Israel Medical Association Journal

Autoimmune diseases are classic examples of multifactorial disorders in which a large number of genes interact with environmental factors to form the final phenotype. Identification of the genes involved in these diseases is a daunting challenge. Initially the search involved the candidate approach where polymorphisms in suspected genes were tested for association in large cohorts of patients and controls. Today, the most widely used method is genome-wide association studies (GWAS), a method based on screening large panels of patients and controls with hundreds of thousands of single nucleotide polymorphisms (SNPs), with microarray-based technology. Unique families in which autoimmune diseases are caused by single genes are another alternative. The identification of candidate genes is often followed by studies that provide biologic plausibility for the findings. The widely expanding list of genes involved in autoimmune conditions show that the same genes frequently underlie the pathogenesis of different autoimmune diseases. Despite all available resources, the main void of heritability in autoimmune conditions is yet to be discovered. Identification of these genes will help define new biological pathways and identify novel targets for the development of new therapeutic drugs.

Background: Since the identification of the MEFV gene 198 mutations have been identified, not all of which are pathologic. The screening methods used in Israel to test patients suspected of having FMF include a kit that tests for the five main mutations (M694V, V726A, M680Ic/g, M694I, E148Q), and the sequencing of MEFV exon 10 in combination with restriction analysis for detecting additional mutations.

Objectives: To determine the contribution of testing for five additional mutations – A744S, K695R, M680Ic/t, R761H and P369S – to the molecular diagnosis of patients clinically suspected of having FMF.

Methods: A total of 1637 patients were tested for FMF mutations by sequencing exon 10 and performing restriction analysis for mutations E148Q and P369S.

Results: Nearly half the patients (812, 49.6%) did not have any detectable mutations, 581 (35.5%) had one mutation, 241 (14.7%) had two mutations, of whom 122 were homozygous and 119 compound heterozygous, and 3 had three mutations. Testing for the additional five mutations enabled us to identify 46 patients who would have been missed by the molecular diagnosis kit and 22 patients who would have been found to have only one mutation. Altogether, 4.3% of the patients would not have been diagnosed correctly by using only the kit that tests for the five main mutations.

Conclusions: This study suggests that testing for the additional five mutations as well as the five main mutations in patients with a clinical presentation of FMF adds significantly to the molecular diagnosis of FMF in the Israeli population.
 

Background: Cystinuria is an autosomal recessive disease that is manifested by kidney stones   and is caused by mutations in two genes: SLC3A1 on chromosome 2p and SLC7A9 on chromosome 19q. Urinary cystine levels in obligate carriers are often, but not always, helpful in identifying the causative gene.

Objectives: To characterize the clinical features and analyze the genetic basis of cystinuria in an inbred Moslem Arab Israeli family.

Methods: Family members were evaluated for urinary cystine and amino acid levels. DNA was initially analyzed with polymorphic markers close to the two genes and SLC7A9 was fully sequenced.

Results: Full segregation was found with the marker close to SLC7A9. Sequencing of this gene revealed a missense mutation, P482L, in the homozygous state in all three affected sibs.

Conclusions: A combination of urinary cystine levels in obligate carriers, segregation analysis with polymorphic markers, and sequencing can save time and resources in the search for cystinuria mutations.
 

Background: Primary pulmonary hypertension is a rare disorder, characterized by progressive pulmonary hypertension and right heart failure. It may be familial or sporadic. Mutations in bone morphogenetic protein receptor II (BMPR2), a member of the transforming growth factor-beta receptor superfamily of receptors, underlie many cases of the disorder.

Objectives: To perform molecular analysis of a patient with familial PPH[1] and provide her and her family with suitable genetic counseling.

Methods: DNA was extracted from 10 ml whole blood, and the BMPR2 gene was screened for mutations. Individual exons were amplified by polymerase chain reaction and sequenced. Mutation confirmation and molecular characterization of additional family members was performed using restriction enzyme analysis followed by appropriate genetic counseling.

Results: We identified a novel T to C missense mutation expected to result in substitution of arginine for a conserved cysteine in the ligand-binding domain of BMPR2. Screening of family members demonstrated the presence of the mutation in the father and a younger asymptomatic sister of the index patient.

Conclusions: Molecular diagnosis in PPH allows for identification of at-risk family members and raises the option of earlier diagnosis and possibly instituting earlier treatment in affected individuals. However, molecular screening of asymptomatic family members raises difficult ethical questions that can only be resolved by conducting large multicenter prospective studies in BMPR2 carriers.