Mutant WD-repeat protein in triple-A syndrome.

Triple-A syndrome (MIM 231550; also known as Allgrove syndrome) is an autosomal recessive disorder characterized by adrenocorticotropin hormone (ACTH)-resistant adrenal insufficiency, achalasia of the oesophageal cardia and alacrima. Whereas several lines of evidence indicate that triple-A syndrome results from the abnormal development of the autonomic nervous system, late-onset progressive neurological symptoms (including cerebellar ataxia, peripheral neuropathy and mild dementia) suggest that the central nervous system may be involved in the disease as well. Using fine-mapping based on linkage disequilibrium in North African inbred families, we identified a short ancestral haplotype on chromosome 12q13 (<1 cM), sequenced a BAC contig encompassing the triple-A minimal region and identified a novel gene (AAAS) encoding a protein of 547 amino acids that is mutant in affected individuals. We found five homozygous truncating mutations in unrelated patients and ascribed the founder effect in North African families to a single splice-donor site mutation that occurred more than 2,400 years ago. The predicted product of AAAS, ALADIN (for alacrima-achalasia-adrenal insufficiency neurologic disorder), belongs to the WD-repeat family of regulatory proteins, indicating a new disease mechanism involved in triple-A syndrome. The expression of the gene in both neuroendocrine and cerebral structures points to a role in the normal development of the peripheral and central nervous systems.

Idiopathic achalasia is not allelic to alacrima achalasia adrenal insufficiency syndrome at the ALADIN locus.

BACKGROUND: Evidence indicates that patients with familial achalasia associated with Allgrove or triple-A syndrome (i.e. alacrima, achalasia and adrenocorticotropin-resistant adrenal insufficiency with neurological impairment) have mutations of the alacrima achalasia adrenal insufficiency syndrome (AAAS) gene. AIM: The present study was aimed at identifying possible AAAS gene mutations in patients with established idiopathic non-familial achalasia. METHODS: Genomic DNA of 41 patients was isolated from peripheral blood cells using standard methods. The 16 exons of the AAAS gene (or ALADIN) were screened for mutations using the denaturing high-performance liquid chromatography method. RESULTS: Four heterozygous nucleotidic variations have been identified in patients with idiopathic achalasia, among which three were exonic conservative polymorphisms [i.e. D138D (GAT-->GAC), L227L (TTG-->CTG) and F285F (TTC-->TTT) in exons 5, 7 and 9, respectively]. The fourth nucleotidic variation was located in intron 13 (IVS14-23delT). All variants have been regarded as polymorphisms resulting in a normal ALADIN protein since they are either conservative or lying outside the consensus splice sites. CONCLUSIONS: Our data do not support a pathogenetic role for common AAAS gene mutations in patients with idiopathic achalasia as seen in Allgrove syndrome. These findings suggest the participation of different mechanisms in the pathogenesis of idiopathic achalasia.

Spectrum of mutations of the AAAS gene in Allgrove syndrome: lack of mutations in six kindreds with isolated resistance to corticotropin.

Familial glucocorticoid deficiency due to corticotropin (ACTH) resistance consists of two distinct genetic syndromes that are both inherited as autosomal recessive traits: isolated ACTH resistance (iACTHR), which may be caused by inactivating mutations of the ACTH receptor (the MC2R gene) or mutations in an as yet unknown gene(s), and Allgrove syndrome (AS). The latter is also known as triple-A syndrome (MIM 231550). In three large cohorts of AS kindreds, the disease has been mapped to chromosome 12; most recently, mutations in the AAAS gene on 12q13 were found in these AS families. AAAS codes for the WD-repeat containing ALADIN (for alacrima-achalasia-adrenal insufficiency-neurologic disorder) protein. We investigated families with iACTHR (n = 4) and AS (n = 6) and a Bedouin family with ACTHR and a known defect of the TSH receptor. Four AS families were of mixed extraction from Puerto Rico (PR); most of the remaining six families were Caucasian families from North America (NA). Sequencing analysis found no MC2R genetic defects in any of the kindreds. No iACTHR kindreds, but all of AS families, had AAAS mutations. The previously reported IVS14+1G-->A splice donor mutation was found in all PR families, apparently due to a founder effect; one NA kindred was heterozygous for this mutation. In the latter family, long-range PCR failed to identify a deletion or other rearrangements of the AAAS gene. No other heterozygote or transmitting parent had any phenotype that could be considered part of AS. The IVS14+1G-->A mutation results in a premature termination of the predicted protein; although it was present in all PR families (in the homozygote state in three of them), there was substantial clinical variation between them. One PR family also carried a novel splice donor mutation of the AAAS gene in exon 11, IVS11+1G-->A; the proband was a compound heterozygote. A novel point mutation, 43C-->A(Gln15Lys), in exon 1 of the AAAS gene was identified in the homozygote state in a Canadian AS kindred with a milder AS phenotype. The predicted amino acid substitution in this family is located in a sequence that may participate in the preservation of stability of ALADIN beta-strands, whereas the splicing mutation in exon 11 may interfere with the formation of WD repeats in this molecule. We conclude that 1) AAAS does not appear to be frequently mutated in families with iACTHR; 2) AAAS is mutated in AS families from PR (that had previously been mapped to 12q13) and NA; and, 3) there is significant clinical variability between patients with the same AAAS defect.

Progressive bulbospinal amyotrophy in triple A syndrome with AAAS gene mutation.

Triple A (3A) syndrome, a rare autosomal recessive disorder, is characterized by adrenocorticotropic hormone-resistant adrenal insufficiency, achalasia of the cardia, alacrima, and variable autonomic and neurologic dysfunction. The gene responsible, AAAS, recently has been identified. We describe the neurologic phenotype of the first adult case of 3A syndrome presenting bulbospinal amyotrophy as the prominent sign in association with a homozygous nonsense mutation identified in the AAAS gene.

Phenotypic heterogeneity in AAAS gene mutation.

UNLABELLED: We report the cases of two sibs of North African origin with AAAS gene mutation characterized by the heterogeneity of their phenotype. While an 8-y-old boy presented with acute adrenal insufficiency and mental retardation, the diagnosis was suggested by the clinical history of his 6-y-old sister who had symptomatic achalasia and chronic adrenal failure. CONCLUSION: Our observations corroborate the phenotypic heterogeneity reported in triple A syndrome, and underline the possibility of a variable intra-familial expression.