A c.3216_3217delGA mutation in AGL gene in Tunisian patients with a glycogen storage disease type III: evidence of a founder effect.

Glycogen storage disease type III (GSD III) is an autosomal recessive disorder characterized by excessive accumulation of abnormal glycogen in the liver and muscles and caused by deficiency in the glycogen debranching enzyme, the amylo-1,6-glucosidase (AGL). In this study, we report the clinical, biochemical and genotyping features of five unrelated GSD III patients coming from the same region in Tunisia. The concentration of erythrocyte glycogen and AGL activity were measured by colorimetric and fluorimetric methods, respectively. Four CA/TG microsatellite markers flanking the AGL gene in chromosome 1 were amplified with fluoresceinated primers. The full coding exons and their relevant exon-intron boundaries of the AGL gene were directly sequenced for the patients and their parents. All patients showed a striking increase of erythrocytes glycogen content. No AGL activity was detected in peripheral leukocytes. Sequencing of the AGL gene identified a c.3216_3217delGA (p.Glu1072AspfsX36) mutation in the five patients which leads to a premature termination, abolishing the AGL activity. Haplotype analysis showed that the mutation was associated with a common homozygote haplotype. Our results suggested the existence of a founder effect responsible for GSD III in this region of Tunisia.

[Clinical and genetic characteristics of Buschke-Fischer-Brauer's disease in a Tunisian family]. / Etude clinique et génétique de la kératodermie palmoplantaire de Buschke-Fischer-Brauer dans une famille tunisienne.

BACKGROUND: Punctate palmoplantar keratoderma (PPPK), or Buschke-Fischer-Brauer's disease, is a rare form of genodermatosis with autosomal dominant transmission and with variable penetrance. Its molecular basis remains unknown. Two loci were found to be linked to this disease: one on 15q22 and the other on 8q24. We report the clinical and genetic characteristics of PPPK in a Tunisian family. PATIENTS AND METHODS: A Tunisian family with PPPK was identified through a proband. As far as possible, history taking, physical examination, histopathological tests and blood sampling for DNA extraction were carried out for each patient. RESULTS: Seventeen patients were included in this study. Age ranged from 15 to 81 years with a sex-ratio of 3.2 m/f. Lesions appeared between the ages of 10 and 65 years and at a mean of 28 years. Clinically, lesions ranged from few keratotic papules on the palms to coalescence of lesions in plaques over palmar and/or plantar surfaces. Hyperhydrosis, hypopigmented macules and nail dystrophy were frequently associated. In all patients, histopathological examination revealed thickening of the epidermis with compact orthohyperkeratosis overlying a small and sharply demarcated area of depressed epidermis. Mechanical measures and keratolytic ointments proved non-beneficial. Genotyping for chromosomes 8 and 15 as well as LOD scores confirmed genetic linkage with the suspected locus on chromosome 15q, with the interval of the locus in question reduced to 3.26 Mb. This region is flanked by markers D15S987 and D15S153. CONCLUSION: Our study of this family confirmed the classical characteristics of KPP-BFB as well as demonstrating several associated clinical signs of which the significance will be determined in subsequent studies. Further screening studies to identify mutated genes in the region of interest will help us to understand the molecular basis of this disease and hopefully to propose suitable treatment.

Placental mesenchymal dysplasia with beckwith-wiedemann syndrome fetus in the context of biparental and androgenic cell lines.

Placental mesenchymal dysplasia (PMD) is a distinct placental disorder that may coexist with a normal fetus. In one-third of cases, the fetus exhibits Beckwith-Wiedemann Syndrome (BWS). In the present study, we report a case of PMD changes associated with an unusual genetic constitution. Pathological examination showed an enlarged placenta with a mixture of normal but also numerous clusters of grape-like fluid-filled vesicles confined to the stem villi without trophoblast proliferation. Some stem villi contained many large vessels filled by partially organized thrombi consistent with PMD. The fetus presented an enlarged liver and cytomegaly in the adrenal glands, hyperplastic islets of Langerhans in the pancreas, and some microcysts with cuboidal epithelium in the kidneys. These findings suggest the Beckwith-Wiedemann syndrome phenotype. DNA genetic markers showed three alleles for three independent markers and two alleles for the 12 others. Fluorescent in situ hybridization (FISH) demonstrated that villous trophoblast and fetal tissues are diploid. The haploid paternal complement found in the androgenetic cells was different from that found in biparental cells, suggesting a double fertilization event. Preferential distribution of the androgenetic cells into the placenta explains the predominance of molar villi with an apparently normal fetus. This represents a well-documented case of androgenic and biparental mixture of cell types in both fetal and placental tissues.