrosis in a Chinese family.

OBJECTIVE: Congenital hepatic fibrosis (CHF) is a developmental disorder of the portobiliary system characterized by hepatic fibrosis, portal hypertension, and renal cystic disease. The aim of our study was to identify the disease-causing gene of a Chinese family with CHF. PATIENTS AND METHODS: Whole-exome sequencing was performed in the family with CHF and variants were confirmed by Sanger sequencing. Online bioinformatics tools were used to evaluate the pathogenicity of the missense variants. Liver specimens were reviewed to confirm the histopathological diagnosis. RESULTS: The compound heterozygous variants c.7994T>C, p.(Leu2665Pro) and c.8518C>T, p.(Arg2840Cys) in PKHD1 were identified in a Chinese family with CHF by whole-exome sequencing. Liver histomorphology was reviewed to confirm the diagnosis of CHF. CONCLUSION: We have identified variations in PKHD1 in a Chinese family with CHF. Our study extends the mutation spectrum of CHF and provides information for genetic counseling of patients' family members.

Inclusion and exclusion in the globalisation of genomics; the case of rare genetic disease in Brazil.

Within the context of a globalising agenda for genetic research where 'global health' is increasingly seen as necessarily informed by and having to account for genomics, the focus on rare genetic diseases is becoming prominent. Drawing from ethnographic research carried out separately by both authors in Brazil, this paper examines how an emerging focus on two different arenas of rare genetic disease, cancer genetics and a class of degenerative neurological diseases known as Ataxias, is subject to and a product of the dynamics of inclusion and exclusion as this concerns participation in research and access to health care. It examines how in these different cases 'rarenesss' has been diversely situated and differently politicised and how clinicians, patients and their families grapple with the slippery boundaries between research, rights to health and the limits of care, therapy or prevention. It illustrates how attention to rare genetic disease in Brazil emerges at the intersection of a particular history of genetic research and public health infrastructure, densely complicated feedback loops between clinical care and research, patient mobilisation around the 'judicialisation' of health and recent state legislation regarding rare disease in Brazil. It highlights the relevance of local configurations in the way rare genetic disease is being made relevant for and by different communities.

Carrier screening for single gene disorders.

Screening for genetic disorders began in 1963 with the initiation of newborn screening for phenylketonuria. Advances in molecular technology have made both newborn screening for newborns affected with serious disorders, and carrier screening of individuals at risk for offspring with genetic disorders, more complex and more widely available. Carrier screening today can be performed secondary to family history-based screening, ethnic-based screening, and expanded carrier screening (ECS). ECS is panel-based screening, which analyzes carrier status for hundreds of genetic disorders irrespective of patient race or ethnicity. In this article, we review the historical and current aspects of carrier screening for single gene disorders, including future research directions.

Modeled Fetal Risk of Genetic Diseases Identified by Expanded Carrier Screening.

IMPORTANCE: Screening for carrier status of a limited number of single-gene conditions is the current standard of prenatal care. Methods have become available allowing rapid expanded carrier screening for a substantial number of conditions. OBJECTIVES: To quantify the modeled risk of recessive conditions identifiable by an expanded carrier screening panel in individuals of diverse racial and ethnic backgrounds and to compare the results with those from current screening recommendations. DESIGN, SETTING, AND PARTICIPANTS: Retrospective modeling analysis of results between January 1, 2012, and July 15, 2015, from expanded carrier screening in reproductive-aged individuals without known indication for specific genetic testing, primarily from the United States. Tests were offered by clinicians providing reproductive care. EXPOSURES: Individuals were tested for carrier status for up to 94 severe or profound conditions. MAIN OUTCOMES AND MEASURES: Risk was defined as the probability that a hypothetical fetus created from a random pairing of individuals (within or across 15 self-reported racial/ethnic categories; there were 11 categories with >5000 samples) would be homozygous or compound heterozygous for 2 mutations presumed to cause severe or profound disease. Severe conditions were defined as those that if left untreated cause intellectual disability or a substantially shortened lifespan; profound conditions were those causing both. RESULTS: The study included 346,790 individuals. Among major US racial/ethnic categories, the calculated frequency of fetuses potentially affected by a profound or severe condition ranged from 94.5 per 100,000 (95% CI, 82.4-108.3 per 100,000) for Hispanic couples to 392.2 per 100,000 (95% CI, 366.3-420.2 per 100,000) for Ashkenazi Jewish couples. In most racial/ethnic categories, expanded carrier screening modeled more hypothetical fetuses at risk for severe or profound conditions than did screening based on current professional guidelines (Mann-Whitney P < .001). For Northern European couples, the 2 professional guidelines-based screening panels modeled 55.2 hypothetical fetuses affected per 100,000 (95% CI, 51.3-59.3 per 100,000) and the expanded carrier screening modeled 159.2 fetuses per 100,000 (95% CI, 150.4-168.6 per 100,000). Overall, relative to expanded carrier screening, guideline-based screening ranged from identification of 6% (95% CI, 4%-8%) of hypothetical fetuses affected for East Asian couples to 87% (95% CI, 84%-90%) for African or African American couples. CONCLUSIONS AND RELEVANCE: In a population of diverse races and ethnicities, expanded carrier screening may increase the detection of carrier status for a variety of potentially serious genetic conditions compared with current recommendations from professional societies. Prospective studies comparing current standard-of-care carrier screening with expanded carrier screening in at-risk populations are warranted before expanded screening is adopted.

Next-generation sequencing-based molecular diagnosis of 12 inherited retinal disease probands of Uyghur ethnicity.

