Five patients from 4 unrelated Tunisian families who presented with disseminated neonatal infection by Mycobacterium bovis bacille Calmette-Guérin strain were investigated. Two unrelated patients had different homozygous interleukin-12 receptor beta1 subunit gene splice-site mutations (64+5G-->A and 550-2A-->G). Two siblings and 1 unrelated patient, all of whom were from the same town, carried the same mutation (297del8) within the interleukin-12p40 gene. This is the first description of familial cytokine deficiency reported so far. All patients had complete lack of expression of the affected polypeptide and a profound deficiency of in vitro interferon-gamma production. The clinical severity of the mycobacterial infection was heterogeneous, even among affected members of the same family, which suggests the intervention of modifying genes.
Paper AbstractObjective. The aim of the present study was to investigate whether the angiotensin-converting enzyme (ACE) insertion/deletion (I/D) polymorphism is associated with diabetic nephropathy and type 2 diabetes in the Tunisian population. Design. A case-control study was conducted among 141 unrelated type 2 diabetic patients with (90 patients) or without nephropathy (51 patients) and 103 non-diabetic controls with normal fasting blood glucose. Genotyping was performed using a nested polymerase chain reaction amplification in order to identify correctly heterozygous individuals.
NADPH oxidase, a multi-subunit protein consisting of cytosolic components and the membranebound heterodimer,plays an instrumental role in host defence mechanisms of phagocytes. Genetic deficiency of the enzymatic complex results in an inherited disorder, chronic granulomatous disease (CGD), which is characterized by an impaired phagocyte microbicidal activity. X-Linked (XL) CGD results from a mutation in the CYBB gene encoding the gp91phox subunit, while autosomal recessive (AR) CGD is associated with mutations in one of the NCF1, NCF2 and CYBA genes that encode the p47phox, p67phox and p22phox subunits, respectively. In the study reported here, we investigated genetic defects underlying CGD in 15 Tunisian patients from 14 unrelated families. Haplotype analyses and homozygosity mapping with microsatellite markers around known CGD genes assigned the genetic defect to NCF1 in four patients, to NCF2 in four patients and to CYBA in two patients. However, one family with two CGD patients seemed not to link the genetic defect to any known AR-CGD genes. Mutation screening identified two novel mutations in NCF2 and CYBA in addition to the recurrent mutation, DGT, in NCF1 and a splice site mutation previously reported in a North African patient. Our results revealed the genetic and mutational heterogeneity of the AR recessive form of CGD in Tunisia.
Mendelian susceptibility to mycobacterial disease (MSMD) is a rare disorder predisposing apparently healthy individuals to infections caused by weakly virulent mycobacteria such as bacille Calmette-Guerin (BCG), environmental mycobacteria, and poorly virulent Salmonella strains. IL-12p40 deficiency is the first reported human disease due to a cytokine gene defect and is one of the deficiencies that cause MSMD. Nine mutant alleles only have been identified in the IL12B gene, and three of them are recurrent mutations due to a founder effect in specific populations. IL-12p40 deficiency has been identified especially in countries where consanguinity is high and where BCG vaccination at birth is universal. We investigated, in such settings, the clinical, cellular, and molecular features of six IL-12p40-deficient Tunisian patients having the same mutation in IL12B gene (c.298_305del). We found that this mutation is inherited as a common founder mutation arousing ~1,100 years ago. This finding facilitates the development of a preventive approach by genetic counseling and prenatal diagnosis especially in affected families.
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