Editing Polymicrogyria (section)

== Syndromes ==
{{Original research|section|date=March 2017}}

Significant technological advances have been made within the past few decades that have allowed more extensive studies to be made regarding syndromes from conditions such as polymicrogyria. Research, imaging, and analysis has shown that distribution of polymicrogyria does not always appear to be random, which revealed different types polymicrogyria. A summary of clinical manifestations of each syndrome can be found below, in the section labelled "[[#Signs and symptoms|Clinical presentation]]".{{citation needed|date=January 2021}}

The main patterns of polymicrogyria are: perisylvian (61%), generalised (13%), frontal (5%), and parasagittal parieto-occipital (3%) and 11% is associated with [[gray matter heterotopia]] ([[grey matter]] is located in the [[white matter]] instead of usual location in the [[cerebral cortex]]).<ref name="pmid20403963">{{cite journal | vauthors = Leventer RJ, Jansen A, Pilz DT, Stoodley N, Marini C, Dubeau F, Malone J, Mitchell LA, Mandelstam S, Scheffer IE, Berkovic SF, Andermann F, Andermann E, Guerrini R, Dobyns WB | title = Clinical and imaging heterogeneity of polymicrogyria: a study of 328 patients | journal = Brain: A Journal of Neurology | volume = 133 | issue = Pt 5 | pages = 1415–27 | date = May 2010 | pmid = 20403963 | pmc = 2859156 | doi = 10.1093/brain/awq078 | url = }}</ref>

=== Bilateral frontal polymicrogyria (BFP) ===
{{Infobox medical condition (new)
| name          = Polymicrogyria
| synonyms      = PMG
| image         = Polymicrogyria.jpg
| caption       = Bilateral perisylvian polymicrogyria
}}

BFP appears to be a symmetrical polymicrogyria that extends anteriorly from the frontal poles to the posterior precentral gyrus, and inferiorly to the frontal operculum. Patients who had polymicrogyria distribution similar to this also experienced similar symptoms including delayed motor and language developments, spastic hemiparesis or quadriparesis, and forms of mild intellectual disability.{{citation needed|date=January 2021}}

=== Bilateral frontoparietal polymicrogyria (BFPP) ===
{{Main|Bilateral frontoparietal polymicrogyria}}

BFPP was one of the first discovered forms of polymicrogyria to have a gene identified linking to the syndromes caused. This gene is called [[GPR56]]. Symmetrical distribution is also evident in this form, but more distinctly, patients with BFPP were found to have [[atrophy]] of the [[cerebellum]] and [[brain stem]], as well as bilateral [[white matter]] abnormalities. BFPP is characterized by [[esotropia]], global development delay, pyramidal signs, cerebral signs, and seizures. Esotropia is also known as dysconjugate gaze, and is a common feature of severe static [[encephalopathy]]. This differentiates BFPP from the other bilateral polymicrogyria syndromes.{{citation needed|date=January 2021}}

=== Bilateral perisylvian polymicrogyria (BPP) ===
BPP is similar to the other types of polymicrogyria in that it is usually symmetrical, but BPP can vary among patients. BPP is characterized by its location; the cerebral cortex deep in the sylvian fissures is thickened and abnormally infolded, as well as the sylvian fissures extending more posteriorly up to the parietal lobes and more vertically oriented.<ref name="Nathan Source">{{cite journal|last1=Jansen|first1=A.|last2=Andermann|first2=E.|title=Genetics of the polymicrogyria syndromes|journal=Journal of Medical Genetics|pages=369–378|doi=10.1136/jmg.2004.023952|date=1 May 2005|pmid=15863665|volume=42|issue=5|pmc=1736054}}</ref> BPP has been classified into a grading system consisting of four different grades that describe the variations in severity:{{citation needed|date=January 2021}}

{{ordered list|type=none
  | Grade 1: Perisylvian polymicrogyria extends to either one or both poles
  | Grade 2: Perisylvian polymicrogyria extends past the perisylvian region, but not to either of the poles
  | Grade 3: Perisylvian polymicrogyria is contained in the perisylvian region only
  | Grade 4: Perisylvian polymicrogyria is contained in the posterior perisylvian region only
}}

