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Lissencephaly is a set of rare brain disorders where the whole or parts of the surface of the brain appear smooth. It is caused by defective neuronal migration during the 12th to 24th weeks of gestation resulting in a lack of development of brain folds (gyri) and grooves (sulci). It is a form of cephalic disorder. Terms such as agyria and pachygyria are used to describe the appearance of the surface of the brain.
Cri du chat syndrome is a rare genetic disorder due to a partial chromosome deletion on chromosome 5. Its name is a French term referring to the characteristic cat-like cry of affected children. It was first described by Jérôme Lejeune in 1963. The condition affects an estimated 1 in 50,000 live births across all ethnicities and is more common in females by a 4:3 ratio.
Jacobsen syndrome is a rare chromosomal disorder resulting from deletion of genes from chromosome 11 that includes band 11q24.1. It is a congenital disorder. Since the deletion takes place on the q arm of chromosome 11, it is also called 11q terminal deletion disorder. The deletion may range from 5 million to 16 million deleted DNA base pairs. The severity of symptoms depends on the number of deletions; the more deletions there are, the more severe the symptoms are likely to be.
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.
Larsen syndrome (LS) is a congenital disorder discovered in 1950 by Larsen and associates when they observed dislocation of the large joints and face anomalies in six of their patients. Patients with Larsen syndrome normally present with a variety of symptoms, including congenital anterior dislocation of the knees, dislocation of the hips and elbows, flattened facial appearance, prominent foreheads, and depressed nasal bridges. Larsen syndrome can also cause a variety of cardiovascular and orthopedic abnormalities. This rare disorder is caused by a genetic defect in the gene encoding filamin B, a cytoplasmic protein that is important in regulating the structure and activity of the cytoskeleton. The gene that influences the emergence of Larsen syndrome is found in chromosome region, 3p21.1-14.1, a region containing human type VII collagen gene. Larsen syndrome has recently been described as a mesenchyme disorder that affects the connective tissue of an individual. Autosomal dominant and recessive forms of the disorder have been reported, although most cases are autosomal dominant. Reports have found that in Western societies, Larsen syndrome can be found in one in every 100,000 births, but this is most likely an underestimate because the disorder is frequently unrecognized or misdiagnosed.
1p36 deletion syndrome is a congenital genetic disorder characterized by moderate to severe intellectual disability, delayed growth, hypotonia, seizures, limited speech ability, malformations, hearing and vision impairment, and distinct facial features. The symptoms may vary, depending on the exact location of the chromosomal deletion.
Tetrasomy 18p is a genetic condition that is caused by the presence of an isochromosome composed of two copies of the short arm of chromosome 18 in addition to the two normal copies of the chromosome. It is characterized by multiple medical and developmental concerns.
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.
8p23.1 duplication syndrome is a rare genetic disorder caused by a duplication of a region from human chromosome 8. This duplication syndrome has an estimated prevalence of 1 in 64,000 births and is the reciprocal of the 8p23.1 deletion syndrome. The 8p23.1 duplication is associated with a variable phenotype including one or more of speech delay, developmental delay, mild dysmorphism, with prominent forehead and arched eyebrows, and congenital heart disease (CHD).
1q21.1 deletion syndrome is a rare aberration of chromosome 1. A human cell has one pair of identical chromosomes on chromosome 1. With the 1q21.1 deletion syndrome, one chromosome of the pair is not complete, because a part of the sequence of the chromosome is missing. One chromosome has the normal length and the other is too short.
1q21.1 duplication syndrome or 1q21.1 (recurrent) microduplication is a rare aberration of chromosome 1.
Distal 18q- is a genetic condition caused by a deletion of genetic material within one of the two copies of chromosome 18. The deletion involves the distal section of 18q and typically extends to the tip of the long arm of chromosome 18.
Ring chromosome 18 is a genetic condition caused by a deletion of the two ends of chromosome 18 followed by the formation of a ring-shaped chromosome. It was first reported in 1964.
1q21.1 copy number variations (CNVs) are rare aberrations of human chromosome 1.
22q11.2 distal deletion syndrome is a rare genetic condition caused by a tiny missing part of one of the body’s 46 chromosomes – chromosome 22. 22q11.2 distal deletion syndrome appears to be a recurrent genomic disorder distinct from DiGeorge syndrome and velocardiofacial syndrome.
Chromosomal deletion syndromes result from deletion of parts of chromosomes. Depending on the location, size, and whom the deletion is inherited from, there are a few known different variations of chromosome deletions. Chromosomal deletion syndromes typically involve larger deletions that are visible using karyotyping techniques. Smaller deletions result in Microdeletion syndrome, which are detected using fluorescence in situ hybridization (FISH)
13q deletion syndrome is a rare genetic disease caused by the deletion of some or all of the large arm of human chromosome 13. Depending upon the size and location of the deletion on chromosome 13, the physical and mental manifestations will vary. It has the potential to cause intellectual disability and congenital malformations that affect a variety of organ systems. Because of the rarity of the disease in addition to the variations in the disease, the specific genes that cause this disease are unknown. This disease is also known as:
Fryns-Aftimos syndrome is rare chromosomal condition and is associated with pachygyria, severe mental retardation, epilepsy and characteristic facial features. This syndrome is a malformation syndrome, characterized by numerous facial dysmorphias not limited to hypertelorism, iris or retinal coloboma, cleft lip, and congenital heart defects. This syndrome has been seen in 30 unrelated people. Characterized by a de novo mutation located on chromosome 7p22, there is typically no family history prior to onset. The severity of the disorder can be determined by the size of the deletion on 7p22, enveloping the ACTB gene and surrounding genes, which is consistent with a contiguous gene deletion syndrome. Confirming a diagnosis of Fryns-Aftimos syndrome typically consists of serial single-gene testing or multigene panel of genes of interest or exome sequencing.
Ring chromosome 15 is a condition that arises when chromosome 15 fuses to form a ring chromosome. Usually, r15 forms due to modifications or deletion of genes on chromosome 15 in the preliminary stages of embryonic development but it can rarely also be inherited.
17q12 microdeletion syndrome, also known as 17q12 deletion syndrome, is a rare chromosomal anomaly caused by the deletion of a small amount of material from a region in the long arm of chromosome 17. It is typified by deletion of the HNF1B gene, resulting in kidney abnormalities and renal cysts and diabetes syndrome. It also has neurocognitive effects, and has been implicated as a genetic factor for autism and schizophrenia.
References
- ↑ Cody JD, Sebold C, Malik A, Heard P, Carter E, Crandall A, Soileau B, Semrud-Clikeman M, Cody CM, Hardies LJ, Li J, Lancaster J, Fox PT, Stratton RF, Perry B, Hale DE (2007). Am J Med Genet 143A(11):1181-90.