Chromosomal Anomaly Defects

Patau syndrome is a syndrome caused by a chromosomal abnormality, in which some or all of the cells of the body contain extra genetic material from chromosome 13.

Patau syndrome can be caused by each cell containing a full extra copy of chromosome 13 (trisomy 13), extra partial copy of the chromosome, or having two different lines of cells—one healthy and one containing an extra copy of the chromosome (mosaic Patau syndrome).

Full trisomy 13 is caused by nondisjunction of chromosomes during meiosis.

Mosaic Patau syndrome is caused by nondisjunction during mitosis.

The risk of Patau syndrome in the offspring increases with maternal age at pregnancy, with about 31 years being the average.

Patau syndrome disrupts normal development, causing multiple and complex organ defects.

Patau syndrome affects somewhere between 1 in 10,000 and 1 in 21,700 live births.

Other nondisjunction conditions similar to Patau syndrome include Down syndrome and Edwards syndrome.

Full trisomy 13 is when each cell contains a full extra copy of chromosome 13, while mosaic Patau syndrome is when there are two different lines of cells, one healthy with the correct number of chromosomes 13 and one that contains an extra copy of the chromosome.

Patau syndrome can be caused by each cell containing extra genetic material from chromosome 13, either in the form of a full extra copy of the chromosome or an extra partial copy, or due to the presence of two different lines of cells, one healthy and one containing an extra copy of the chromosome (mosaic Patau syndrome).

Patau syndrome results from trisomy 13, where each cell in the body has three copies of chromosome 13 instead of the usual two.

It can also occur as a result of a translocation, where part of chromosome 13 becomes attached to another chromosome before or at conception.

Most cases are not inherited but occur as random events during the formation of reproductive cells.

The chances of having another trisomy 13 affected child is less than 1%.

Diagnosis is usually based on clinical findings, although fetal chromosome testing will show trisomy 13.

The quad screen does not reliably screen for this disorder due to variability of results seen in fetuses with Patau.

Medical management of children with Trisomy 13 is planned on a case-by-case basis and depends on the individual circumstances of the patient.

Approximately 90% of infants with Patau syndrome die within the first year of life, and those who survive are typically severely disabled with intellectual disability, seizures, and psychomotor issues.

The chromosomal nature of the disease was ascertained in 1960 by Dr. Klaus Patau and Dr. Eeva Therman.

During 2008–09, there were 172 diagnoses of Patau syndrome, with 91% of diagnoses made prenatally.

Trisomy 18, also known as Edwards syndrome, is a genetic disorder caused by the presence of a third copy of all or part of chromosome 18.

Common features of Trisomy 18 include small size at birth, heart defects, small head, small jaw, clenched fists with overlapping fingers, and severe intellectual disability.

Most cases of Trisomy 18 occur due to problems during the formation of the reproductive cells or during early development.

Trisomy 18 can be confirmed by amniocentesis, which can be preceded by suspicion from an ultrasound during pregnancy.

Survival beyond a year of life for individuals with Trisomy 18 is around 5–10%.

Trisomy 18 is named after English geneticist John Hilton Edwards, who first described the syndrome in 1960.

After having one child with the condition, the risk of having a second is typically around one percent.

Trisomy 18 occurs in around 1 in 5,000 live births.

Trisomy 18 is the second-most common condition due to a third chromosome at birth, after Down syndrome.

The chance of Trisomy 18 occurring increases with the mother's age.

Edwards' syndrome presents with various characteristics, including kidney malformations, heart defects, omphalocele, intellectual disability, and physical malformations such as microcephaly and clubfoot.

The syndrome is caused by the presence of an extra copy of genetic material on the 18th chromosome, either in whole (trisomy 18) or in part (due to translocations), with effects varying depending on the extent of the extra copy, genetic history, and chance.

Trisomy 18 occurs due to meiotic nondisjunction, resulting in the presence of three copies of chromosome 18, and is more prevalent in female offspring.

Diagnosis of trisomy 18 can be confirmed by ultrasound, chorionic villus sampling (CVS), or amniocentesis, with specific biomarkers such as PAPP-A, AFP, uE3, and free beta HCG being indicative of the condition.

The prognosis for trisomy 18 is generally poor, with about 95% of affected pregnancies not resulting in live births, and half of live infants not surviving beyond the first week of life.

Trisomy 18 has an estimated median lifespan of five to 15 days, with 8-12% of infants surviving longer than 1 year and only 1% living to age 10, although survival rates may be higher with surgical intervention.

Trisomy 18 occurs in about 1 in 5,000 live births, but more pregnancies are affected as the majority of those diagnosed with the condition prenatally do not survive to birth, and the risk increases with maternal age.

