Neuropathy, Hereditary Sensory And Autonomic, Type Iii

A number sign (#) is used with this entry because hereditary sensory and autonomic neuropathy type III (HSAN3), or familial dysautonomia (FD), is caused by homozygous or compound heterozygous mutation in the IKBKAP gene (603722) on chromosome 9q31.

For a discussion of genetic heterogeneity of hereditary sensory and autonomic neuropathy, see HSAN1 (162400).

Clinical Features

Riley et al. (1949) first described this disorder in 5 Jewish patients with autonomic dysfunction and defective lacrimation. Other features included episodic hypertension, hyperhidrosis, cyclic vomiting, and skin blotching. Smith and Dancis (1963) noted the lack of an axon flare after intradermal histamine, and Smith et al. (1965) noted the absence of fungiform papillae on the tongue. These authors also described Ashkenazi Jewish heritage and decreased deep tendon reflexes.

In an extensive review of 210 children with familial dysautonomia from 172 families, Brunt and McKusick (1970) concluded that FD is an autosomal recessive disorder occurring almost exclusively in persons of Ashkenazi Jewish descent. Common features included alacrima, absence of lingual fungiform papillae with impaired taste, vasomotor instability, hypoactive or absent deep tendon reflexes, and relative indifference to pain and temperature. Patients showed incoordination, and neuropathic joints and scoliosis were often seen. Although emotional instability occurred, intellect was unimpaired. Patients also showed increased sensitivity to adrenergic and cholinergic agents, suggesting functional autonomic denervation. Axelrod et al. (1981) demonstrated clinical variability in sensory impairment among 75 patients with FD. Older patients tended to have increased dysfunction in pain sensation, joint position and Romberg sign, and vibratory sense. Testing after a 5-year interval showed significant worsening with increased age.

Pearson et al. (1980) demonstrated glomerulosclerosis in 10 or 13 autopsied and biopsied patients with familial dysautonomia. Sympathetic nerve terminals could not be identified in renal vessels from the patients, whereas they were demonstrated in controls. In a review of 79 patients, elevated serum creatinine (32% of patients) and blood urea nitrogen (76% of patients) were found, and an association was found between hypotension and renal dysfunction. Pearson et al. (1980) suggested that altered renovascular responsivity to systemic hypotension in the disorder may lead to ischemia and subsequent sclerosis of glomeruli.

In patients with FD, Gadoth et al. (1983) found a prolonged pupil cycle time (light response) and interpreted it as indicative of denervation hypersensitivity. Parenterally administered Mecholyl caused overflow tearing and temporary normalization of deep tendon reflexes and response to intradermal histamine, suggesting functional rather than structural denervation.

Axelrod and Abularrage (1982) reported on survival in dysautonomia. From 1969 to 1982, 227 patients had been referred to the Dysautonomia Center at New York University. At the time of report, 59 patients were 20 years of age or older and accounted for 33% of the living patients. The oldest was 38 years old. Axelrod (1998) provided an update of the patients at the Dysautonomia Center. In 1998, 40% of the active population of 307 patients were over the age of 20 years. In addition to worsening peripheral sensory dysfunction, the adults complained of poor balance, unsteady gait, and difficulty concentrating. They were prone to depression, anxieties, and even phobias. Sympathovagal balance became more precarious with worsening of orthostatic hypotension, development of supine hypertension, and even occasional bradyarrhythmias. Fishbein and Grossman (1986) described the pulmonary complications in a 29-year-old man with familial dysautonomia.

In an extensive review of HSAN3, Axelrod and Hilz (2003) noted that autonomic disturbances are very prominent, including alacrima, episodic hyperhidrosis, and vasomotor and cardiovascular perturbations. Patients can exhibit both extreme hypertension and profound and rapid postural hypotension without compensatory tachycardia. There is also a relative insensitivity to hypoxemia. Patients often experience episodes termed 'dysautonomic crises,' which are characterized by nausea and vomiting, agitation, tachycardia, and hypertension, and are often triggered by emotional or physical stress. Somatic growth is poor, and by 10 years of age, 85% of patients have scoliosis. Seizures with decerebrate posturing can follow breath-holding episodes.

Pathologic Findings

Brown et al. (1964) described autopsy findings in 2 Jewish sibs with HSAN3, which included demyelination in the medulla, pontine reticular formation, and dorsolongitudinal tracts, and degeneration, pigmentation, and loss of cells in autonomic ganglia.

Pearson et al. (1975) reported that sural nerve biopsy from patients with HSAN3 showed reduced transverse fascicular area, diminished numbers of myelinated axons, especially those of small diameter, and very few nonmyelinated axons. In addition, catecholamine-containing nerve endings were not identified in accompanying arteries. The authors noted that the changes were compatible with the clinical phenotype.

