Polycystic kidney disease | |
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Other names | Kidney - polycystic [1] |
Severely affected polycystic kidneys removed at time of transplantation | |
Specialty | Nephrology |
Symptoms | Abdominal pain [1] |
Types | ADPKD [2] and ARPKD [3] |
Diagnostic method | MRI, CT scan, Ultrasound [1] |
Treatment | Antihypertensives, Life style management [4] |
Polycystic kidney disease (PKD or PCKD, also known as polycystic kidney syndrome) is a genetic disorder [5] [6] in which the renal tubules become structurally abnormal, resulting in the development and growth of multiple cysts within the kidney. [7] These cysts may begin to develop in utero, in infancy, in childhood, or in adulthood. [8] Cysts are non-functioning tubules filled with fluid pumped into them, which range in size from microscopic to enormous, crushing adjacent normal tubules and eventually rendering them non-functional as well.
PKD is caused by abnormal genes that produce a specific abnormal protein; this protein has an adverse effect on tubule development. PKD is a general term for two types, each having their own pathology and genetic cause: autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD). The abnormal gene exists in all cells in the body; as a result, cysts may occur in the liver, seminal vesicles, and pancreas. This genetic defect can also cause aortic root aneurysms, and aneurysms in the circle of Willis cerebral arteries, which if they rupture, can cause a subarachnoid hemorrhage.
Diagnosis may be suspected from one, some, or all of the following: new onset flank pain or red urine; a positive family history; palpation of enlarged kidneys on physical exam; an incidental finding on abdominal sonogram; or an incidental finding of abnormal kidney function on routine lab work (BUN, serum creatinine, or eGFR). Definitive diagnosis is made by abdominal CT exam.
Complications include hypertension due to the activation of the renin–angiotensin–aldosterone system (RAAS), frequent cyst infections, urinary bleeding, and declining renal function. Hypertension is treated with angiotensin converting enzyme inhibitors (ACEIs) or angiotensin receptor blockers (ARBs). Infections are treated with antibiotics. Declining renal function is treated with renal replacement therapy (RRT): dialysis and/or transplantation. Management from the time of the suspected or definitive diagnosis is by an appropriately trained doctor.
Signs and symptoms include high blood pressure, headaches, abdominal pain, blood in the urine, and excessive urination. [1] Other symptoms include pain in the back, and cyst formation (renal and other organs). [9]
PKD is caused by abnormal genes which produce a specific abnormal protein which has an adverse effect on tubule development. PKD is a general term for two types, each having their own pathology and genetic cause: autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD). [10] [11]
Autosomal dominant polycystic kidney disease (ADPKD) is the most common of all the inherited cystic kidney diseases [12] [13] [14] with an incidence of 1:500 live births. [12] [14] Studies show that 10% of end-stage kidney disease (ESKD) patients being treated with dialysis in Europe and the U.S. were initially diagnosed and treated for ADPKD. [12] [11]
Genetic mutations in any of the three genes PKD1, PKD2, and PKD3 have similar phenotypical presentations. [15]
Autosomal recessive polycystic kidney disease (ARPKD) (OMIM #263200) is the less common of the two types of PKD, with an incidence of 1:20,000 live births and is typically identified in the first few weeks after birth. Unfortunately, the kidneys are often underdeveloped, resulting in a 30% death rate in newborns with ARPKD. PKHD1 is involved. [12] [11]
Both autosomal dominant and autosomal recessive polycystic kidney disease cyst formation are tied to abnormal cilia-mediated signaling. The polycystin-1 and polycystin-2 proteins appear to be involved in both autosomal dominant and recessive polycystic kidney disease due to defects in both proteins. [21] Both proteins have communication with calcium channel proteins, and cause reduction in resting (intracellular) calcium and endoplasmic reticulum storage of calcium. [22]
The disease is characterized by a 'second hit' phenomenon, in which a mutated dominant allele is inherited from a parent, with cyst formation occurring only after the normal, wild-type gene sustains a subsequent second genetic 'hit', resulting in renal tubular cyst formation and disease progression. [21]
