Prenatal diagnosis of familial dysautonomia by analysis of linked CA-repeat polymorphisms on chromosome 9q31-q33

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.

Congenital insensitivity to pain—review and report of a case with dental implications

Pain is a protective mechanism for the body. Absence of pain is a symptom in several disorders, both congenital and acquired. The congenital types are present at birth and affect the number and distribution of types of nerve fibers. At present, 5 types of hereditary sensory and autonomic neuropathies have been identified. The various disorders within this group are classified according to the different patterns of sensory and autonomic dysfunction and peripheral neuropathy and the presence of additional clinical features such as learning disability. However, the field is currently moving away from classification based on clinical presentation toward classification based on underlying genetic abnormality. In the absence of pain, patients are at risk of late presentation with illnesses or injuries, and have an increased incidence of traumatic injury. Self-mutilation is an almost invariable feature of these disorders. We report the case of a patient with congenital insensitivity to pain that presented with self-mutilation injuries to his hands and oral tissues caused by biting. The severe nature of these injuries necessitated serial extraction of his primary teeth soon after eruption, which led to a cessation of the problem. The mutilation has not returned following the eruption of the first of his permanent teeth, suggesting that he has learned not to bite himself, even though to do so causes him no discomfort.

Familial dysautonomia: detection of the IKBKAP IVS20(+6T --> C) and R696P mutations and frequencies among Ashkenazi Jews

Familial dysautonomia (FD) is an autosomal recessive congenital neuropathy that occurs almost exclusively in the Ashkenazi Jewish (AJ) population. Mutations in the IkappaB kinase complex-associated protein (IKBKAP) gene cause FD. Two IKBKAP mutations, IVS20(+6T --> C) and R696P, have been identified in FD patients of AJ descent. The splice site mutation IVS20(+6T --> C) is responsible for > 99.5% of known AJ patients with FD, and haplotype analyses were consistent with a common founder. In contrast, the R696P mutation has been identified in only a few AJ patients. To facilitate carrier detection, a single PCR and allele-specific oligonucleotide (ASO) hybridization assay was developed to facilitate the detection of both the IVS20(+6T --> C) and R696P mutations. Screening of 2,518 anonymous AJ individuals from the New York metropolitan area revealed a carrier frequency for IVS20(+6T --> C) of 1 in 32 (3.2%; 95% CI, 2.5-3.9%), similar to the previously estimated carrier frequency (3.3%) based on disease incidence. No carrier was identified for the R696P lesion, indicating that the mutation was rare in this population (< 1 in 2,500). This sensitive and specific assay should facilitate carrier screening for FD mutations in the AJ community, as well as postnatal diagnostic testing.

Experiences in molecular-based prenatal screening for Ashkenazi Jewish genetic diseases

Multiple-option prenatal carrier testing in the Ashkenazi Jewish community for three and now eight disorders has been readily accepted in this prenatal, health-oriented and knowledgeable population. Counseling of screenees concerning the nature (severity, treatability, etc.), inheritance, and frequencies of each disorder was essential for informed test choices and future reproductive decision making. The value of couple testing for a group of disorders when 1 in about 6 would be found to be a carrier of at least one disease was emphasized. These studies identified issues of education, confidentiality, posttest anxiety, and self-esteem that must be continuously addressed in the Ashkenazi population. However, an important value of these studies is that they provide a framework for the development of mass carrier screening programs in the general population or in specific segments of the population with similar demographic characteristics and in more diverse prenatal populations.

Sympathetic skin response differentiates hereditary sensory autonomic neuropathies III and IV

OBJECTIVE

To evaluate whether sympathetic skin response (SSR) differs in patients with hereditary sensory autonomic neuropathy (HSAN) types III and IV.

BACKGROUND

HSAN types III and IV are rare autosomal recessive disorders that cause many similar autonomic, sensory, and motor dysfunctions, but different sweating characteristics. HSAN III patients have preserved and at times, excessive sweating, whereas anhidrosis is characteristic of HSAN IV. SSR reflects the integrity of sympathetic sudomotor fibers and the activation of sweat glands through the change in skin resistance in response to an arousal stimulus. Therefore, SSR is a test method that might facilitate differential diagnosis of HSAN III and IV.

METHODS

In 17 HSAN III patients (eight women, nine men; mean age, 20.65+/-5.45 years) and seven HSAN IV patients (five girls, two boys; mean age, 10.0+/-5.45 years) SSR was recorded from the palms and soles after repeated electrical, acoustic, and inspiratory gasp stimulations. In addition, all subjects underwent a neurologic examination; studies of median, peroneal motor, and sural nerve conduction velocities; and determination of vibratory and thermal perception thresholds.

RESULTS

Although clinical differences were appreciated between the two types of HSANs, both HSANs had evidence of small-fiber involvement. Both HSANs had abnormal temperature and pain perception. In contrast, SSR was preserved in all HSAN III and absent in all HSAN IV patients.

CONCLUSION

SSR provides another parameter to improve differentiation of HSAN III from HSAN IV, and also gives us additional information regarding sympathetic sudomotor fiber function in these developmental diseases.

Precise genetic mapping and haplotype analysis of the familial dysautonomia gene on human chromosome 9q31

Familial dysautonomia (FD) is an autosomal recessive disorder characterized by developmental arrest in the sensory and autonomic nervous systems and by Ashkenazi Jewish ancestry. We previously had mapped the defective gene (DYS) to an 11-cM segment of chromosome 9q31-33, flanked by D9S53 and D9S105. By using 11 new polymorphic loci, we now have narrowed the location of DYS to <0.5 cM between the markers 43B1GAGT and 157A3. Two markers in this interval, 164D1 and D9S1677, show no recombination with the disease. 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, might represent independent mutations. The frequency of the major FD haplotype in the Ashkenazim (5 in 324 control chromosomes) was consistent with the estimated DYS carrier frequency of 1 in 32, and none of the four haplotypes associated with FD was observed on 492 non-FD chromosomes from obligatory carriers. It is now 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 >98% of FD chromosomes by their haplotype.