Trisomy 18 was first identified by John Hilton Edwards in 1960, and later confirmed to be caused by an extra chromosome 18, with the average maternal age for conceiving a child with this disorder being 32.5.

The syndrome is also associated with in utero cardiac anomalies, central nervous system anomalies, and the presence of choroid plexus cysts, which may indicate its presence.

Notable causes of death in trisomy 18 include apnea and heart abnormalities, making it impossible to predict an exact prognosis during pregnancy or the neonatal period.

Polyploidy is a condition in which the cells of an organism have more than two pairs of homologous chromosomes. It is especially common in plants and is less common in animals. Most eukaryotes are diploid, but some organisms are polyploid.

Haploid cells have one set of chromosomes, while diploid cells have two complete sets of chromosomes, one from each parent.

Polyploidy may occur due to abnormal cell division during mitosis, the failure of chromosomes to separate during meiosis, or from the fertilization of an egg by more than one sperm. It can also be induced in plants and cell cultures by certain chemicals.

Plants and multicellular algae have life cycles with two alternating multicellular generations. The gametophyte generation is haploid and produces gametes by mitosis, while the sporophyte generation is diploid and produces spores by meiosis.

Polyploidy can be induced by certain chemicals such as colchicine and oryzalin, which can result in chromosome doubling.

Polyploidy can result from abnormal cell division during mitosis or from the failure of chromosomes to separate during meiosis, leading to an abnormal chromosome complement.

Polyploidy is widespread among mammals and occurs in organs such as the brain, liver, heart, and bone marrow. It is also found in somatic cells of animals such as goldfish, salmon, and salamanders, as well as in ferns and flowering plants, including agricultural crops like wheat, Brassica, and sugarcane.

Polyploid types are labeled according to the number of chromosome sets in the nucleus, such as haploid (1x), diploid (2x), tetraploid (4x), hexaploid (6x), and octaploid (8x).

Autopolyploids are polyploids with multiple chromosome sets derived from a single taxon. Autotriploidy can result in seedlessness in plants and is utilized in salmon and trout farming to induce sterility. Autopolyploids possess at least three homologous chromosome sets, leading to high rates of multivalent pairing during meiosis and a decrease in fertility.

Allopolyploids have chromosomes derived from two or more diverged taxa and can occur through the fusion of unreduced gametes from different taxa or after hybridization of diploid F1 hybrids.

Autopolyploids may arise from spontaneous, somatic genome doubling, and can also be induced artificially using methods such as protoplast fusion or treatment with colchicine.

Polyploidy is a significant phenomenon with implications for genetics, evolution, and agriculture, and is found in a diverse range of organisms.

Hybridization followed by genome duplication may be a common path to allopolyploidy because F1 hybrids between taxa often have relatively high rates of unreduced gamete formation, leading to abnormal pairing between homoeologous chromosomes or nondisjunction during meiosis. Allopolyploidy can restore normal, bivalent meiotic pairing by providing each homoeologous chromosome with its own homologue, resulting in rapid restoration of bivalent pairing and disomic inheritance following allopolyploidization.

Multivalent pairing is common in many recently formed allopolyploids, indicating that meiotic stabilization occurs gradually through selection, and pairing between homoeologous chromosomes is rare in established allopolyploids.

Established allopolyploids may benefit from fixed heterozygosity of homoeologous alleles, which can have beneficial heterotic effects, either in terms of fitness in natural contexts or desirable traits in agricultural contexts, potentially explaining the prevalence of allopolyploidy among crop species.

Examples of allopolyploids in crop species include bread wheat and Triticale with six chromosome sets, while examples of allotetraploids include cotton, peanut, and quinoa with multiple origins. In Brassicaceous crops, the Triangle of U describes the relationships between diploid Brassicas and allotetraploids derived from hybridization among the diploid species.

Aneuploidy refers to a numerical change in part of the chromosome set, whereas polyploidy refers to a numerical change in the whole set of chromosomes. Organisms in which a particular chromosome, or chromosome segment, is under- or over-represented are said to be aneuploid.

Endopolyploidy refers to polyploidy occurring in some tissues of animals that are otherwise diploid. For example, human muscle tissues exhibit endopolyploidy. Additionally, prokaryotes, such as the large bacterium Epulopiscium fishelsoni, may also be polyploid.

The Triangle of U describes the relationships between the three common diploid Brassicas and three allotetraploids derived from hybridization among the diploid species. It illustrates the complex patterns of allopolyploid evolution in Brassicaceous crops.

Complex patterns of allopolyploid evolution have been observed in animals, as in the frog genus Xenopus.