Pearson et al. (1978) stated that intrauterine development and postnatal maintenance of dorsal root ganglion neurons are abnormal in FD. They found that neurons in dorsal root ganglia were markedly diminished in young patients and continued to deplete with increasing age. Quantitative studies on C8 dorsal root ganglia showed that FD patients had as little as 10% the number of neurons as controls, with the smallest number being in the oldest patient. Lateral spinal root entry zones and loss of dorsal column myelinated axons were also found. The findings correlated with clinical features of diminished sensation and coordination of limb movements.

In adult patients with FD, Pearson and Pytel (1978) found that the mean volume of superior cervical sympathetic ganglia was reduced to 34% of normal. The mean totals of preganglionic neurons in the first 3 thoracic cord segments were reduced by about 50%. The authors noted that defects in sympathetic neurons account for many of the autonomic manifestations of the disorder.

Biochemical Features

Goodall et al. (1971) demonstrated a decrease in synthesis of noradrenaline in patients with FD. Weinshilboum and Axelrod (1971) found decreased dopamine-beta-hydroxylase (DBH; 223360), the enzyme that converts dopamine to norepinephrine. Some dysautonomic children had no plasma DBH activity and their mothers had decreased activity.

Pearson et al. (1982) reported anatomically discrete depletion of substance P (162320) immunoreactivity in the substantia gelatinosa of spinal cord and medulla of patients with familial dysautonomia. Substance P, an undecapeptide, is involved in transmission of nociceptive information at synapses of primary sensory neurons.

In patients with FD, Siggers et al. (1976) found a 3-fold increase in serum antigen levels of the nerve growth factor beta unit (NGFB; 162030) with normal function measurements, suggesting a qualitative abnormality of beta-NGF in the disorder. By bioimmunoassay of cultured fibroblasts from patients with FD, Schwartz and Breakefield (1980) found similar levels of beta-NGF compared to controls, but found that NGF showed about 10% activity compared to controls. The beta-adrenergic agonist isoproterenol produced no change in immunoreactive beta-NGF in dysautonomia, whereas it caused a marked increase in control cells. The authors postulated a defect in the processing of an NGFB precursor or in the structure of biologically active NGFB. In rats and guinea pigs, Johnson et al. (1980) showed that dorsal root ganglion neurons are destroyed by in utero exposure to maternal antibody to NGF. Using RFLP analysis of human NGFB and the NGF receptor (162010) to examine multiple FD families, Breakefield et al. (1984), Ozelius et al. (1986), and Breakefield et al. (1986) excluded both genes as the site of the FD disease mutation.

Pathogenesis

Lee et al. (2009) reported the derivation of patient-specific FD induced pluripotent stem cells (iPSCs) and the directed differentiation into cells of all 3 germ layers including peripheral neurons. Gene expression analysis in purified FD iPSC-derived lineages demonstrated tissue-specific missplicing of IKBKAP (603722) in vitro. Patient-specific neural crest precursors expressed particularly low levels of normal IKBKAP transcript, suggesting a mechanism for disease specificity. FD pathogenesis was further characterized by transcriptome analysis and cell-based assays revealing marked defects in neurogenic differentiation and migration behavior. Furthermore, Lee et al. (2009) used FD iPSCs for validating the potency of candidate drugs in reversing aberrant splicing and ameliorating neuronal differentiation and migration. Lee et al. (2009) concluded that their study illustrated the promise of iPSC technology for gaining new insights into human disease pathogenesis and treatment.

Diagnosis

Axelrod et al. (1983) stated that the clinical diagnosis of familial dysautonomia is based on the presence of 5 signs: lack of axon flare after intradermal injection of histamine, absence of fungiform papillae on the tongue, miosis of the pupil after conjunctival instillation of methacholine chloride (2.5%), absent deep tendon reflexes, and diminished tear flow. However, they noted that consistent neuropathologic findings in sural nerve biopsies may be the best diagnostic criterion to differentiate familial dysautonomia from other forms of congenital sensory neuropathy. Axelrod et al. (1983) reported the case of a gypsy child with congenital sensory neuropathy who had all 5 signs in addition to skeletal abnormalities, dysmorphic features, and hypohidrosis, but whose sural nerve biopsy was inconsistent with dysautonomia. The authors noted that many non-Jewish cases of 'familial dysautonomia' may be another form of congenital sensory neuropathy (e.g., 201300, 256800).

Axelrod et al. (1987) suggested that the possibility of familial dysautonomia should be suspected in a child of Eastern European Jewish extraction with breech delivery, meconium staining, poor suck, hypotonia, or hypothermia. The diagnosis could be confirmed by inspection of the tongue for fungiform papillae, determination of deep tendon reflexes, and performance of intradermal histamine and intraocular pilocarpine tests. If results in either of the latter 2 tests are normal or equivocal, they should be repeated after 6 weeks of age.

