Wikipedia:Osmosis/Multicystic dysplastic kidney



Author: Tanner Marshall, MS

Editor: Rishi Desai, MD, MPH

Multicystic dysplastic kidney or MCDK is a congenital disease where one or both kidneys don’t form quite right, specifically causing them to not drain urine properly, which results in urine building up in the kidneys and forming multiple fluid-filled sacs called cysts. Alright so during fetal development, first off you’ve got this structure called the mesonephric duct which is involved in development of urinary and reproductive organs, and during the 5th week of gestation, a little guy called the ureteric bud starts pushing its way into another structure called the metanephric blastema, and together, these two little embryologic structures go on to develop into a kidney. At about the 7th week, nephrogenesis, or formation of the kidneys, starts under the influence of that ureteric bud.

By about 20 weeks, the ureteric bud has formed the ureters, the renal calyces, collecting ducts, and collecting tubules, while the metanephric blastema develops into the nephron itself, which includes the epithelial cells and the podocytes of Bowman’s capsule.

In the third trimester and throughout infancy, the kidneys continue to grow and mature.

Although not completely known, it’s thought that MCDK is a result of some sort of abnormal induction of the metanephric blastema by the ureteric bud. This failure might be the fault of the mesonephric duct not forming right, or the ureteric bud not forming right, or both.

Regardless of the cause of failure, the ureteric bud is supposed to go on to form the ureters as well as the rest of the tubules that branch out to collect urine.

So as blood starts coming in to be filtered, and urine starts getting produced, a failure to properly develop into these urine-collecting tubules means that the urine has nowhere to go, and so it builds up in the kidneys and forms these fluid-filled cysts that are composed of abnormal connective tissue—especially cartilage—that actually replaces normal kidney tissue and decreases the kidney’s ability to function. Most cases are actually unilateral, meaning they affect only one kidney, although sometimes it might be bilateral, where both are affected.

MCDK is usually a sporadic condition that happens during development, and does not follow a clear inheritance pattern; which is an important distinction from polycystic kidney disease, a similar cystic kidney disease that’s familial, meaning inherited and in this case it’s typically passed through autosomal dominant inheritance.

Having said that, there are some genetic syndromes, like papillorenal syndrome, that have been associated with MCDK, as well as some genes that may play a role like EYA1, SIX1, and the PAX2 gene. Certain prescription drugs taken for maternal hypertension like ACE inhibitors, as well as illicit drugs like cocaine have also been implicated as potentially causing MCDK in the developing fetus.

If only one kidney’s been affected and the other’s functioning normally, the remaining kidney might be able to preserve overall kidney function. If it’s bilateral and mild, the newborn may need dialysis and/or a kidney transplant, but newborns with severe bilateral MCDK usually don’t survive. Alright, so as a quick recap, multicystic dysplastic kidney is a type of non-inherited congenital kidney disease where the ureteric bud fails to develop properly, resulting in a buildup of urine, and formation of cysts.

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