Inherited retinal disease (IRD) is a category of genetic disorders affecting retina. Understanding the molecular basis of IRD is vital for clinical and genetic classification of patients. Uyghur people is an isolated ethnic group mainly residing in northwestern China with genetic admixture from Europeans and East Asians. The genetic etiology of IRD in this specific population still remains unknown. Here, by next-generation sequencing (NGS), we screened mutations in over 200 known retinal disease genes in a cohort of 12 unrelated Uyghur IRD probands. Out of the 12 probands, six are solved with high confidence, two with low confidence, while the remaining four are unsolved. We identified known disease-causing alleles in this cohort that suggest ancient Uyghur migration and also discovered eight novel disease-associated variants. Our results showed NGS-based mutation screening as a reliable approach for molecular diagnosis. In addition, this approach can also be applied to reveal the genetic history of a specific ethnic group.

Leveraging ancestry to improve causal variant identification in exome sequencing for monogenic disorders.

Recent breakthroughs in exome-sequencing technology have made possible the identification of many causal variants of monogenic disorders. Although extremely powerful when closely related individuals (eg, child and parents) are simultaneously sequenced, sequencing of a single case is often unsuccessful due to the large number of variants that need to be followed up for functional validation. Many approaches filter out common variants above a given frequency threshold (eg, 1%), and then prioritize the remaining variants according to their functional, structural and conservation properties. Here we present methods that leverage the genetic structure across different populations to improve filtering performance while accounting for the finite sample size of the reference panels. We show that leveraging genetic structure reduces the number of variants that need to be followed up by 16% in simulations and by up to 38% in empirical data of 20 exomes from individuals with monogenic disorders for which the causal variants are known.

The Israeli national population program of genetic carrier screening for reproductive purposes.

PURPOSE: The Israeli population genetic screening program for reproductive purposes, launched in January 2013, includes all known, nationally frequent severe diseases (carrier frequency 1:60 and/or disease frequency 1 in 15,000 live births). The carrier screening program is free of charge and offers testing for cystic fibrosis, fragile X syndrome, and spinal muscular atrophy for nearly the entire population, according to disease frequency among the different groups within the population. We report the results of the first year of the program. METHODS: Data on the tests performed over a 12-month period were collected from laboratories nationwide. RESULTS: More than 62,000 individuals were examined. The carrier frequency was within the expected range for most of the diseases. The few exceptions included lower carrier rates for cystic fibrosis among Muslim Arabs (1:236) and Druze (1:1,021) and Niemann-Pick type A among Muslim Arabs in a delineated region of Israel (1:229). CONCLUSION: The national population genetic carrier screening is aimed toward providing couples with knowledge of the existing options for the prevention of serious genetic conditions when it is relevant for them. It is still too early to determine whether this aim has been achieved.

CONSANGUINITY AND HOMOZYGOSITY AMONG TUNISIAN PATIENTS WITH AN AUTOSOMAL RECESSIVE DISORDER.

Consanguineous unions are a deeply rooted social practice among traditional societies. Despite their presumed social advantages, they can result in several health conditions. The aim of this study was: i) to compare consanguinity levels between Tunisian patients affected with autosomal recessive disorders (ARDs) and those with a chromosomal abnormality; and ii) to gain more insight into the mutational status of patients affected with ARDs. Data were collected from 290 files of patients affected by one of five ARDs confirmed by molecular analysis and 248 files of patients with confirmed Down syndrome. Information on the disease, mutation defining the disease, parents' relatedness and geographical origin was gathered. Consanguinity was found among 58% of the ARD patients and among 22% of Down syndrome patients, and a homozygous status was found in 90% of the patients born to related parents and in 70% of patients born to unrelated parents. Also, children from unrelated parents from the same geographical background were found to be more frequently affected by homozygous mutations than those from unrelated parents from different geographical backgrounds. The present study shows how marriage practices affect patterns of genetic variations and how they can lead to homogenization in the genetic pool.

Incidence and molecular basis of CD36 deficiency in Shanghai population.

BACKGROUND: CD36 is a multifunctional membrane receptor and is expressed in several cell lines. Individuals who lack platelet (PLT) CD36 are at risk for immunization against this antigen, leading to several clinical syndromes. This study aimed to investigate the frequency and molecular basis of CD36 deficiency in Shanghai. STUDY DESIGN AND METHODS: Whole blood samples were collected from healthy blood donors, and the PLTs and monocytes were analyzed using flow cytometry to determine CD36 deficiency type. After genomic DNA was extracted, Exons 3 to 14 of CD36 gene including a part of relevant flanking introns were amplified. Direct nucleotide sequencing and sequence alignment were performed. The samples that showed mutations were confirmed by clonal sequencing. RESULTS: Of the 1022 healthy blood donors analyzed, 22 individuals failed to express CD36 on PLTs; two of them expressed no CD36 on their monocytes either. These results demonstrated that the frequencies of Type I (lacking CD36 expression on PLTs and monocytes) and Type II (lacking CD36 expression on PLTs only) CD36 deficiency among the study population were 0.2 and 2.0%, respectively. Nucleotide sequencing analysis revealed nine different mutations including six mutations that were not yet reported. The most frequent mutations among the study population were 329-330delAC and 1228-1239delATTGTGCCTATT. CONCLUSION: The study findings have confirmed the fact that the frequency of CD36 deficiency in the Chinese population is slightly lower than that in other Asian countries. The identification of several new mutation types indicated the polymorphism of CD36 gene in the Shanghai population.