PKD results from defects in the primary cilium, an immotile, hair-like cellular organelle present on the surface of most cells in the body, anchored in the cell body by the basal body. [21] In the kidney, primary cilia have been found to be present on most cells of the nephron, projecting from the apical surface of the renal epithelium into the tubule lumen. The cilia were believed to bend in the urine flow, leading to changes in signalling, however this has since been shown to be an experimental error (the bending of cilia was an artifact of focal plane compensation, and also the actual effect on micturition by severe hypertension and cardiac arrest) and that bending of cilia does not contribute to alterations in Ca flux. While it is not known how defects in the primary cilium lead to cyst development, it is thought to possibly be related to disruption of one of the many signaling pathways regulated by the primary cilium, including intracellular calcium, Wnt/β-catenin, cyclic adenosine monophosphate (cAMP), or planar cell polarity (PCP). Function of the primary cilium is impaired, resulting in disruption of a number of intracellular signaling cascades which produce differentiation of cystic epithelium, increased cell division, increased apoptosis, and loss of resorptive capacity. [11] [21]
Polycystic kidney disease can be ascertained via a CT scan of abdomen, as well as an MRI and ultrasound of the same area. [23] A physical exam/test can reveal enlarged liver, heart murmurs and elevated blood pressure. [1]
Most cases progress to bilateral disease in adulthood. [12]
In 2018, Jynarque (Tolvaptan) was introduced [24] as the first FDA-approved treatment for PKD. In a recent long-term study, patients using Tolvaptan had a 6.4% higher kidney function after 5 years compared to standard of care. [25] In 2019, a team of researchers at UCSB found that a ketogenic diet might be able to halt, or even reverse progression in mice, [26] and the results of a first human case series study are showing potential benefit. [27] The results of a 3-month randomized, prospective dietary intervention clinical trial are pending. [28] In addition, recent research indicates that mild to moderate calorie restriction or time-restricted feeding [29] slow the progression of autosomal dominant polycystic kidney disease (ADPKD) in mice. [30] [31] Patient communities have been combining both ketogenic diets [32] and time-restricted feeding with a low-oxalate diet to prevent the formation of stones [33] and early reports show an average of 17% increase in kidney function after approximately one year on a ketogenic, time-restricted dietary regimen. [34] If and when the disease progresses enough in a given case, the nephrologist or other practitioner and the patient will have to decide what form of renal replacement therapy will be used to treat end-stage kidney disease (kidney failure, typically stage 4 or 5 of chronic kidney disease). [35]
That will either be some form of dialysis, which can be done at least two different ways at varying frequencies and durations (whether it is done at home or in the clinic depends on the method used and the patient's stability and training) and eventually, if they are eligible because of the nature and severity of their condition and if a suitable match can be found, unilateral or bilateral kidney transplantation. [35]
A Cochrane Review study of autosomal dominant polycystic kidney disease made note of the fact that it is important at all times, while avoiding antibiotic resistance, to control infections of the cysts in the kidneys, and if affected, the liver, when needed for a certain duration to combat infection, by using, "bacteriostatic and bacteriocidal drugs". [11] [35]
ADPKD individuals might have a normal life; conversely, ARPKD can cause kidney dysfunction and can lead to kidney failure by the age of 40–60. ADPKD1 and ADPKD2 are very different, in that ADPKD2 is much milder. [36]
Currently, there are no therapies proven effective to prevent the progression of ADPKD. [37]
PKD is one of the most common hereditary diseases in the United States, affecting more than 600,000 people. It is the cause of nearly 10% of all end-stage renal disease. It equally affects men, women, and all races. [38] PKD occurs in some animals as well as humans. [39] [40]
Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common, life-threatening inherited human disorders and the most common hereditary kidney disease. It is associated with large interfamilial and intrafamilial variability, which can be explained to a large extent by its genetic heterogeneity and modifier genes. It is also the most common of the inherited cystic kidney diseases — a group of disorders with related but distinct pathogenesis, characterized by the development of renal cysts and various extrarenal manifestations, which in case of ADPKD include cysts in other organs, such as the liver, seminal vesicles, pancreas, and arachnoid membrane, as well as other abnormalities, such as intracranial aneurysms and dolichoectasias, aortic root dilatation and aneurysms, mitral valve prolapse, and abdominal wall hernias. Over 50% of patients with ADPKD eventually develop end stage kidney disease and require dialysis or kidney transplantation. ADPKD is estimated to affect at least one in every 1000 individuals worldwide, making this disease the most common inherited kidney disorder with a diagnosed prevalence of 1:2000 and incidence of 1:3000-1:8000 in a global scale.
