Insulin-like growth factor-1 (IGF-1) regulates several biological functions, and low plasma levels of IGF-1 are known to contribute towards the pathogenesis of rheumatoid arthritis (RA). In view of the biological significance of IGF-1, we investigated the association of RA with the polymorphism of a 192-bp allele which is cytosine-adenosine repeat located 1 kb upstream from the IGF-1 gene transcription site and is known to regulate serum IGF-1 levels.
Blood samples were collected from 52 healthy controls (HC) and 68 RA patients to measure the levels of IGF-1 and to isolate genomic DNA. Polymorphism of the IGF-1 gene was examined using polymerase chain reaction (PCR). Disease severity, duration, and activity were recorded for all RA patients.
We observed that 97% of all the subjects who participated in this study showed the presence of a 192-bp allele of the IGF-1 gene. All healthy controls exhibited the presence of 192-bp wild-type allele. All non-carriers of the 192-bp allele were Arabs and had RA. Gender correlated significantly with allele frequencies as 14% of the male and only 2% of the female RA patients were non-carriers of 192-bp allele. Plasma IGF-1 levels were significantly lower (p < 0.01) in RA patients compared to HC, and all RA patients who were non-carriers of the 192-bp allele had a significantly high disease activity score. No correlation was found between the duration of RA and the presence or absence of this allele.
This study suggests a possible association of the IGF-1 gene polymorphism with developing RA, particularly in males as non-carriers of the 192-bp allele.