常染色体優性多発性嚢胞腎, autosomal dominant polycystic kidney disease
出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2013/05/24 02:29:49」(JST)
常染色体優性多発性嚢胞腎 | |
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分類及び外部参照情報 | |
常染色体優性多発性嚢胞腎
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ICD-10 | Q61. |
ICD-9 | 753.1 |
OMIM | 601313 173910 |
DiseasesDB | 10262 |
MedlinePlus | 000502 |
eMedicine | radio/68 |
MeSH | D016891 |
プロジェクト:病気/Portal:医学と医療 | |
テンプレートを表示 |
常染色体優性多発性嚢胞腎(Autosomal dominant polycystic kidney disease, ADPKD)は、腎疾患のひとつ。
多発性嚢胞腎の1タイプであり、ポリシスチン蛋白をコードする遺伝子の異常によって、腎臓に嚢胞が多発し、徐々に腎不全に至る疾患である。
尿細管・間質には炎症所見がみられ、実質正常細胞がアポトーシスを起こし線維化する。終末期には、嚢胞を線維の帯が囲むようになる。
目次
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詳細は「嚢胞性腎疾患」を参照
両側の腎臓において、細胞外マトリックス異常に起因して、既存の尿細管上皮の1%から発生した尿細管上皮が脱分化・増殖し、肉眼的に見える孤立球状嚢胞が年齢と共に増加。腎臓の皮質・髄質の「Bowman嚢から腎乳頭先端」のどこにでも多発する。嚢胞は径数mmを超えると、4分の3は尿細管から分離し、孤立嚢胞を形成する。上皮が腔内へ尿様の電解質液を分泌する(上皮の極性は保持される)ため、嚢胞は徐々に増大するとともに、腎は概形は保ちつつ両側性に肥大し、時に3kgにも達する。腎杯はおおきく歪む。この嚢胞は、周辺実質の機能障害を起こし、炎症細胞が浸潤し、正常細胞がアポトーシスするため、腎機能が低下する。
嚢胞の拡大につれて周囲動脈は伸展し障害され、糸球体濾過量(GFR)低下とレニン-アンジオテンシン系賦活によって、高血圧を起こす。20代 - 30代に発症(gene carrierは80歳までに100%が発症)する。終末期には、間質の線維化と細動脈硬化によって、半数は70歳までに腎正常実質はわずかになって末期腎不全に至る。このとき、腎臓はもとの数倍の大きさになる。
細胞外マトリックスからの(増殖・分化・輸送の)シグナルの細胞内への伝達に関与する「ポリシスチン蛋白」をコードするPKD1(頻度85%)・PKD2(頻度15%)などの遺伝子異常が基礎にあり、second hitで発症。
欠失、ミスセンス、フレームシフトはすべてポリシスチンの機能を下げる。
優性遺伝疾患としては、家族性高コレステロール血症に次いで多い。全世界に分布し、500人に1人が発症する。
発症を遅らせるなどの予防法は知られていない。
高血圧は必発症状で、腎肥大のために腹部膨満、易疲労、腰背部痛、便秘、食欲不振も起こりうる。
細胞外マトリックス遺伝子の異常であるため、全身の結合組織に異常が生じうる。肝臓・膵臓・脾臓・クモ膜などに嚢胞ができるほか、頭蓋内動脈瘤や僧帽弁逆流症を起こす。頭蓋内動脈瘤は高血圧と共に頭蓋内出血の危険因子となる。
肉眼的血尿・タンパク尿がみられる。嚢胞が感染を起こすと、頭痛・発熱を起こす。腹部超音波検査やCTにより、両側の腎臓に多発する嚢胞がみられる。PKD1、PKD2の遺伝子解析も可能だが、それ以外の未知の原因遺伝子もあることがわかっている。
特異的な治療法はない。高血圧や腎機能の低下に対し、対症療法を行う。腹部圧迫症状が著しい場合は、姑息的に嚢胞穿刺するが、感染には注意する。
発症すれば、いずれは末期腎不全に至り、人工透析を要する。頭蓋内動脈瘤の破裂は致命的になりうる。
内科、特に腎高血圧内科が専門科である。
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Polycystic Kidney Disease | |
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Classification and external resources | |
Polycystic kidneys |
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ICD-10 | Q61 |
ICD-9 | 753.1 |
OMIM | 601313 173910 |
DiseasesDB | 10262 |
MedlinePlus | 000502 |
eMedicine | radio/68 |
MeSH | D016891 |
Autosomal dominant polycystic kidney disease ("ADPKD", "autosomal dominant PKD" or "Adult-onset PKD") is an inherited systemic disorder that predominantly affects the kidneys, but may affect other organs including the liver, pancreas, brain, and arterial blood vessels. Approximately 50% of people with this disease will develop end stage kidney disease and require dialysis or kidney transplantation. Progression to end stage kidney disease usually happens in the 4th to 6th decades of life.[1] Autosomal dominant polycystic kidney disease occurs worldwide and affects about 1 in 400 to 1 in 1000 people.[2][3]
Defects in two genes are thought to be responsible for ADPKD. In 85% of patients, ADPKD is caused by mutations in the gene PKD1 on chromosome 16 (TRPP1); in 15% of patients mutations in PKD2 (TRPP2) are causative.[1]
Autosomal recessive polycystic kidney disease is a distinct disease that also leads to cysts in the kidneys and liver, typically presents in childhood, only affects about 1 in 20,000 people[4] and has different causes and prognosis.
