Familial dysautonomia

Familial dysautonomia (FD) 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.

Familial dysautonomia
Other namesRiley–Day syndrome[1] and Hereditary sensory and autonomic neuropathy type III (HSAN-III)
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.
SpecialtyNeurology 

Originally reported by Drs. Conrad Milton Riley (1913–2005) and Richard Lawrence Day (1905–1989) 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.

Signs and symptoms

The most distinctive clinical feature is the 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:

  1. Delayed speech and walking
  2. Unsteady gait
  3. Spinal curvature
  4. Corneal abrasion
  5. Less perception in pain or temperature with nervous system.
  6. Poor growth
  7. Erratic or unstable blood pressure.
  8. Red puffy hands
  9. Dysautonomia crisis: a constellation of symptoms in response to physical and emotional stress; usually accompanied by vomiting, increased heart rate, increase in blood pressure, sweating, drooling, blotching of the skin and a negative change in personality.

Cause

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 by 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.

Diagnosis

Clinical diagnosis
Autosomal recessive inheritance

A clinical diagnosis of FD is supported by a constellation of criteria:

  • No fungiform papillae on the tongue
  • Decreased deep tendon reflexes
  • Lack of an axon flare following intradermal histamine
  • No overflow tears with emotional crying

Genetic testing

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 Hadassah Medical center in Jerusalem identified chromosome number 9 as the responsible chromosome.

Prenatal testing

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 have FD. For pregnancies at increased risk for FD, preimplantation genetic diagnosis or prenatal diagnosis by amniocentesis (at 15–17 weeks) or chorionic villus sampling (at 10–14 weeks) is possible.

Treatment

There is currently 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[4] and one at the Sheba Medical Center in Israel.[5] One is being planned for the San Francisco area.[6]

The survival rate and quality of life have increased since the mid-1980s mostly due to a 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 pneumonia, where food or regurgitated stomach content would be aspirated into the lungs causing infections. Fundoplications (by preventing regurgitation) and gastrostomy tubes (to provide nonoral 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.

Treatment of manifestations
Kyphoscoliosis in a 10-year-old girl with HSANIII

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:

  1. Artificial tears: using eye drops containing artificial tear solutions (methylcellulose)
  2. Feeding: Maintenance of adequate nutrition, avoidance of aspiration; thickened formula and different shaped nipples are used for baby.
  3. Daily chest physiotherapy (nebulization, bronchodilators, and postural drainage): for Chronic lung disease from recurrent aspiration pneumonia
  4. Special drug management of autonomic manifestations such as vomiting: intravenous or rectal diazepam (0.2 mg/kg q3h) and rectal chloral hydrate (30 mg/kg q6h)
  5. Protecting the child from injury (coping with decreased taste, temperature and pain perception)
  6. Combating orthostatic hypotension: hydration, leg exercise, frequent small meals, a high-salt diet, and drugs such as fludrocortisone.
  7. Treatment of orthopedic problems (tibial torsion and spinal curvature)
  8. Compensating for labile blood pressures

There is no cure for Familial Dysautonomia.

Prognosis

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 the use of punctal cautery. This education has resulted in decreased corneal scarring and need for more aggressive surgical measures such as tarsorrhaphy, conjunctival flaps, and corneal transplants.

Epidemiology

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 and Central 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.

Worldwide, there have been approximately 600 diagnoses recorded since discovery of the disease, with approximately 350 of them still living.[7]

Research

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.

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 to test as part of its panel, which also includes Tay–Sachs disease and cystic fibrosis.

In the meantime, more research into treatments is 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]

See also

References
  1. pediatriconcall.com Archived 2007-04-30 at the Wayback Machine
  2. Riley CM, Day RL, Greely D, Langford WS (1949). "Central autonomic dysfunction with defective lacrimation". Pediatrics. 3 (4): 468–77. PMID 18118947.
  3. Axelrod FB (2002). "Hereditary sensory and autonomic neuropathies. Familial dysautonomia and other HSANs". Clin Auton Res. 12. Suppl 1 (7): I2–14. doi:10.1007/s102860200014. PMID 12102459.
  4. Dysautonomia Treatment and Evaluation Center Archived 2006-01-14 at the Wayback Machine
  5. Sheba Medical Center
  6. "San Francisco To Get a Genetics Center - Forward.com". Retrieved 2007-11-02.
  7. "Archived copy". Archived from the original on 2009-04-18. Retrieved 2009-04-02.CS1 maint: archived copy as title (link)
  8. Anderson SL, Coli R, Daly IW, Kichula EA, Rork MJ, Volpi SA, Ekstein J, Rubin BY (2001). "Familial dysautonomia is caused by mutations of the IKAP gene". Am J Hum Genet. 68 (3): 753–8. doi:10.1086/318808. PMC 1274486. PMID 11179021.
  9. Slaugenhaupt SA, Blumenfeld A, Gill SP, Leyne M, Mull J, Cuajungco MP, Liebert CB, Chadwick B, Idelson M, Reznik L, Robbins C, Makalowska I, Brownstein M, Krappmann D, Scheidereit C, Maayan C, Axelrod FB, Gusella JF (2001). "Tissue-specific expression of a splicing mutation in the IKBKAP gene causes familial dysautonomia". Am J Hum Genet. 68 (3): 598–605. doi:10.1086/318810. PMC 1274473. PMID 11179008.
  10. Benefits for people with FD Archived 2011-07-26 at the Wayback Machine – from Dysautonomia foundation

Further reading


Classification
External resources
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