出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2016/03/04 02:37:21」(JST)
Familial dysautonomia | |
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Facial features of a patient with familial dysautonomia over time. Note flattening of upper lip. By age 10 years prominence of lower jaw is apparent and by age 19 years there is mild erosion of right nostril due to inadvertent self-mutilation.
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Classification and external resources | |
Specialty | neurology |
ICD-10 | G90.1 |
ICD-9-CM | 742.8 |
OMIM | 223900 |
DiseasesDB | 11631 |
MedlinePlus | 001387 |
eMedicine | oph/678 |
MeSH | D004402 |
GeneReviews |
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[edit on Wikidata]
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Familial dysautonomia (FD), sometimes called Riley–Day syndrome[1] and hereditary sensory and autonomic neuropathy type III (HSAN-III) — is a disorder of the autonomic nervous system which affects the development and survival of sensory, sympathetic and some parasympathetic neurons in the autonomic and sensory nervous system resulting in variable symptoms including: insensitivity to pain, inability to produce tears, poor growth, and labile blood pressure (episodic hypertension and postural hypotension). People with FD have frequent vomiting crises, pneumonia, problems with speech and movement, difficulty swallowing, inappropriate perception of heat, pain, and taste, as well as unstable blood pressure and gastrointestinal dysmotility. FD does not affect intelligence. Originally reported by Conrad Milton Riley and Richard Lawrence Day in 1949,[2] FD is one example of a group of disorders known as hereditary sensory and autonomic neuropathies (HSAN).[3] All HSAN are characterized by widespread sensory dysfunction and variable autonomic dysfunction caused by incomplete development of sensory and autonomic neurons. The disorders are believed to be genetically distinct from each other.
Familial dysautonomia is seen almost exclusively in Ashkenazi Jews and is inherited in an autosomal recessive fashion. Both parents must be carriers in order for a child to be affected. The carrier frequency in Jewish individuals of Eastern European (Ashkenazi) ancestry is about 1/30, while the carrier frequency in non-Jewish individuals is unknown. If both parents are carriers, there is a one in four, or 25%, chance with each pregnancy for an affected child. Genetic counseling and genetic testing is recommended for families who may be carriers of familial dysautonomia.[citation needed]
Worldwide, there have been approximately 600 diagnoses recorded since discovery of the disease, with approximately 350 of them still living.[4]
Familial dysautonomia is the result of mutations in IKBKAP gene on chromosome 9, which encodes for the IKAP protein (IkB kinase complex associated protein). There have been three mutations in IKBKAP identified in individuals with FD. The most common FD-causing mutation occurs in intron 20 of the donor gene. Conversion of T→C in intron 20 of the donor gene resulted in shift splicing that generates an IKAP transcript lacking exon 20. Translation of this mRNA results in a truncated protein lacking all of the amino acids encoded in exons 20-37. Another less common mutation is a G→C conversion resulting in one amino acid mutation in 696, where Proline substitutes normal Arginine. The decreased amount of functional IKAP protein in cells causes familial dysautonomia.
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The most distinctive clinical feature is absence of overflow tears with emotional crying after age 7 months. This symptom can manifest less dramatically as persistent bilateral eye irritation. There is also a high prevalence of breech presentation. Other symptoms include weak or absent suck and poor tone, poor suck and misdirected swallowing, and red blotching of skin.
Symptoms in an older child with familial dysautonomia might include:
A clinical diagnosis of FD is supported by a constellation of criteria:
Genetic testing is performed on a small sample of blood from the tested individual. The DNA is examined with a designed probe specific to the known mutations. The accuracy of the test is above 99%. Dr. Anat Blumenfeld of the Hadasah Medical center in Jerusalem identified chromosome number 9 as the responsible chromosome.
Familial dysautonomia is inherited in an autosomal recessive pattern, which means 2 copies of the gene in each cell are altered. If both parents are shown to be carriers by genetic testing, there is a 25% chance that the child will produce FD. Prenatal diagnosis for pregnancies at increased risk for FD by amniocentesis (for 14–17 weeks) or chorionic villus sampling (for 10–11 weeks) is possible.
There currently is no cure for FD and death occurs in 50% of the affected individuals by age 30. There are only two treatment centers, one at New York University Hospital[5] and one at the Sheba Medical Center in Israel.[6] One is being planned for the San Francisco area.[7]
The survival rate and quality of life has increased since the mid 80s mostly due to greater understanding of the most dangerous symptoms. At present, FD patients can be expected to function independently if treatment is begun early and major disabilities avoided.
A major issue has been aspiration pneumonias, where food or regurgitated stomach content would be aspirated into the lungs causing infections. Fundoplications (by preventing regurgitation) and gastrostomy tubes (to provide non oral nutrition) have reduced the frequency of hospitalization.
Other issues which can be treated include FD crises, scoliosis, and various eye conditions due to limited or no tears.
An FD crisis is the body's loss of control of various autonomic nervous system functions including blood pressure, heart rate, and body temperature. Both short term and chronic periodic high or low blood pressure have consequences and medication is used to stabilize blood pressure.
Although the FD-causing gene has been identified and it seems to have tissue specific expression, there is no definitive treatment at present. Treatment of FD remains preventative, symptomatic and supportive. FD does not express itself in a consistent manner. The type and severity of symptoms displayed vary among patients and even at different ages on the same patients. So patients should have specialized individual treatment plans. Medications are used to control vomiting, eye dryness, and blood pressure. There are some commonly needed treatments including:
There is no cure for this genetic disorder.
It is noted that in cell lines derived from heterozygous carriers of FD who display a normal phenotype, there are decreased levels of the wild-type IKAP transcript and also functional IKAP protein respectively. This would suggest that increasing the amount of the wild-type IKAP transcript may improve the manifestation in patients with FD.
The outlook for patients with FD depends on the particular diagnostic category. Patients with chronic, progressive, generalized dysautonomia in the setting of central nervous system degeneration have a generally poor long-term prognosis. Death can occur from pneumonia, acute respiratory failure, or sudden cardiopulmonary arrest in such patients.
Parents and patients should generally be educated regarding daily eye care and early warning signs of corneal problems as well as use of punctual cautery. This education has resulted in decreased corneal scarring and need for more aggressive surgical measures such as tarsorrhaphy, conjunctival flaps, and corneal transplants.
In January 2001, researchers at Fordham University and Massachusetts General Hospital simultaneously reported finding the genetic mutation that causes FD, a discovery that opens the door to many diagnostic and treatment possibilities.[8][9]
Despite that it probably would not happen in the near future, some expect that stem-cell therapy will result. Eventually, treatment could be given in utero.[citation needed]
While that may be years ahead, genetic screening became available around April 2001, enabling Ashkenazi Jews to find out if they are carriers. Screening organization Dor Yeshorim offers testing as part of its panel, which also includes Tay-Sachs disease and cystic fibrosis.
In the meantime more research into treatments are being funded by the foundations that exist. These foundations are organized and run by parents of those with FD. There is no governmental support beyond recognizing those diagnosed with FD as eligible for certain programs.[10]
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リンク元 | 「ライリー・デイ症候群」「hereditary sensory and autonomic neuropathy type III」「familial dysautonomia」「Riley-Day症候群」 |
関連記事 | 「D」「day」「Da」「syndrome」 |
3型遺伝性感覚性自律神経性ニューロパチー、ライリー・デイ症候群
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