Editorial: Rare diseases research and diagnosis in low- and middle-income countries

component, and more than 6,000 conditions have been linked to a known molecular cause. In the last 15 years, the adoption of human genomic sequencing has enabled the more efficient and accurate diagnosis and research of rare genetic disorders. Genomic sequencing has become a first-tier diagnostic test for many patients with congenital syndromes and suspected genetic disorders in high-income countries, as well as an effective method for the study of undiagnosed and novel genetic disorders in the research arena. The implementation of massive parallel sequencing technologies, in the form of candidate gene panels, exome, or whole genome sequencing, has dramatically changed the diagnosis and research of rare diseases in high-income countries. In contrast, the reality in low-and middle-income countries (LMICs) is strikingly different, where disparities in access to these technologies exist. The high cost of genomic sequencing and other genetic analysis technologies remains a limiting factor for the implementation of these methods for diagnosis and research of rare diseases in resource limited settings.The study of rare genetic diseases in LMICs remains significantly underrepresented compared to large-scale genomic studies conducted in high-income countries. Despite some being carried out under resource-constrained conditions, these efforts often receive limited visibility in the scientific literature. As a result, there is a disproportionate lack of data from LMICs, which restricts the global understanding of the genetic and phenotypic Other reviews included in this Special Topic cover the advantages and challenges of incorporating CNV analyses from exome data to improve the yield of exome sequencing in resource-constrained settings (Louw et al.) where the availability and affordability of whole genome sequencing is still lagging. Additionally, Giugliani and colleagues review the current landscape and challenges of newborn screening programs in Latin America.Despite demonstrated to be a highly-effective public health strategy, newborn screening is still not broadly implemented in Latin America and other LMICs in the world. Early and accurate detection of rare diseases is fundamental to reduce mortality and morbidity associated with RDs and ensure quality of life for patients.In summary, the wide variety of papers published as part of this Special Topic highlight that even in resource constrained settings, molecular genetic testing, including genomic sequencing, for rare disorders is extremely valuable for diagnosis, research, management and counseling of patients and families living with RDs. Efforts should continue and increase to make these technologies more broadly available and affordable to be successfully implemented in LMICs. This collection adds to the rapidly expanding knowledge coming from historically underrepresented populations and countries and should be welcomed by all those in the field who wish to see genetic and genomic data from global populations represented in international genomic databases.