Newborn screening for lysosomal diseases: current status and potential interface with population medical genetics in Latin America

Abstract

The aim of newborn screening (NBS) programs is to detect a condition in a presymptomatic baby and provide management measures which could significantly improve the natural history of the disease. NBS programs for metabolic diseases were first introduced in North America and Europe and in the 1960s for phenylketonuria, expanded a few years later to include congenital hypothyroidism, and have been growing steadily in terms of number of conditions tested for and number of countries and births covered. Lysosomal storage diseases (LSDs) are a group of around 50 genetic conditions in which a defect in a lysosomal function occurs. LSDs are progressive conditions, being usually asymptomatic at birth, but with clinical features becoming apparent in childhood, with severe manifestations in most instances, high morbidity and shortened life span. Although individually rare, the prevalence of LSDs is significant when the group is considered as a whole (around 1:4,000-1:9,000 live births). Several management techniques, including bone marrow transplantation, enzyme replacement therapy, substrate inhibition therapy, pharmacological chaperones and many other approaches are transforming the LSDs into treatable conditions. However, lack of awareness and lack of access to tests cause a significant delay between onset of symptoms and diagnosis. Several lines of evidence showing that the earlier introduction of therapy may provide a better outcome, are bringing support to the idea of including LSDs in NBS programs. Due to advances in technology, high-throughput multiplex methods are now available for mass screening of several LSDs. Pilot projects were already developed in many countries for some LSDs, with interesting results. Although some NBS in Latin America has been carried out since the 1970s, it has so far been incorporated as a public health program in only a few countries in the region. It will probably take many years before NBS is implemented in most Latin American countries with a comprehensive coverage in terms of number of diseases and number of births. Population medical genetics is the area of medical genetics that aims at the study and medical care of the population, and not of the family, which is the case for clinical or medical genetics itself. It combines different aspects of genetics: clinical genetics; human population genetics, which investigates populations according to micro-evolutionary parameters; epidemiological genetics, traditionally involved in the study of common chronic diseases of polygenic etiology, except for Mendelian diseases; and sanitary or community genetics, which stands at the interface with public health, giving support to preventive health measures. Taking into account that several LSDs were identified in a higher frequency in selected areas and/or populations, the population medical genetics approach could help to introduce the NBS for LSDs in the region, with identification of areas with higher risk for selected diseases and design of customized screening program to address specific needs. As an example of the potential of this approach, a pilot program of NBS for MPS VI was implemented in a community from North East Brazil where 13 cases of MPS VI were identified in an area with 50,000 inhabitants. This program, which will enable not only identification and early treatment of affected newborns but also carrier detection, and which would allow genetic counseling for at-risk couples, could be an alternative model for a customized NBS of LSDs to be carried out in selected regions.