In our study there was a significantly higher incidence of a family history of premature CVD events in patients with MI age < 50 in comparison to patients with MI at age ≥ 50 and to healthy young people. Family history is a CAD risk factor independent from other risk factors. In the Malmo Diet and Cancer Study, family history of coronary heart disease (CHD) was associated with an incidence of CHD with a hazard ratio of 1.52 (95%CI: 1.39–1.65), and only a small proportion of the family history effect was mediated by hypertension, hyperlipidaemia and diabetes .
Although the highest cardiovascular risk was associated with a maternal history at age < 50 years and a paternal history at age < 55 years, no substantial differences were seen between maternal and paternal positive CVD history . In a Dutch Cohort study a particularly high incidence of CVD has been revealed in people with parental onset of MI before age 70, with maternal history of MI before age 60 being the strongest predictor of CVD incidence .
Offspring age of onset of CVD is significantly associated with both maternal and paternal age of CVD onset . Nevertheless, data regarding the role of a family history of CVD that includes relatives other than parents or the number of affected family members are scarce.
In our study, there were significant differences between MI < 50, MI ≥ 50 group and young healthy controls in positive family history of CVD involving not only the prevalence of premature CVD events restricted to parents but also such events in other the first- and the second-degree relatives. Moreover, there were statistically significant differences between the studied groups in the prevalence of CVD events at every age in family members (the first- and the second-degree relatives). A higher number of relatives with a positive history of CAD, including parents, children, siblings, siblings of parents and grandparents, was associated with a younger age of MI.
Interestingly, there was a clear negative correlation between the age of the first MI and the number of relatives with premature CVD events, and this relationship was particularly evident in the analysis involving the first-degree relatives, but not exclusively. An Italian study revealed that being a relative (including parents, siblings and siblings of parents) of an early-onset MI case confers an adjusted hazard ratio of 2.7 for such events . There are also data indicating that early-onset hypertension in grandparents raises the risk for hypertension in grandchildren, even after adjusting for early-onset hypertension in parents and for lifestyle factors .
Among other risk factors, the prevalence of smoking, BMI, HDL, LDL, TG and glucose levels differs significantly between the MI < 50 group and both control groups (MI ≥ 50 and healthy controls aged < 50) in our study. Such findings are independent of region and patient ethnicity across the literature [21, 22]. For instance, our data are in concordance with recently published data from New Zealand, conducted in a more complex population, including Caucasians, Maori and Pacific islanders . Although, among the risk factors for MI at a young age, smoking, hyperlipidaemia and obesity are crucial, there are some differences in their distribution between particular groups of patients [24, 25]. For example, the strongest predictor of ACS in women ≤ 45 years of age was diabetes, with a 6-fold increase in risk . Our study confirmed the significance of smoking, dyslipidaemia, obesity and carbohydrates metabolism disturbances as CAD risk factors.
The major limitation of our study is a relatively small number of patients, thus the findings are difficult to apply to a larger, more diverse population. On the other hand, the high homogeneity of the groups, limited to Polish population of a Caucasian race, could be of value regarding the potential population and racial differences in the pathogenesis of CAD, particularly taking into account heritable risk factors. The control group of young healthy blood donors, usually more educated and more conscious of lifestyle than general population, may not represent the community at large. On the other hand, the fact that donors stay free from CAD until the age of 50, whereas our young patients suffer from MI before this age, enhances the role of lifestyle in CAD prevention.