Dynamic changes in IKBKAP mRNA levels during crisis of familial dysautonomia patients

Uncommon side effects of common drugs in patients with familial dysautonomia

PURPOSE

Patients with the autosomal recessive disorder of familial dysautonomia typically exhibit exacerbated adverse side effects to many common drugs. We aimed to catalog these adverse effects - with a focus on common drugs that are frequently administered to FD patients and compare their incidences to those within the general population.

METHODS

We used data of 595 FD patients from an international database with information on drugs received and adverse effects. To investigate the molecular causes of reported differences in drug responses in FD patients, we used expression microarrays to compare the mRNA expression profiles in peripheral blood leukocytes of FD patients (n = 12) and healthy individuals (n = 10).

RESULTS

Several drug classes, including cholinergics, anti-cholinergics, anti-convulsants, methylxanthines, SSRIs, and antibiotics caused either unreported symptoms or elevated rates of adverse events in FD patients. FD patients experienced different or more frequent adverse side effects than the general population in 31/123 drugs. These side effects included blood cell dyscrasias, amenorrhea, gastrointestinal bleeding, and bronchospasm. New findings include enhanced reaction of FD patients to H2 antagonist agents and to serotonin receptor agonists. We also detected eight genes differentially expressed between FD patients and healthy individuals that may underlie the differential drug responses of FD patients.

CONCLUSION

We provide evidence that suggests the use of several common drugs should be discontinued or reduced in FD patients.

Phosphatidylserine Ameliorates Neurodegenerative Symptoms and Enhances Axonal Transport in a Mouse Model of Familial Dysautonomia

Familial Dysautonomia (FD) is a neurodegenerative disease in which aberrant tissue-specific splicing of IKBKAP exon 20 leads to reduction of IKAP protein levels in neuronal tissues. Here we generated a conditional knockout (CKO) mouse in which exon 20 of IKBKAP is deleted in the nervous system. The CKO FD mice exhibit developmental delays, sensory abnormalities, and less organized dorsal root ganglia (DRGs) with attenuated axons compared to wild-type mice. Furthermore, the CKO FD DRGs show elevated HDAC6 levels, reduced acetylated α-tubulin, unstable microtubules, and impairment of axonal retrograde transport of nerve growth factor (NGF). These abnormalities in DRG properties underlie neuronal degeneration and FD symptoms. Phosphatidylserine treatment decreased HDAC6 levels and thus increased acetylation of α-tubulin. Further PS treatment resulted in recovery of axonal outgrowth and enhanced retrograde axonal transport by decreasing histone deacetylase 6 (HDAC6) levels and thus increasing acetylation of α-tubulin levels. Thus, we have identified the molecular pathway that leads to neurodegeneration in FD and have demonstrated that phosphatidylserine treatment has the potential to slow progression of neurodegeneration.

We create a novel FD mouse model, in which exon 20 of IKBKAP was deleted in the nervous system, to study the role of IKAP in the neurodegeneration process. The lack of IKBKAP exon 20 impaired retrograde nerve growth factor (NGF) transport and axonal outgrowth. Reduction of IKAP levels resulted in elevated HDAC6 levels and thus reduced acetylated α-tubulin levels. Phosphatidylserine down-regulated HDAC6 levels, furthermore phosphatidylserine treatment facilitated axonal transport and stabilized microtubules. In brief: Naftelberg et al. identify the molecular pathway leading to neurodegeneration using a mouse model of familial dysautonomia and suggest that phosphatidylserine acts as an HDAC6 inhibitor to improve neurologic function.

Familial Dysautonomia: Mechanisms and Models

Hereditary Sensory and Autonomic Neuropathies (HSANs) compose a heterogeneous group of genetic disorders characterized by sensory and autonomic dysfunctions. Familial Dysautonomia (FD), also known as HSAN III, is an autosomal recessive disorder that affects 1/3,600 live births in the Ashkenazi Jewish population. The major features of the disease are already present at birth and are attributed to abnormal development and progressive degeneration of the sensory and autonomic nervous systems. Despite clinical interventions, the disease is inevitably fatal. FD is caused by a point mutation in intron 20 of the IKBKAP gene that results in severe reduction in expression of IKAP, its encoded protein. In vitro and in vivo studies have shown that IKAP is involved in multiple intracellular processes, and suggest that failed target innervation and/or impaired neurotrophic retrograde transport are the primary causes of neuronal cell death in FD. However, FD is far more complex, and appears to affect several other organs and systems in addition to the peripheral nervous system. With the recent generation of mouse models that recapitulate the molecular and pathological features of the disease, it is now possible to further investigate the mechanisms underlying different aspects of the disorder, and to test novel therapeutic strategies.

Familial dysautonomia: History, genotype, phenotype and translational research

Familial dysautonomia (FD) is a rare neurological disorder caused by a splice mutation in the IKBKAP gene. The mutation arose in the 1500s within the small Jewish founder population in Eastern Europe and became prevalent during the period of rapid population expansion within the Pale of Settlement. The carrier rate is 1:32 in Jews descending from this region. The mutation results in a tissue-specific deficiency in IKAP, a protein involved in the development and survival of neurons. Patients homozygous for the mutations are born with multiple lesions affecting mostly sensory (afferent) fibers, which leads to widespread organ dysfunction and increased mortality. Neurodegenerative features of the disease include progressive optic atrophy and worsening gait ataxia. Here we review the progress made in the last decade to better understand the genotype and phenotype. We also discuss the challenges of conducting controlled clinical trials in this rare medically fragile population. Meanwhile, the search for better treatments as well as a neuroprotective agent is ongoing.

Tocotrienol Treatment in Familial Dysautonomia: Open-Label Pilot Study

Familial dysautonomia (FD) is an autosomal recessive congenital neuropathy, primarily presented in Ashkenazi Jews. The most common mutation in FD patients results from a single base pair substitution of an intronic splice site in the IKBKAP gene which disrupts normal mRNA splicing and leads to tissue-specific reduction of IKBKAP protein (IKAP). To date, treatment of FD patients remains preventative, symptomatic and supportive. Based on previous in vitro evidence that tocotrienols, members of the vitamin E family, upregulate transcription of the IKBKAP gene, we aimed to investigate whether a similar effects was observed in vivo. In the current study, we assessed the effects of tocotrienol treatment on FD patients' symptoms and IKBKAP expression in white blood cells. The initial daily doses of 50 or 100 mg tocotrienol, doubled after 3 months, was administered to 32 FD patients. Twenty-eight FD patients completed the 6-month study. The first 3 months of tocotrienol treatment was associated with a significant increase in IKBKAP expression level in FD patients' blood. Despite doubling the dose after the initial 3 months of treatment, IKBKAP expression level returned to baseline by the end of the 6-month treatment. Clinical improvement was noted in the reported clinical questionnaire (with regard to dizziness, bloching, sweating, number of pneumonia, cough episodes, and walking stability), however, no significant effect was observed in any clinical measurements (weight, height, oxygen saturation, blood pressure, tear production, histamine test, vibration threshold test, nerve conduction, and heart rate variability) following Tocotrienol treatment. In conclusion, tocotrienol treatment appears significantly beneficial by clinical evaluation for some FD patients in a few clinical parameters; however it was not significant by clinical measurements. This open-label study shows the complexity of effect of tocotrienol treatment on FD patients' clinical outcomes and on IKBKAP expression level compared to in vitro results. A longitudinal study with an increased sample size is required in the future to better understand tocotrienol affect on FD patients.