Kidney Function in People with Down Syndrome

We frequently see that the lab values of kidney function of people with Down syndrome (DS) we evaluate at our Center are mildly abnormal. The kidney function is slightly decreased compared to what is reported as "normal" for the population as a whole. This suggests that the kidneys of some people with DS do not cleanse their bodies of toxins as well as those of people without DS.

Two common labs that are measured through a blood test to assess kidney function are blood urea nitrogen (BUN) and creatinine. BUN measures the amount of nitrogen in the blood. This nitrogen comes from a waste product of the liver called urea. Creatinine is also a waste product. It is produced by the muscles. Both nitrogen and creatinine are filtered out by the kidneys. If the kidney function is decreased, the BUN and creatinine lab values go up. We frequently see mild elevations of one or both values. 

Based on our clinical experience, we suspect that kidney function is typically a little decreased in people with DS compared to those without DS but we have found very little in the medical literature to confirm our suspicion.

• A small study done in Japan  in children with DS found that the "kidney function in these children with DS was approximately 80% that of the healthy Japanese children, suggesting that children with DS have smaller kidneys or a lower number of glomeruli than children without DS." Glomeruli are one of the types of kidney cells, and they filter toxins out of the blood. The article cited previous studies that showed microscopic anatomical differences in the kidneys of children with DS.

• A review article  (that analyzed previously published studies) published by Emory University in 2004 reported that prior research had noted "decreased creatinine clearance" (decreased kidney function) in people with DS.

These studies support our sense that "typical" kidney function in people with DS is less than "typical" kidney function in those without DS. This may suggest a genetic difference due to DS. However, before accepting that there is a genetic inevitability, we suggest considering a few things. 

• We know from our experience that many people with DS do not drink enough fluids. Dehydration from not drinking enough fluids can contribute to kidney dysfunction. Therefore, even if it is "normal" or "typical" for someone with DS to have decreased kidney function, we still recommend optimizing kidney function by drinking plenty of fluids. How much is enough is up for some debate but consider drinking at least 1.5 to 2 liters of fluids (50-70 ounces) per day (in addition to what is available in the foods you eat). We have several resources in our Resource Library on hydration. 

• People with DS more commonly have poor bladder function. We have seen many people with DS who empty their bladder incompletely (urinary retention). This may be due to behavioral or habitual issues (e.g., holding urine for long periods of time even when the urge to urinate is present), anatomical obstructions or blockages, weak bladder muscle, or reduced nervous stimulation of the bladder muscle. Ultrasound evaluation of bladder function and kidney anatomy can evaluate for these causes and possibly lead to additional evaluation.

• Depending on the rest of the history, physical exam, and lab findings, additional evaluation for other causes may be indicated. For example, an elevated uric acid level is a common finding in people with DS. Elevated uric acid can cause gout (inflammation of joints due to uric acid crystals forming in the joint). Elevated uric acid can also cause kidney disease. On the other hand, decreased kidney function can cause an elevation of uric acid. So, an elevated uric acid, particularly in conjunction with abnormal kidney function, may require additional evaluation and a possible referral to a nephrologist (kidney specialist). 

Abnormal kidney function in people with DS may have both reversible and irreversible components. Further assessment of abnormal kidney function may reveal contributing causes that can be addressed/treated with appropriate interventions.