Kidney disease, or renal disease, technically referred to as nephropathy, is damage to or disease of a kidney. Nephritis is an inflammatory kidney disease and has several types according to the location of the inflammation. Inflammation can be diagnosed by blood tests. Nephrosis is non-inflammatory kidney disease. Nephritis and nephrosis can give rise to nephritic syndrome and nephrotic syndrome respectively. Kidney disease usually causes a loss of kidney function to some degree and can result in kidney failure, the complete loss of kidney function. Kidney failure is known as the end-stage of kidney disease, where dialysis or a kidney transplant is the only treatment option.
Alport syndrome is a genetic disorder affecting around 1 in 5,000–10,000 children, characterized by glomerulonephritis, end-stage kidney disease, and hearing loss. Alport syndrome can also affect the eyes, though the changes do not usually affect vision, except when changes to the lens occur in later life. Blood in urine is universal. Proteinuria is a feature as kidney disease progresses.
Gitelman syndrome (GS) is an autosomal recessive kidney tubule disorder characterized by low blood levels of potassium and magnesium, decreased excretion of calcium in the urine, and elevated blood pH. It is the most frequent hereditary salt-losing tubulopathy. Gitelman syndrome is caused by disease-causing variants on both alleles of the SLC12A3 gene. The SLC12A3 gene encodes the thiazide-sensitive sodium-chloride cotransporter, which can be found in the distal convoluted tubule of the kidney.
Secondary hypertension is a type of hypertension which has a specific and identifiable underlying primary cause. It is much less common than essential hypertension, affecting only 5-10% of hypertensive patients. It has many different causes including obstructive sleep apnea, kidney disease, endocrine diseases, and tumors. The cause of secondary hypertension varies significantly with age. It also can be a side effect of many medications.
Cystic kidney disease refers to a wide range of hereditary, developmental, and acquired conditions and with the inclusion of neoplasms with cystic changes, over 40 classifications and subtypes have been identified. Depending on the disease classification, the presentation may be at birth, or much later into adult life. Cystic disease may involve one or both kidneys and may, or may not, occur in the presence of other anomalies. A higher incidence is found in males and prevalence increases with age. Renal cysts have been reported in more than 50% of patients over the age of 50. Typically, cysts grow up to 2.88 mm annually and may cause related pain and/or hemorrhage.
Medullary cystic kidney disease (MCKD) is an autosomal dominant kidney disorder characterized by tubulointerstitial sclerosis leading to end-stage renal disease. Because the presence of cysts is neither an early nor a typical diagnostic feature of the disease, and because at least four different gene mutations may give rise to the condition, the name autosomal dominant tubulointerstitial kidney disease (ADTKD) has been proposed, to be appended with the underlying genetic variant for a particular individual. Importantly, if cysts are found in the medullary collecting ducts they can result in a shrunken kidney, unlike that of polycystic kidney disease. There are two known forms of medullary cystic kidney disease, mucin-1 kidney disease 1 (MKD1) and mucin-2 kidney disease/uromodulin kidney disease (MKD2). A third form of the disease occurs due to mutations in the gene encoding renin (ADTKD-REN), and has formerly been known as familial juvenile hyperuricemic nephropathy type 2.
