Holoprosencephaly (HPE) is a cephalic disorder in which the prosencephalon fails to develop into two hemispheres, typically occurring between the 18th and 28th day of gestation. Normally, the forebrain is formed and the face begins to develop in the fifth and sixth weeks of human pregnancy. The condition also occurs in other species.
Arachnodactyly is a medical condition that is characterized by fingers and toes that are abnormally long and slender, in comparison to the palm of the hand and arch of the foot. In some cases, the thumbs of an individual with the condition are pulled inwards towards the palm. This condition is present at birth.
Norrie disease is a rare disease and genetic disorder that primarily affects the eyes and almost always leads to blindness. It is caused by mutations in the Norrin cystine knot growth factor (NDP) gene, which is located on the X chromosome. In addition to the congenital ocular symptoms, the majority of patients experience a progressive hearing loss starting mostly in their 2nd decade of life, and some may have learning difficulties among other additional characteristics.
DiGeorge syndrome, also known as 22q11.2 deletion syndrome, is a syndrome caused by a microdeletion on the long arm of chromosome 22. While the symptoms can vary, they often include congenital heart problems, specific facial features, frequent infections, developmental delay, learning problems and cleft palate. Associated conditions include kidney problems, schizophrenia, hearing loss and autoimmune disorders such as rheumatoid arthritis or Graves' disease.
Mowat–Wilson syndrome is a rare genetic disorder that was clinically delineated by David R. Mowat and Meredith J. Wilson in 1998.
22q13 deletion syndrome, also known as Phelan–McDermid syndrome (PMS), is a genetic disorder caused by deletions or rearrangements on the q terminal end of chromosome 22. Any abnormal genetic variation in the q13 region that presents with significant manifestations (phenotype) typical of a terminal deletion may be diagnosed as 22q13 deletion syndrome. There is disagreement among researchers as to the exact definition of 22q13 deletion syndrome. The Developmental Synaptopathies Consortium defines PMS as being caused by SHANK3 mutations, a definition that appears to exclude terminal deletions. The requirement to include SHANK3 in the definition is supported by many but not by those who first described 22q13 deletion syndrome.
Meckel-Gruber syndrome is a rare, lethal ciliopathic genetic disorder, characterized by renal cystic dysplasia, central nervous system malformations, polydactyly (postaxial), hepatic developmental defects, and pulmonary hypoplasia due to oligohydramnios. Meckel–Gruber syndrome is named for Johann Meckel and Georg Gruber.
Confined placental mosaicism (CPM) represents a discrepancy between the chromosomal makeup of the cells in the placenta and the cells in the fetus. CPM was first described by Kalousek and Dill in 1983. CPM is diagnosed when some trisomic cells are detected on chorionic villus sampling and only normal cells are found on a subsequent prenatal test, such as amniocentesis or fetal blood sampling. In theory, CPM is when the trisomic cells are found only in the placenta. CPM is detected in approximately 1-2% of ongoing pregnancies that are studied by chorionic villus sampling (CVS) at 10 to 12 weeks of pregnancy. Chorionic villus sampling is a prenatal procedure which involves a placental biopsy. Most commonly when CPM is found it represents a trisomic cell line in the placenta and a normal diploid chromosome complement in the baby. However, the fetus is involved in about 10% of cases.
Trisomy 16 is a chromosomal abnormality in which there are 3 copies of chromosome 16 rather than two. It is the most common trisomy leading to miscarriage and the second most common chromosomal cause of it, closely following X-chromosome monosomy. About 6% of miscarriages have trisomy 16. Those mostly occur between 8 and 15 weeks after the last menstrual period.
18p- is a genetic condition caused by a deletion of all or part of the short arm of chromosome 18. It occurs in about 1 of every 50,000 births.
Silver–Russell syndrome (SRS), also called Silver–Russell dwarfism, is a rare congenital growth disorder. In the United States it is usually referred to as Russell–Silver syndrome (RSS), and Silver–Russell syndrome elsewhere. It is one of 200 types of dwarfism and one of five types of primordial dwarfism.
46,XX/46,XY is an exceptionally rare chimeric genetic condition characterized by the presence of some cells that express a 46,XX karyotype and some cells that express a 46,XY karyotype in a single human being. The cause of the condition lies in utero with the aggregation of two distinct blastocysts or zygotes into a single embryo, which subsequently leads to the development of a single individual with two distinct cell lines, instead of a pair of fraternal twins. 46,XX/46,XY chimeras are the result of the merging of two non-identical twins. This is not to be confused with mosaicism or hybridism, neither of which are chimeric conditions. Since individuals with the condition have two cell lines of the opposite sex, it can also be considered an intersex condition.
Young–Madders syndrome, alternatively known as Pseudotrisomy 13 syndrome or holoprosencephaly–polydactyly syndrome, is a genetic disorder resulting from defective and duplicated chromosomes which result in holoprosencephaly, polydactyly, facial malformations and mental retardation, with a significant variance in the severity of symptoms being seen across known cases. Many cases often suffer with several other genetic disorders, and some have presented with hypoplasia, cleft lip, cardiac lesions and other heart defects. In one case in 1991 and another in 2000 the condition was found in siblings who were the product of incest. Many cases are diagnosed prenatally and often in siblings. Cases are almost fatal in the prenatal stage with babies being stillborn.
Ring chromosome 15 is a condition that arises when chromosome 15 fuses to form a ring chromosome. Usually, ring chromosome 15 forms due to the modification or deletion of genetic information on chromosome 15 in the preliminary stages of embryonic development, but it can rarely also be inherited.
Noninvasive prenatal testing is a method used to determine the risk for the fetus being born with certain chromosomal abnormalities, such as trisomy 21, trisomy 18 and trisomy 13. This testing analyzes small DNA fragments that circulate in the blood of a pregnant woman. Unlike most DNA found in the nucleus of a cell, these fragments are not found within the cells, instead they are free-floating, and so are called cell free fetal DNA (cffDNA). These fragments usually contain less than 200 DNA building blocks and arise when cells die, and their contents, including DNA, are released into the bloodstream. cffDNA derives from placental cells and is usually identical to fetal DNA. Analysis of cffDNA from placenta provides the opportunity for early detection of certain chromosomal abnormalities without harming the fetus.
Weyer's ulnar ray/oligodactyly syndrome is a rare multi-systemic genetic disorder which is characterized by ectrodactyly, ulnar, radial, or fibular ray deficit, and heart, single central incisor, splenic, and renal abnormalities. Cleft lip/palate and hypoplasia of the mandibles have also been observed. It is thought to be inherited in an autosomal recessive pattern. It was first discovered in 1957 by Weyers et al. Only four families worldwide are known to be affected by the disorder.
Combarros-Calleja-Leno syndrome is a very rare genetic disorder which is characterized by a combination of ataxia indistinguishable from Friedreich's ataxia and congenital glaucoma. Additional findings include pes cavus and generalized areflexia. It has been described in 7 members from a consanguineous Spanish family.
Palmoplantar keratoderma with deafness, also known as Palmoplantar keratoderma-deafness syndrome is a rare genetic disorder which is characterized by either focal or diffuse early-onset palmoplantar keratoderma and sensorineural deafness. Transmission is autosomal dominant with incomplete penetrance.
Hall-Riggs syndrome is a rare genetic disorder that causes neurological issues and birth defects. People with Hall-Riggs syndrome usually have skeletal dysplasia, facial deformities, and intellectual disabilities. Only 8 cases from 2 families worldwide have been described in medical literature. It is an autosomal recessive genetic disorder, meaning both parents must carry the gene in order for their offspring to be affected.
