1471 delTTCT a Common Mutation of Tunisian Patients with Lysinuric Protein Intolerance.

BACKGROUND: Lysinuric protein intolerance is an inherited aminoaciduria caused by defective cationic amino acid transport. It is an autosomal recessive disease caused by mutations in the SLC7A 7 gene. The objective of this study was to identify the mutations of Tunisians patients in order to offer the genetic counseling and the prenatal diagnosis to families. METHODS: Five affected Tunisian children (4 girls and 1 boy) belonging to four consanguineous families were considered. The diagnosis was made based on the plasma for amino acids quantification by Ion Exchange chromatography, the DNA for mutational analysis by DHPLC and sequencing, and the amniotic fluid for prenatal diagnosis. RESULTS: For the 5 patients, clinical features were dominated by failure to thrive, bone marrow abnormalities, hepatosplenomegaly, and mental retardation. The diagnosis for all patients was confirmed by biochemical analysis with hyperammonemia, hyperexcretion of urinary dibasic amino acids, and a high amount of orotic acid in the urine. The 1471 delTTCT mutation was identified in exon 9 in the homozygous state for all Tunisian patients. Genetic counseling was performed for three out of four families, four heterozygous and two homozygous healthy siblings were identified. The result of prenatal diagnosis showed the presence of the 1471 de1TTCT mutation in the homozygous state for the third pregnancy and heterozygous state for the fourth. CONCLUSIONS: The 1471 deITTCT mutation seems to be a common mutation of Tunisian population. The identification of this specific mutation provides a tool for confirmatory diagnosis, genetic counseling, and prenatal diagnosis.

First report of a molecular prenatal diagnosis in a tunisian family with lysinuric protein intolerance.

Lysinuric protein intolerance (LPI, MIM# 222700) is an inherited aminoaciduria caused by defective transport of cationic amino acids (CAAs; arginine, lysine, ornithine) at the basolateral membrane of epithelial cells in the intestine and kidney. We report the first prenatal diagnosis by direct mutational analysis of LPI performed in a Tunisian family. An amniotic fluid sample was carried out at 16 weeks of gestation in a 32-year-old Tunisian woman who consulted for prenatal diagnosis. The 1471 delTTCT mutation at homozygous state was identified indicating that the fetus was affected by LPI. The identification of this specific mutation provides a tool, which can be easily applied in Tunisia for molecular diagnosis, genetic counseling, and prenatal diagnosis of LPI.

Genetic heterogeneity of megaloblastic anaemia type 1 in Tunisian patients.

Megaloblastic anaemia 1 (MGA1) is a rare autosomal recessive condition characterized by selective intestinal vitamin B12 malabsorption and proteinuria. More than 200 MGA1 patients have been identified worldwide, but the disease is relatively prevalent in Finland, Norway and several Eastern Mediterranean regions. MGA1 is genetically heterogeneous and can be caused by mutations in either the cubilin (CUBN) or the amnionless (AMN) gene. In the present study we investigated the molecular defect underlying MGA1 in nine Tunisian patients belonging to six unrelated consanguineous families. Haplotype and linkage analyses, using microsatellite markers surrounding both CUBN and AMN genes, indicated that four out of the six families were likely to be linked to the CUBN gene. Patients from these families were screened for the Finnish, Mediterranean and Arabian mutations already published. None of the screened mutations could be detected in our population. One family showed a linkage to AMN gene. Direct screening of the AMN gene allowed the identification of the c.208-2A>G mutation, previously described in a Jewish Israeli patient of Tunisian origin and in Turkish patients. This suggests that the c.208-2A>G mutation may derive from a single Mediterranean founder ancestor. For the last family, haplotype analysis excluded both CUBN and AMN genes, suggesting the existence of a third locus that may cause MGA1.

Further evidence of the clinical and genetic heterogeneity of recessive transgressive PPK in the Mediterranean region.

