Distal 18q-

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Distal 18q-
9 year old girl with phenotypic features of de Grouchy syndrome (deletion 18p).jpg
A 9-year-old girl with phenotypic features of De Grouchy syndrome TYPE I (Monosomy 18p or deletion 18p or 18p-). This image does not show the phenotypic features of distal 18q (de Grouchy Type 2), which are quite distinct from those of Monosomy 18p
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Distal 18q- is a genetic condition caused by a deletion of genetic material within one of the two copies of chromosome 18. [1] The deletion involves the distal section of 18q and typically extends to the tip of the long arm of chromosome 18. [2]

Contents

Presentation

Distal 18q- causes a wide range of medical and developmental concerns, [3] with significant variation in severity due to the variation in breakpoints reported in individuals with distal 18q-. Current research is focused on establishing genotype-phenotype correlations to enable predictive genotyping.[ citation needed ]

Congenital anomalies

Heart abnormalities are present in 25–35% of people with distal 18q-. The majority of these defects are septal. Congenital orthopedic anomalies are also relatively common, particularly rocker-bottom feet or clubfoot. Cleft lip and palate are relatively common in people with distal 18q-. Kidney abnormalities have also been reported and include horseshoe kidney, hydronephrosis, polycystic kidney, and absent kidney. Boys with distal 18q- may have genital anomalies, the most frequent being cryptorchidism and hypospadias.[ citation needed ]

Neurologic

Hypotonia is a common finding. Around 10% of people with distal 18q- have seizures.

MRI abnormalities

Dysmyelination is a common finding in people with distal 18q-, present in about 95%. [4] Hypoplasia of the corpus callosum is also a common finding. [5]

Vision

Strabismus and nystagmus are prevalent in distal 18q-. Changes in the optic nerve, as well as colobomas, are also fairly common. Myopia has been reported in some individuals.[ citation needed ]

Ear and sinus infections

Due to changes in facial structures, infants, toddlers, and children with distal 18q- often have poor drainage from the middle ears, leading to a build-up of fluid. This can in turn lead to recurrent ear and sinus infections. Antibiotics are typically required to treat these infections. In addition, the diagnosis of ear infections in children with 18q- is frequently complicated by stenosis or atresia of the ear canals, a common finding in people with distal 18q-.[ citation needed ]

Hearing

People with distal 18q- frequently have conductive and/or sensorineural hearing loss. The degree of hearing loss may vary from mild to severe.

Gastrointestinal

Individuals with distal 18q- may have problems with reflux. Hernias have also been reported.

Genitourinary

As mentioned above, males with distal 18q- may have cryptorchidism. Hypospadias and chordee have also been reported. Also, a variety of kidney malformations have been reported in infants with distal 18q-, as noted above. Additionally, vesicouretereral reflux has been diagnosed in several people with distal 18q-.[ citation needed ]

Orthopedics

As mentioned above, distal 18q- is associated with an increased incidence of clubfoot and rocker bottom feet. Also, a significant chance of developing pes planus or pes cavus exists. People with distal 18q- frequently have overlapping toes. Scoliosis and genu varum are also known orthopedic complications in children and adults with distal 18q-.

Growth

Children and adults with distal 18q- are often small for their age. Many people with distal 18q- have an abnormal response to growth hormone stimulation. Those who have been treated with growth hormone have responded well to the treatment. [6] Microcephaly is also common in people with distal 18q-.

Thyroid

Hypothyroidism has been reported in some people with distal 18q-.

Immunology

Several people with distal 18q- have been diagnosed with low IgA levels, resulting in an increased incidence of infections.