The grades move from most severe (Grade 1) to least severe (Grade 4). Although BFPP was the first form of polymicrogyria to be discovered, BPP was the first form to be described and is also the most common form of polymicrogyria. The clinical characterizations of BPP "include pseudobulbar palsy with diplegia of the facial, pharyngeal and masticory muscles (facio-pharyngo-glosso-masticatory paresis), pyramidal signs, and seizures."<ref name="Nathan Source" /> These can result in drooling, feeding issues, restricted tongue movement, and [[dysarthria]].<ref name="Nathan Source" /> Disorders in language development have also been associated with BPP, but the extent of language disorder depends on the severity of cortical damage. Patients who have BPP can also have pyramidal signs that vary in severity, and can be either unilateral or bilateral.<ref name="Nathan Source" />

The sodium channel SCN3A has been implicated in BPP.<ref name="Oral Motor Development 2018">{{cite journal |last1=Smith |first1=RS |last2=Kenny |first2=CJ |last3=Ganesh |first3=V |last4=Jang |first4=A |last5=Borges-Monroy |first5=R |last6=Partlow |first6=JN |last7=Hill |first7=RS |last8=Shin |first8=T |last9=Chen |first9=AY |last10=Doan |first10=RN |last11=Anttonen |first11=AK |last12=Ignatius |first12=J |last13=Medne |first13=L |last14=Bönnemann |first14=CG |last15=Hecht |first15=JL |last16=Salonen |first16=O |last17=Barkovich |first17=AJ |last18=Poduri |first18=A |last19=Wilke |first19=M |last20=de Wit |first20=MCY |last21=Mancini |first21=GMS |last22=Sztriha |first22=L |last23=Im |first23=K |last24=Amrom |first24=D |last25=Andermann |first25=E |last26=Paetau |first26=R |last27=Lehesjoki |first27=AE |last28=Walsh |first28=CA |last29=Lehtinen |first29=MK |title=Sodium Channel SCN3A (Na<sub>V</sub>1.3) Regulation of Human Cerebral Cortical Folding and Oral Motor Development. |journal=Neuron |date=5 September 2018 |volume=99 |issue=5 |pages=905–913.e7 |doi=10.1016/j.neuron.2018.07.052 |pmid=30146301|pmc=6226006 }}</ref>

=== Bilateral parasagittal parieto-occipital polymicrogyria (BPOP) ===
BPOP is located in the parasagittal and mesial regions of the parieto-occipital cortex. This form has been associated with IQ scores that range from average intelligence to mild intellectual disability, seizures, and cognitive slowing. The age of seizure onset has been found to occur anywhere from 20 months to 15 years, and in most cases the seizures were intractable (meaning hard to control).<ref name="Nathan Source" />

=== Bilateral generalised polymicrogyria (BGP) ===
BGP is most severe in the perisylvian regions, but occurs in a generalised distribution. Associated factors include a reduced volume of white matter and [[ventriculomegaly]]. BGP tends to show excessively folded and fused gyri of an abnormally thin cerebral cortex, and an absence of the normal six-layered structure. The abnormally thin cortex is a key factor that distinguishes this form of polymicrogyria from the others, which are characterized by an abnormally thick cortex. Most of the patients have cognitive and motor delay, spastic hemi- or quadriparesis, and seizures in varying degrees. The seizures also vary at age of onset, type, and severity. There have been pseudobulbar signs reported with BGP, which are also seen in patients with BPP. This association leads to the belief that there is overlap between patients with BGP and patients with grade 1 BPP.<ref name="Nathan Source" />

=== Unilateral polymicrogyria ===
The region in which unilateral polymicrogyria occurs has been generalized into different cortical areas. Features associated with this form of polymicrogyria are similar to the other forms and include spastic hemiparesis, intellectual disability in variable degrees, and seizures. The features depend on the exact area and extent to which polymicrogyria has affected the cortex. Patients who have unilateral polymicrogyria have been reported to also have electrical status epilepticus during sleep (EPES), and all had seizures.<ref name="Nathan Source" />