High-resolution transcript map of the region spanning D12S1629 and D12S312 at chromosome 12q13: triple A syndrome-linked region

Genomic organization of the region spanning D14Mit262 and D14Mit86 on mouse chromosome 14 and exclusion of Adam28 and Adamdec1 as the cataract-causing gene, lr2

Mice with recessive cataract, CXSD, show the first clinical symptoms of cataract at five weeks, with complete penetrance. We previously localized the cataract-causing lens rupture 2 gene (lr2) to mouse chromosome 14. In the process of positional cloning of the lr2 gene, we determined the genomic organization of the critical region, defined by D14Mit262 and D14Mit86, and compared it to recently published map information. In addition, mutational analysis using reverse transcription polymerase chain reaction (RT-PCR) followed by direct sequencing as well as quantitative realtime PCR (RQ-PCR) was performed to investigate Adam28 and Adamdec1 as lr2 candidate genes in this study. There was no mutation cosegregating with the phenotype of CXSD mice, which excluded these genes as the lr2 gene. Identification of more transcripts from this region and their mutation analyses are required to isolate the lr2 gene.

[Allgrove syndrome. Report on a family]

Triple A or Allgrove syndrome is a rare autosomal recessive disease with alacrima, achalasia, and ACTH-resistant adrenal insufficiency. It is usually associated with neurological disorders. Recently, mutations in the AAAS, a candidate gene mapped to chromosome 12q13, were identified. We report a family with seven affected siblings. All of them have signs of alacrima, four were operated on for achalasia, five have neurological abnormalities including cranial nerve abnormalities, amyotrophic lateral sclerosis, pyramidal syndrome, distal motor neuropathy, and amyotrophy, and two have adrenal insufficiency. Triple A syndrome should be considered in any young patient with alacrima.

An autosomal recessive exfoliative ichthyosis with linkage to chromosome 12q13

A new variant of congenital exfoliative ichthyosis in two related Bedouin families is reported. The ichthyosis appeared shortly after birth as a fine peeling of nonerythematous skin on the palms and soles. The prominent well-demarcated areas of denuded skin in moist and traumatized regions resembled the 'mauserung' phenomenon of ichthyosis bullosa of Siemens (IBS). Unlike in IBS, epidermolysis is absent on histological examination. Electron microscopy revealed a prominent intercellular oedema and numerous aggregates of keratin filaments in basal keratinocytes. Abnormal keratin (K) 1 expression was seen in the affected epidermis; however, all other keratins, including K2e, had a distribution comparable to that seen in normal controls. A maximum two-point LOD score of 2.53 and multipoint LOD score of 3.76 were obtained for marker D12S390, suggesting linkage to the type II keratin cluster on chromosome 12q13. Sequencing of both the K1 gene, the promotor and the 3' calcium regulatory region did not reveal a mutation. K2e and K5 genes, as well as the genes harboured within the minimal region, such as retinoic acid receptor gamma, sterol O-acyltransferase 2, integrin beta7 and insulin-like growth factor binding protein-6, were also excluded. This combination of clinical, histological, ultrastructural and genetic features has not been previously reported in other congenital exfoliative ichthyoses. We therefore suggest that it represents a new form of exfoliative ichthyosis.

New insights into the molecular basis of the triple A syndrome

The triple A syndrome (MIM*231550) is a rare autosomal recessive disorder characterized by adrenocorticotropic hormone (ACTH) resistant adrenal failure, achalasia, alacrima and a variety of neurological and dermatological features. Adrenal insufficiency usually presents in the first decade of life, however in some patients it may occur later in life or may even lack completely. Recently, we and others identified a novel gene on chromosome 12q13, designated AAAS (Achalasia-Addisonianism-Alacrima-Syndrome gene) which is mutated in patients with triple A syndrome. We investigated n=84 families including 111 patients with clinically suggested triple A syndrome and identified homozygous or compound heterozygous AAAS mutations in 78 families. Genotype/phenotype analyses revealed a highly variable occurrence, age of onset and severity of all clinical symptoms between patients with the same AAAS mutation. The obvious lack of a genotype/phenotype relationship is suggestive of modifying genes/factors which need to be determined. The AAAS protein function is unknown. With four WD repeats it belongs to the family of WD repeat-containing proteins which may exhibit a high degree of functional diversity. The subcellular localization of the protein and the determination of its putative binding partners will shed light on the role of the AAAS protein for the development and function of the adrenal gland and other neuroendocrine structures.

A novel human amino acid transporter, hNAT3: cDNA cloning, chromosomal mapping, genomic structure, expression, and functional characterization

Amino acid transporters are proteins that transport amino acids across the membrane. We report here the isolation and characterization of a novel human cDNA clone encoding a protein of 547 amino acids. This protein shares approximately 50% amino acid sequence homology with the amino acid transporters mouse mNAT and its orthologs, rat SN1 and human g17, and mouse GlnT/ATA1 and ATA2. Expression of this cRNA in Xenopus oocytes revealed that the strongest transport activities were specific for l-alanine. In addition, hNAT3 is a Na(+)- and pH-dependent, low-affinity transporter and partially tolerates substitution of Na(+) by Li(+). Since this protein has sequence and functional similarities to the previously identified system N amino acid transporters, we named this protein hNAT3. The genomic DNA sequence encoding the transcript of hNAT3 spans over 14 kb with 16 exons and 15 introns. Using fluorescence in situ hybridization, we mapped the hNAT3 gene to human chromosome 12q12-q13. By RT-PCR of embryonic and adult human tissues, hNAT3 was detected to be predominantly expressed in the liver and to a much lesser extent in the muscle, kidney, and pancreas. The data obtained in this study are likely to offer critical clues for identification of amino acid transporter-associated diseases.