52 Kidney volume was found to be proportional to nephron number in this study. Mutations in other genes such as Imx-1, Eya-1, Six1, Sall1, and tcf2 also result in a reduced nephron number, small kidney size, and disorganized renal tissue, in addition to other extrarenal manifestations.53 OTHER CLINICAL CORRELATES OF NEPHRON NUMBER Except for rough estimates of the nephron number by renal MRI or kidney biopsy, an accurate count can only be done post mortem.15,43,54 In humans, thus far, LBW and prematurity are Inhibitors,research,lifescience,medical the strongest clinical correlates of low nephron number. In animals, however, low nephron
number has been reported in the absence of LBW, and, conversely, not all LBW animals have reduced nephron numbers; therefore birth weight alone may not be a universal surrogate marker for nephron number.55,56 Several additional clinical surrogates for Inhibitors,research,lifescience,medical nephron number have been examined (Figure 1), which, although not absolute, may also serve to increase awareness of the possibility of low nephron number, with the attendant risks for hypertension and renal disease, and may therefore impact
on optimization of other risk factors. Anthropomorphic Factors Females are estimated to have 12% fewer glomeruli than males.43,57,58 Increasing age is associated with a predicted Inhibitors,research,lifescience,medical reduction of 3,676 glomeruli per kidney per year after age 18.15,43 Adult height has been found to correlate positively with nephron number, with an estimated increase of 28,000 glomeruli per centimeter increase in height, and height was found to contribute to two-thirds of the variance in glomerular number.15,43,58 Birth weight Inhibitors,research,lifescience,medical tends to
be associated with subsequent height and therefore may be a confounder in this relationship, but adult height is much more readily available than birth weight in clinical practice and therefore useful.59 Glomerular Volume Although nephron number does not increase after birth, the kidney matches its filtration capacity to the body’s demands by increasing the glomerular size through hypertrophy.5,11,12,57,58 As such, mean glomerular volumes have consistently Inhibitors,research,lifescience,medical been found to correlate inversely with glomerular number and Selleck INCB28060 directly with current body size.43 Keller et al. reported a 133% higher mean glomerular volume and a 46.6% reduction in glomerular number in hypertensive subjects, compared to controls.6 Lower nephron nearly number, black race, hypertension, and body size all correlate with an increase in individual glomerular volume within a single kidney.14,17,43 Larger glomeruli therefore suggest a lower nephron number, although in African-Americans glomerular volume appears to be globally increased but still in inverse proportion to nephron number, suggesting additional factors contribute to glomerular size in this population.9 Kidney Mass Kidney weight can only be measured ex vivo, but from autopsy studies, nephron number correlates directly with kidney weight in adults and children.15,52 Zhang et al.