Transgressive palmoplantar keratoderma (PPK) is the phenotypic hallmark of Mal de Meleda (MDM, MIM 24300). It is characterized by erythema and hyperkeratosis that extend to the dorsal face of the hands and feet. The disease is distributed worldwide and includes the Mediterranean population. The gene responsible for MDM, ARS (component B) mapped on chromosome 8qter, encodes for the SLURP-1 protein (Ly-6/uPAR related protein-1). A variety of mutations within the ARS gene have been shown to underlie MDM in different populations. Genetic heterogeneity of MDM is suspected. We have recently shown that three different homozygous mutations (82delT, C77R, C99Y) were responsible for MDM in 17 patients from Northern Tunisia belonging to eight unrelated consanguineous families. We report here a Tunisian family with three siblings presenting with recessive transgressive PPK closely resembling the MDM phenotype that excludes linkage to the ARS gene.

[Molecular study of Fanconi anemia in Tunisia]. / Etude moleculaire de l'anémie de Fanconi en Tunisie.

Fanconi anemia (FA) is an autosomal recessive rare disease characterized by progressive pancytopenia, congenital malformations and predisposition to acute myeloid leukemia. Fanconi anemia is genetically heterogeneous, with at least eight complementation groups of FA (FAA to FAD2). In order to characterize the molecular defects underlying FA in Tunisia, fourty-one families were genotyped with microsatellite markers linked to known FA gene. Haplotype analysis and homozygosity mapping showed that 92% of these families belong to FAA group. We demonstrated the effectiveness of the molecular analysis for a better selection of bone marrow graft donor and for the evaluation of chimerism after bone marrow transplantation. This study also allows genetic counselling for FA family members.

Fanconi anemia: contribution of molecular analyses to the identification of bone marrow graft donors and the study of chimerism in grafted patients.

We report on the effectiveness of molecular studies regarding Fanconi anemia (FA) for a better selection of bone marrow graft donors and for post-transplant follow up. Ten unrelated FA patients and their families were analyzed by microsatellite markers. In 9 cases, the cytogenetic investigation of potential human leukocyte antigen (HLA)-identical related donors was normal, and the molecular analyses confirmed that they were also either normal or heterozygous carriers. For 1 patient, cytogenetic analysis of an HLA-identical sibling donor yielded ambiguous results with a relatively high number of chromosomal breakages using cross-linking agents. However, genotyping of this potential donor demonstrated his heterozygous state. Nine patients have received allogeneic bone marrow transplantation from HLA-matched related donors. Microsatellite analysis showed complete chimerism (CC) in all cases. The median follow up was 54 months (range 8-144 months). One patient out of 9 with CC rejected her graft without prior detection of a transitional mixed chimerism. Among these patients, 1 died 25 months after the transplantation of a chronic graft-versus-host-disease (GVHD). We conclude that, when the cytogenetic studies are not conclusive, molecular analyses are crucial to distinguish heterozygous carriers from asymptomatic FA Tunisian patients. Molecular analyses also allowed the evaluation of hematopoietic chimerism after allogeneic bone marrow transplantation and might be of value to identify patients with a high risk for graft rejection.

Fanconi anemia in Tunisia: high prevalence of group A and identification of new FANCA mutations.

Fanconi anemia (FA) is a rare autosomal recessive disease characterized by progressive pancytopenia, congenital malformations, and predisposition to acute myeloid leukemia. Fanconi anemia is genetically heterogeneous, with at least eight distinct complementation groups of FA (A, B, C, D1, D2, E, F, and G) having been defined by somatic cell fusion studies. Six genes (FANCA, FANCC, FANCD2, FANCE, FANCG, and FANCF) have been cloned. Mutations of the seventh Fanconi anemia gene, BRCA2, have been shown to lead to FAD1 and probably FAB groups. In order to characterize the molecular defects underlying FA in Tunisia, 39 families were genotyped with microsatellite markers linked to known FA gene. Haplotype analysis and homozygosity mapping assigned 43 patients belonging to 34 families to the FAA group, whereas one family was probably not linked to the FANCA gene or to any known FA genes. For patients belonging to the FAA group, screening for mutations revealed four novel mutations: two small homozygous deletions 1693delT and 1751-1754del, which occurred in exon 17 and exon 19, respectively, and two transitions, viz., 513G-->A in exon 5 and A-->G at position 166 (IVS24+166A-->G) of intron 24. Two new polymorphisms were also identified in intron 24 (IVS24-5G/A and IVS24-6C/G).