Psychiatry

An increased incidence of psychiatric conditions occurs within the distal 18q- population. In one study, nearly 60% had depressive symptoms, 60% had symptoms of an anxiety disorder, 25% had manic symptoms, and 25% had psychotic symptoms. [7] However, this study included young patients, many of whom were too young to exhibit signs of certain psychiatric conditions. The typical age of onset for many of these conditions appears to be during the teen years. Thus, the results of this study may actually underestimate the true incidence of psychiatric conditions within this population. Outbursts, or anger issues, such as temper tantrums are also common.[ citation needed ]

Cognition and adaptive skills

97% of individuals possess some form of intellectual disability, ranging from moderate to severe cases. [8] [ failed verification ]

The intellectual development of individuals with distal 18q- vary quite widely. In one study of 46 individuals with distal 18q-, IQ ranged from 49 to 113, with most individuals falling in the mild to moderate range of intellectual disability. [9] Some of those with IQ scores on the lower end of the spectrum probably actually had deletions encompassing the TCF4 gene.

An increased incidence of autism is seen within the distal 18q- population. In a recent study, 45 of 105 individuals evaluated fell into the "possible" or "very likely" levels of risk for autism. [10] Adaptive skills may also be delayed in people with distal 18q-.

Dysmorphology

Common facial features include midfacial hypoplasia, short and downward- or upward-slanting palpebral fissures, epicanthic folds, and low-set ears with a prominent antihelix.

Genetics

Distal 18q- is a deletion of the long arm of chromosome 18. The majority of deletions have breakpoints between 45,405,887 and the tip of the chromosome. There are no common breakpoints, thus the size of the deletions vary widely. [2] The largest deletion reported is 30.076 Mb, while the smallest deletion reported to cause a clinical phenotype is 3.78 Mb. [2]

Diagnosis

Suspicion of a chromosome abnormality is typically raised due to the presence of developmental delays or birth defects. Diagnosis of distal 18q- is usually made from a blood sample. A routine chromosome analysis, or karyotype, is usually used to make the initial diagnosis, although it may also be made by microarray analysis. Increasingly, microarray analysis is also being used to clarify breakpoints. Prenatal diagnosis is possible using amniocentesis or chorionic villus sampling.[ citation needed ]

Treatment

At present, treatment for distal 18q- is symptomatic, meaning the focus is on treating the signs and symptoms of the conditions as they arise. To ensure early diagnosis and treatment, people with distal 18q- are suggested to undergo routine screenings for thyroid, hearing, and vision problems.[ citation needed ]

History

Distal 18q- was first described in 1964. [11] Originally, it was called "De Grouchy syndrome" or "De Grouchy syndrome 2". Today, the preferred nomenclature for this condition is 18q-. Since this condition was originally described, researchers have clarified the size and nature of these deletions. In general, deletions of 18q fall into one of two categories: interstitial deletions, which typically have breakpoints between 18q11.2 (18.9 Mb) to 18q21.1 (43.8 Mb), and terminal deletions, which typically have a breakpoint distal to 18q21.1 (45.4 Mb) and extend to the end of the chromosome. If possible, it is preferable to indicate the general location of the deletion with the phrases "proximal 18q-" and "distal 18q-".[ citation needed ]

Research

Currently, research is focusing on identifying the role of the genes on 18q in causing the signs and symptoms associated with distal deletions of 18q.

TCF4 – In 2007, deletions of or point mutations in this gene were identified as the cause of Pitt-Hopkins syndrome. [12] This is the first gene that has been definitively shown to directly cause a clinical phenotype when deleted. If a deletion includes the TCF4 gene (located at 55,222,331-55,664,787), features of Pitt-Hopkins may be present, including abnormal corpus callosum, short neck, small penis, accessory and wide-spaced nipples, broad or clubbed fingers, and sacral dimple. Those with deletions inclusive of TCF4 have a significantly more severe cognitive phenotype.[ citation needed ]

TSHZ1 - Point mutations and deletions of this gene are linked with congenital aural atresia. [13] Individuals with deletions inclusive of this gene have a 78% chance of having aural atresia.

