Diagnosis
Prenatal diagnosis
PKS is commonly diagnosed by detecting its causative sSMC as defined by identifying the overexpression of its genetic material. This method has detected the sSMC and therefore diagnosed a fetus as having PKS based on genomic analyses of fetal skin fibroblasts, placenta chorionic villi, cells isolated from the amniotic fluid, fibroblasts isolated from the fetuss umbilical cord, and cells isolated from the fetuss umbilical cord blood. PKS can also be diagnose using fetal ultasound imaging methods. Ultrasound imaging in PKS commonly find fetuses that are too large for their gestational age, contain polyhydramnios (excess amniotic fluid in their amniotic sacs), and have rhizomelic limbs (shortening of the proximal part of the limbs). Less commonly, the imaging evidences diaphragmatic hernias and/or various other major PKS structural malformations. In most cases, however, the ultrasound findings are not diagnostic of PKS. Furthermore, ultrasound diagnoses is best applied in the second or third pregnancy trimester when structural anomalies are more clearly defined and detectable.Because the prenatal diagnosis of PKS using the methods just cited is difficult, often indecisive, and/or best employed later in a womans pregnancy, prenatal cell-free DNA screening (cfDNA screening), also known as noninvasive prenatal screening, has been used to diagnose PKS. This method can diagnose PKS in 10 week and older fetuses. In cfDNA screening, DNA from a mothers blood is extracted and screened for the presence of specific chromosome abnormalities such as those associated with the Down syndrome, Patau syndrome (also termed trisomy 13), and Edwards syndrome (also termed trisomy 18).
Recent studies in two individuals with PKS found their sSMCs consisted specifically of genetic material located in a stretch of chromosome 12 s p arm starting at its band 11 and running to its end. This area, called the PKS critical region, contains three genes, ING4, CHD4, and MFAP5 (also termed the MAGP2 gene), which are candidates for contributing to the development of the syndrome.One suggested mechanism for the development of the sSMC in PKS involves three sequential events: 1) chromosome 12 suffers a nondisjunction, i.e. a failure of its homologous chromosomes or sister chromatids to separate properly during the second meiosis cell division that forms maternal eggs; 2) while most of the eggs with this nondisjunction die, a rare egg with the nondisjunction acquires a second structural aberration, isochromosome formation, that results in the creation of an extra chromosome consisting of copies of two or four p arms but no q arms of chromosome 12, i.e. the sSMC; and 3) the sSMC-containing egg, after being fertilized by a genetically normal sperm, develops into an offspring containing copies of this sSMC in some but not all cells, tissues, and/or organs consequently have some but not all of the defects associated with PKS. This mechanism applies only to female parents who are by far the most common originators of the sSMC in PKS. The mechanism explaining the few cases in which male parents form a sperm containing this sSMC has not yet been clearly formulated.