CEBR1-10

Genetic variations of ADAM33 in normal versus asthmatic Saudi patients

Researchers:

Dr. Mohammad D. Bazzi (PhD)

ABSTRACT:

Asthma is the most prevalent pulmonary disease in the world affecting children and young adults; more than 300 million individuals suffer from this disease, and the prevalence of asthma is on the rise worldwide. Asthma is characterized by intermittent narrowing of the airways of the lung with subsequent reversible airflow obstruction; this airway narrowing causes symptoms such as coughing, wheezing, shortness of breath, and dyspnea. Clinically, asthma is heterogeneous disease for it is often associated with atopy, airway inflammation, and bronchial hyperresponsiveness (BHR). The pathology of asthma is characterized by a combination of hyperplasia and hypertrophy of the smooth muscle in both the small and large airways.

It is well-accepted now that asthma is a complex genetic disorder attributed to the interactions among many genes and between these genes and the environment. In the previous decade, several loci and more than 100 genes had been found to be associated with asthma in at least 1 population. Asthma and asthma-related traits (ASRT) have been mapped to mutations on chromosome 14 (ASRT1), chromosome 7 (ASRT2), chromosome 2 (ASRT3), chromosome 1 (ASRT4), chromosome 12 (ASRT5), and chromosome 17 (ASRT6). Furthermore, gene association studies have implicated a specific single nucleotide polymorphism (SNP) within several genes encoding proteins involved in immunological pathways of asthma such as T-lymphocyte-associated antigens, Th2 cytokines and their receptors, and other genes closely associated with airway function such as TNF-a, TNF-b, interleukins (4,9, and 13), suppressors of cytokine signaling, and glutathione-S-transferase.

Recently, a novel gene (ADAM33) has recently been identified as an important asthma candidate gene in Caucasians from several populations. Case-control and family-based association studies have also confirmed a potential link between polymorphisms of ADAM33 with asthma and BHR. ADAM33 gene, located on chromosome 20p13, codes for a member of the “a disintegrin and metalloprotease” family of proteins. The ADAM family of proteins is a subgroup of the metalloproteinase super-family implicated in cell–cell interactions, cell migration, cell adhesion, signal transduction, and the proteolytic removal of numerous transmembrane proteins. Several alternatively-spliced forms of ADAM33 are expressed in lung fibroblasts and bronchial smooth muscle. These findings suggest an important role for ADAM33, not only for asthma, but also as a general morphogenetic repair gene important for airway wall modeling and remodeling.

Since the manifestation of genetic disorders is complex processes involving genes and environment, each ethnically distinct population must be examined to know whether gene-disease association exists in that population. The objectives of this proposal are to document the genetic variations of ADAM33 in normal Saudi subjects as well asthmatic patients, and to assess whether these genetic variations are related to the susceptibility to asthma or BHR in Saudis.

OBJECTIVES:

There are several levels of objectives for our group depending on availability of resources (financial and technical). A long-term objective is to establish a world-class research center for examining the genetic basis of asthma among the people of Saudi Arabia. Accomplishing this objective should enable the identification of persons with predisposition and/or at high risk for the development of asthma, and should fasten the development of new diagnostic and therapeutic tools for the people of Saudi Arabia.

The immediate objectives of this research proposal are to determine the role that ADAM33 gene plays in the development of asthma in Saudi population. Initially, we plan on screening Saudi asthma patient for SNPs that have been reported to be associated with asthma in other populations [S1, S2, T1, T2, V-1, V4, F+1, ST+4 and ST+7; see literature-review section]. A recent study points to ADAM33 and ADAM8 as primary asthma genes (29), and hopefully, we shall examine the morphology of ADAM8 gene as well, time and resources permitting. Our specific research aims are:

1. Collect blood samples from patients as well as healthy subjects. We anticipate collecting samples from a minimum of 500 asthma patients plus an appropriate number of control subjects.
2. Classify the patient into standard subgroups [atopic-nonatopic, mild intermittent, mild persistent, or severe]. Such classification would be carried out by qualified physicians and according to the criteria of National Institutes of Health/Global Initiative for Asthma (5).
3. Determine important biochemical parameters such as serum IgE, eosinophil count, neutrophils, mast cells and macrophages.
4. Isolate DNA from the blood of all subjects (patients and control), and perform PCR to amplify regions corresponding to the above-mentioned SNPs
5. Determine the morphology of each SNP mentioned above
6. Perform statistical analysis to establish whether these SNPs (individually or in combinations) are associated with asthma or with any particular subgroup of patients

Extended objectives are sequence the entire gene of ADAM33 for certain cohorts and to examine the morphology of ADAM8 (and/or to sequence ADAM8 as well).For sequencing objectives, the gene will be divided into overlapping fragments to be amplified independently by PCR. The complete coding region of ADAM33, plus the intron/exon boundaries, will be sequenced to determine the frequency of various SNPs present, and to possibly identify new SNPs specific for the Saudi patients. We should be able to determine any possible associations between these variations (including the possible new ones) and asthma or any of its subgroup.