Critical regions – Recent research has narrowed the critical regions for four features of the distal 18q- phenotype down to a small segment of distal 18q, although the precise genes responsible for those features remain to be identified.[ citation needed ]

The table below shows the established critical regions for four features of distal 18q-, as well as the penetrance for each of those features. [14] The penetrance figure represents the likelihood a person would have the feature given the critical region is deleted.[ citation needed ]

FeatureCritical RegionChromosome BandsPenetrance
Kidney malformation70,079,559-73,287,60418q22.3-q2325%
Dysmyelination71,669,548-73,287,60418q22.3-q23100%
Growth hormone response failure71,669,548-73,287,60418q22.3-q2390%

Haplolethal regions - Two regions on chromosome 18 have never been found to be deleted. They are located between the centromere and 22,826,284 bp (18q11.2) and between 43,832,732 and 45,297,446 bp (18q21.1). The genes in these regions are thought to be lethal when deleted.

See also

Related Research Articles

Langer–Giedion syndrome Medical condition

Langer–Giedion syndrome (LGS) is a very uncommon autosomal dominant genetic disorder caused by a deletion of a small section of material on chromosome 8. It is named after the two doctors who undertook the main research into the condition in the 1960s. Diagnosis is usually made at birth or in early childhood.

Jacobsen syndrome Medical condition

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.

Smith–Magenis Syndrome (SMS), also known as 17p- syndrome, is a microdeletion syndrome characterized by an abnormality in the short (p) arm of chromosome 17. It has features including intellectual disability, facial abnormalities, difficulty sleeping, and numerous behavioral problems such as self-harm. Smith–Magenis syndrome affects an estimated between 1 in 15,000 to 1 in 25,000 individuals.

VACTERL association Medical condition

The VACTERL association refers to a recognized group of birth defects which tend to co-occur. This pattern is a recognized association, as opposed to a syndrome, because there is no known pathogenetic cause to explain the grouped incidence.

DiGeorge syndrome Condition caused by a microdeletion on the long arm of chromosome 22

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.

22q13 deletion syndrome Rare genetic syndrome

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.

1p36 deletion syndrome Medical condition

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.

Angelman syndrome Genetic disorder caused by part of the mothers chromosome 15 being missing

Angelman syndrome or Angelman's syndrome (AS) is a genetic disorder that mainly affects the nervous system. Symptoms include a small head and a specific facial appearance, severe intellectual disability, developmental disability, limited to no functional speech, balance and movement problems, seizures, and sleep problems. Children usually have a happy personality and have a particular interest in water. The symptoms generally become noticeable by one year of age.

18p- Deletion of the short arm of chromosome 18

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.

Pitt–Hopkins syndrome Medical condition

Pitt–Hopkins syndrome (PTHS) is a rare genetic disorder characterized by developmental delay, epilepsy, distinctive facial features, and possible intermittent hyperventilation followed by apnea. As more is learned about Pitt–Hopkins, the developmental spectrum of the disorder is widening, and can also include difficulties with anxiety, autism, ADHD, and sensory disorders. It is associated with an abnormality within chromosome 18; specifically, it is caused by an insufficient expression of the TCF4 gene.

Fryns syndrome Medical condition

Fryns syndrome is an autosomal recessive multiple congenital anomaly syndrome that is usually lethal in the neonatal period. Fryns (1987) reviewed the syndrome.

8p23.1 duplication syndrome Medical condition

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 Medical condition

1q21.1 duplication syndrome or 1q21.1 (recurrent) microduplication is a rare aberration of chromosome 1.

22q11.2 duplication syndrome is a rare genetic disorder caused by a duplication of a segment at the end of chromosome 22.

Proximal 18q- is a rare genetic condition caused by a deletion of genetic material within one of the two copies of chromosome 18. This deletion involves the proximal section of the long arm of chromosome 18 somewhere between 18q11.2 to 18q21.1. Exact breakpoints vary.

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.

22q11.2 distal deletion syndrome Medical condition

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 syndrome Medical condition

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)

Ring chromosome 15 Medical condition

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.

References

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