Table 4.

Major remaining research problems and questions.

1	International standard for (gene-specific) DBP and reference method for the measurement of DBP
2	Validation of measurement of free 25OHD and its potential clinical value in comparison with total 25OHD
3	Validation of measurement or calculation of free 1,25(OH)2D and its potential physiologic and clinical implications
4	Understanding of the environmental drive (and health implications) for the world-wide gene polymorphism of DBP/GC
5	Full understanding of the implications of actin-DBP binding in health and diseases
6	Understanding of the role of DBP in inflammation
7	Role of megalin and DBP-25OHD uptake, if any, in non-renal cells