Contents
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Recent studies in fundamental cell biology of cilia and flagella using experimental model organisms such as the round worm Caenorhabditis elegans and the mouse Mus musculus have shed light on how PKD develops in human patients.[5]
All cilia and flagella are constructed and maintained by the process of intraflagellar transport, a cellular function that is also essential for the insertion of proteins at specific sites along cilia and flagella membranes. These inserted membrane proteins can initiate environmental sensing and intracellular signaling pathways. They play a special role in the cilia of renal epithelial cells, and are thought to be critical for normal renal cell development and function and are sorted out and localized to the cilia of renal epithelial cells by the aforementioned intraflagellar transport mechanism. Ciliated epithelial cells line the lumen of the urinary collecting ducts and sense the flow of urine. Failure in flow-sensing signaling results in programmed cell death (apoptosis) of these renal epithelial cells, producing the characteristic multiple cysts of PKD. PKD may result from mutations of signaling and environmental sensing proteins, or failure in intraflagellar transport.[6]
Two PKD genes, PKD1 and PKD2, encode membrane proteins that localize to a non-motile cilium on the renal tube cell. Polycystin-2 encoded by PKD2 gene is a calcium channel that allows extracellular calcium ions to enter the cell. Polycystin-1, encoded by PKD1 gene, is thought to be associated with polycystin-2 protein and regulates polycystin-2's channel activity. The calcium ions are important cellular messengers, which trigger complicated biochemical pathways that lead to quiescence and differentiation. Malfunctions of polycystin-1 or polycystin-2 proteins, defects in the assembly of the cilium on the renal tube cell, failures in targeting these two proteins to the cilium, and deregulations of calcium signaling all likely cause the occurrence of PKD.
As stated above, defects in two genes are thought to be responsible for ADPKD. In 85% of patients, ADPKD is caused by mutations in the gene PKD1 on chromosome 16 (TRPP1); in 15% of patients mutations in PKD2 (TRPP2) are causative.[1][7]
The two hit hypothesis (aka Knudson hypothesis ) is often used to explain the manifestation of polycystic kidney disease later in life even though the mutation is present at birth. This term is borrowed from cancer research stating that both copies of the gene present in the genome have to be "silenced" before cancer manifests itself (in Knudson's case the silenced gene was Rb1). In ADPKD the original "hit" is congenital (in either the PKD1 or PKD2 genes) and the subsequent "hit" occurs later in life as the cells grow and divide. The two hit hypothesis as it relates to PKD was originally proposed by Reeders in 1992.[8] Support for this hypothesis comes from the fact that ARPKD patients develop disease at birth, and somatic mutations in the "normal" copy of PKD1 or PKD2 have been found in cyst-lining epithelia
Recent findings in genetic research have suggested that a large number of genetic disorders, both genetic syndromes and genetic diseases, that were not previously identified in the medical literature as related, may be, in fact, highly related in the genetypical root cause of the widely-varying, phenotypically-observed disorders. Thus, PKD is a ciliopathy. Other known ciliopathies include primary ciliary dyskinesia, Bardet-Biedl syndrome, polycystic liver disease, nephronophthisis, Alstrom syndrome, Meckel-Gruber syndrome, and some forms of retinal degeneration.[9]
A definite diagnosis of ADPKD relies on imaging or molecular genetic testing. The sensitivity of testing is nearly 100% for all patients with ADPKD who are age 30 years or older and for younger patients with PKD1 mutations; these criteria are only 67% sensitive for patients with PKD2 mutations who are younger than age 30 years. Large echogenic kidneys without distinct macroscopic cysts in an infant/child at 50% risk for ADPKD are diagnostic. In the absence of a family history of ADPKD, the presence of bilateral renal enlargement and cysts, with or without the presence of hepatic cysts, and the absence of other manifestations suggestive of a different renal cystic disease provide presumptive, but not definite, evidence for the diagnosis.
Molecular genetic testing by linkage analysis or direct mutation screening is available clinically; however, genetic heterogeneity is a significant complication to molecular genetic testing. Sometimes a relatively large number of affected family members need to be tested in order to establish which one of the two possible genes is responsible within each family. The large size and complexity of PKD1 and PKD2 genes, as well as marked allelic heterogeneity, present obstacles to molecular testing by direct DNA analysis. In the research setting, mutation detection rates of 50-75% have been obtained for PKD1 and ~75% for PKD2. Clinical testing of the PKD1 and PKD2 genes by direct sequence analysis is now available, with a detection rate for disease-causing mutations of 50-70%.
Genetic counseling may be helpful for families at risk for polycystic kidney disease.
Although a cure for PKD is not available, treatment can ease the symptoms and prolong life.
Despite significant research, prognosis of this disease has changed little over time. It is suggested that avoidance of caffeine may prevent cyst formation. Although not well-proven, treatment of hypertension and a low protein diet may slow progression of the disease.
Between PKD1 and PKD2, the former has the worse prognosis.
Adult polycystic kidney.
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国試過去問 | 「102I012」 |
リンク元 | 「100Cases 10」「常染色体優性多発性嚢胞腎」「多発性嚢胞腎」「腎嚢胞」「autosomal dominant polycystic kidney」 |
関連記事 | 「ADP」 |
※国試ナビ4※ [102I011]←[国試_102]→[102I013]
常染色体優性多発性嚢胞腎 : 約 133,000 件 常染色体優性嚢胞腎 : 56 件
高血圧:腎機能が正常な患者のほとんどに存在。40年間程度持続する。高熱圧の存在によりほとんど全員が末期腎不全に至る。
嚢胞疾患の合併:肝臓、膵臓、脾臓、甲状腺、精巣上体
(参考2)
死因は心臓による物が最多である:心臓病(36%)、感染症(24%)、神経学的なイベント(12%)。剖検では心肥大が89%の患者に見られ、冠動脈疾患が81%に見られた。神経学的な死亡(neurologic deaths)では頭蓋内動脈瘤破裂が主であり(6%)、頭蓋内出血が5%であった。
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