Editing Potter sequence (section)

==Types==
Since its initial characterization, Potter sequence has been defined into five distinct subclassifications. There are those in the medical and research fields that use the term Potter sequence to specifically refer to only cases of BRA, while other groups use the term to loosely refer to all instances of [[oligohydramnios]] and [[anhydramnios]] regardless of the specific cause. The assignment of nomenclature to the various causes (types) was employed in order to help clarify these discrepancies, but these subclassifications and nomenclature system have not caught on in the medical and research communities.{{citation needed|date=April 2021}}

{| class="wikitable"
|-
! Type
! [[OMIM]]
! Description
|-
| Classic form
| n/a
| This term is traditionally used when the infant has bilateral renal agenesis (BRA), meaning that kidneys do not develop (malformation of the [[ureteric bud]]). True BRA also presents with bilateral agenesis of the [[ureters]]. After the creation of the nomenclature system for this sequence, BRA was recognized as possibly being an extreme variation of Potter sequence II. However, some clinicians and researchers still use the term ''classic Potter sequence'' so as to emphasize that they are specifically referring to cases of BRA and not another form.
|-
| Type I
| {{OMIM|263200||none}}
| Type I is due to [[autosomal recessive polycystic kidney disease]] (ARPKD), which occurs at a frequency of approximately one in 16,000 infants.  The kidneys of the fetus/neonate will be enlarged, have many small cysts filled with fluid, and will fail to produce an adequate volume of fetal urine. The liver and pancreas of the fetus may also show [[fibrosis]] and/or a cystic change.
|-
| Type II
| {{OMIM|191830||none}}
| Type II is usually due to [[renal agenesis]],<ref name="pmid4744207">{{cite journal |vauthors=Buchta RM, Viseskul C, Gilbert EF, Sarto GE, Opitz JM |title=Familial bilateral renal agenesis and hereditary renal adysplasia |journal=Z Kinderheilkd |volume=115 |issue=2 |pages=111–29 |date=August 1973 |pmid=4744207 |doi= 10.1007/BF00440537|s2cid=1156279 }}</ref> which can also fall under the category known as ''hereditary urogenital adysplasia'' or ''hereditary renal adysplasia'' (HRA). This is characterized by the complete agenesis or absence of one kidney and the remaining solitary kidney being small and malformed. Bilateral renal agenesis is believed to be the most extreme phenotypic variation of HRA. However, BRA is often referred to as ''classic Potter sequence'', as it was this particular [[phenotype]] of neonates and fetuses that Potter originally reported in her 1946 manuscripts when characterizing this birth defect.
|-
| Type III
| {{OMIM|173900||none}}
| Type III is due to [[autosomal dominant polycystic kidney disease]] (ADPKD) linked to mutations in the genes [[PKD1]] and [[PKD2]]. While ADPKD is considered to be an adult-onset polycystic kidney disease, it can also present in the fetus and neonate in rare cases. Like ARPKD, ADPKD can also present with hepatic cysts and an enlarged spleen. An increased prevalence of vascular disease is also observed in these cases of ADPKD.
|-
| Type IV
| n/a
| Type IV occurs when a longstanding obstruction in either the kidney or [[ureter]] leads to cystic kidneys or [[hydronephrosis]]. This can be due to chance, environment, or genetics. While these types of obstructions occur frequently in fetuses, they rarely tend to lead to fetal demise.
|-
| Others
| {{OMIM|143400||none}}
| Often cystic kidneys that do not fall under the classification of being polycystic will be termed as being ''multicystic renal dysplasia'' (MRD). Recently many cases of MRD have been linked to the mutations in the gene [[TBX18]], however, this new possible genetic cause has not been assigned a Potter sequence nomenclature number.<br />Another cause of Potter sequence (oligohydramnios or anhydramnios—little or no amniotic fluid) can be the rupturing of the [[amniotic sac]]s that contain the amniotic fluid of the fetus. This can happen spontaneously, by chance, environment, maternal [[Physical trauma|trauma]] and, in rare cases, maternal genetics.
|}