Prenatal Diagnosis

Eng et al. (1995) used CA-repeat polymorphisms located in the 9q31-q33 region for prenatal diagnosis of familial dysautonomia. All 7 families studied were informative for the markers, and fetal diagnoses were made in 8 pregnancies. Six fetal diagnoses were predicted with more than 98% accuracy, whereas 2 with recombinations were predicted with at least 88% and 92% accuracy.

Using linkage and linkage disequilibrium analyses with highly polymorphic dinucleotide repeat markers known to flank the familial dysautonomia locus, Oddoux et al. (1995) performed prenatal diagnosis in 8 pregnancies in 7 informative families. All of the fetuses were predicted to be heterozygous unaffected; 7 had come to term and were normal.

Clinical Management

The most prevalent causative mutation in FD is an IKBKAP splice site mutation that results in deletion of exon 20, producing a truncated protein (603722.0001). The polyphenol (-)-epigallocatechin gallate (EGCG) downregulates expression of HNRNPA2B1 (600124), a transactivating factor that encourages the use of intron-distal 5-prime splice sites. Anderson et al. (2003) found that EGCG treatment of cultured FD-derived fibroblasts increased the use of the intron-proximal splice site, resulting in the generation of more exon 20-containing IKBKAP transcript. EGCG did not alter IKBKAP splicing in normal cells. Anderson et al. (2003) observed synergistic production of correctly spliced transcript and full-length IKBKAP protein in FD fibroblasts treated with the combination of EGCG and tocotrienol, a vitamin E isoform that can upregulate transcription of the IKBKAP gene. They suggested that EGCG may be a therapeutic modality for individuals with FD.

Slaugenhaupt et al. (2004) showed that treating FD lymphoblast cells with the plant cytokinin kinetin altered splicing of IKBKAP. Kinetin significantly increased inclusion of exon 20 from the endogenous gene, as well as from an IKBKAP minigene, but did not enhance inclusion of alternatively spliced exon 31 in MYO5A (160777). Benzyladenine, the most closely related cytokinin, showed a similar but less dramatic effect.

Mapping

By family linkage studies, Blumenfeld et al. (1993) assigned the familial dysautonomia locus to chromosome 9q31-q33, with a maximum lod score of 21.1 at marker D9S58. Marker D9S58 also showed strong linkage disequilibrium with FD, with one allele present on 73% of affected chromosomes compared to 5.4% of controls. D9S53 and D9S105 represented the closest flanking markers.

Using 11 new polymorphic markers, Blumenfeld et al. (1999) narrowed the FD locus to less than 0.5 cM, between 2 specific markers. Two markers within this interval showed no recombination with the disorder. Haplotype analysis confirmed this candidate region and revealed a major haplotype shared by 435 of 441 FD chromosomes, indicating a striking founder effect. Three other haplotypes, found on the remaining 6 FD chromosomes, may have represented independent mutations. The frequency of the major FD haplotype in the Ashkenazim (5 in 324 control chromosomes) was consistent with the estimated FD carrier frequency of 1 in 32, and none of the 4 haplotypes associated with FD was observed on 492 non-FD chromosomes from obligatory carriers. The haplotype information made it possible to provide accurate genetic testing both for families with FD and for carriers on the basis of close flanking markers and the capacity to identify more than 98% of FD chromosomes by their haplotype.

Molecular Genetics

Slaugenhaupt et al. (2001) and Anderson et al. (2001) demonstrated that the major haplotype of familial dysautonomia is associated with a mutation in the IKBKAP gene (603722.0001). A minor haplotype was found to be associated with a different mutation (R696P; 603722.0002).

Population Genetics

In the United States, HSAN3 is a disorder almost completely limited to persons of Ashkenazi Jewish extraction (Brunt and McKusick, 1970). In Israel, as in the United States, most cases were Ashkenazim from Poland, according to Goldstein-Nieviazhski and Wallis (1966). Maayan et al. (1987) calculated an incidence of 1 in 3,703 for familial dysautonomia among Ashkenazi Jews in Israel.

Rare non-Jewish cases of presumed familial dysautonomia have been reported (e.g., Burke, 1966), but the diagnosis is usually in question. For example, the patient of Burke (1966) was later seen by Rogers (1993) who concluded that although the patient had a hereditary sensory neuropathy, the disorder was not familial dysautonomia. However, Leyne et al. (2003) identified a patient, previously described by Blumenfeld et al. (1999), who fulfilled all diagnostic criteria other than pure Ashkenazi Jewish ancestry (the patient's mother was of Irish-German/Sicilian heritage) and identified a novel mutation in the IKBKAP gene (603722.0003).

History

Axelrod (1998) provided a historical perspective on familial dysautonomia, highlighting the early contributions of Dancis. Recognition of this disorder, first described by Riley et al. (1949), spans almost 50 years.