Polycystic liver disease (PLD) usually describes the presence of multiple cysts scattered throughout normal liver tissue. PLD is commonly seen in association with autosomal-dominant polycystic kidney disease, with a prevalence of 1 in 400 to 1000, and accounts for 8–10% of all cases of end-stage renal disease. The much rarer autosomal-dominant polycystic liver disease will progress without any kidney involvement.
Fibrocystin is a large, receptor-like protein that is thought to be involved in the tubulogenesis and/or maintenance of duct-lumen architecture of epithelium. FPC associates with the primary cilia of epithelial cells and co-localizes with the Pkd2 gene product polycystin-2 (PC2), suggesting that these two proteins may function in a common molecular pathway.
Nephronophthisis is a genetic disorder of the kidneys which affects children. It is classified as a medullary cystic kidney disease. The disorder is inherited in an autosomal recessive fashion and, although rare, is the most common genetic cause of childhood kidney failure. It is a form of ciliopathy. Its incidence has been estimated to be 0.9 cases per million people in the United States, and 1 in 50,000 births in Canada.
Polycystin 1 (PC1) is a protein that in humans is encoded by the PKD1 gene. Mutations of PKD1 are associated with most cases of autosomal dominant polycystic kidney disease, a severe hereditary disorder of the kidneys characterised by the development of renal cysts and severe kidney dysfunction.
Polycystin-2(PC2) is a protein that in humans is encoded by the PKD2 gene.
Conorenal syndrome, is a collection of medical conditions that seem to have a common genetic cause.
A ciliopathy is any genetic disorder that affects the cellular cilia or the cilia anchoring structures, the basal bodies, or ciliary function. Primary cilia are important in guiding the process of development, so abnormal ciliary function while an embryo is developing can lead to a set of malformations that can occur regardless of the particular genetic problem. The similarity of the clinical features of these developmental disorders means that they form a recognizable cluster of syndromes, loosely attributed to abnormal ciliary function and hence called ciliopathies. Regardless of the actual genetic cause, it is clustering of a set of characteristic physiological features which define whether a syndrome is a ciliopathy.
Autosomal recessive polycystic kidney disease (ARPKD) is the recessive form of polycystic kidney disease. It is associated with a group of congenital fibrocystic syndromes. Mutations in the PKHD1 cause ARPKD.
Lixivaptan (VPA-985) is an orally-active, non-peptide, selective vasopressin 2 receptor antagonist being developed as an investigational drug by Palladio Biosciences, Inc. (Palladio), a subsidiary of Centessa Pharmaceuticals plc. As of December 2021, lixivaptan is in Phase III clinical development for the treatment of Autosomal dominant polycystic kidney disease (ADPKD), the most common form of polycystic kidney disease. The U.S. Food and Drug Administration (FDA) has granted orphan drug designation to lixivaptan for the treatment of ADPKD.
Glomerulocystic kidney disease (GCKD) is a cystic disorder of the kidneys. GCKD involves cystic dilation of Bowman's capsule. It can occur with or without congenital abnormality.
The Polycystin Cation Channel (PCC) Family consists of several transporters ranging in size from 500 to over 4000 amino acyl residues (aas) in length and exhibiting between 5 and 18 transmembrane segments (TMSs). This family is a constituent of the Voltage-Gated Ion Channel (VIC) Superfamily. These transporters generally catalyze the export of cations. A representative list of proteins belonging to the PCC family can be found in the Transporter Classification Database.
Polycystic kidney disease 3 (autosomal dominant) is a protein that in humans is encoded by the PKD3 gene.
Shrawan Kumar, is an Indian-American geneticist, working in the fields of molecular and population genetics. He contributed to the discovery of two genes related to Branchio-oto-renal syndrome (BOR) and Autosomal Dominant Polycystic Kidney Disease (ADPKD2).