Raffaello Guarinello                              Gianluca Signorini, Sampdoria Genua, 1999

 

Raffaello Guarinello                    Giorgio Rognoni                            Guido VincenziIn

In summary, the systematic analysis of new cases of ALS in the occupational group of Italian profession footballers identified an increased risk of ALS. The results of the neurological study permit the conclusion that professional football is a significant risk factor for ALS. The risk of ALS increases with the duration of professional playing for more than 5 years. The causes of the increased disease risk in Italian footballers are as yet unknown. Several hypotheses can be considered as possible causes:

• The disease risk of ALS refers to the physical activity and is independent of the type of sport and thus of football in the narrower sense.
• The ALS risk is specific to football and is attributable to microtrauma, e.g. associated with heading the ball, leg injuries or certain training concepts or procedures in physical treatment.
• The disease risk results from the use of illegal substances that are used to increase physical performance (“doping“).
• The increase in the frequency of ALS is associated with football specific environmental factors, e.g. the use of insecticides or fertilisers on football pitches and in stadiums.
• The increased ALS risk is due to genetic factors that are associated with above average physical performance. It can be assumed that the genetic factors for increased performance exert a negative influence on the function of motor nerve cells. It can be argued that these genetic factors are present in the general population but are over represented among professional footballers.

It should be noted that the demonstration of an increased ALS risk is based on an initial systematic analysis. This study was conducted in Italy only so that information about the actual disease risk of footballers in general and therefore in Germany also is still uncertain. To clarify this question, an investigation of the risk of ALS in Germany and other European countries in cooperation with the national football associations is necessary.

ALS and physical activity
The association between physical activity and an increased risk of developing ALS was already investigated in earlier studies. A twin study of 17 pairs of male twins showed a statistically increased rate of sporting activity in the affected sibling (Currier et al. Annals of Neurology, 1988;24:148). Another study of risk factors for ALS yielded a small but significant association between sporting activity and body weight and ALS. Compared with a control group of parallel sex and age, ALS patients had a higher rate of sporting activity and lower body weight. The data provide statistical evidence that ALS patients have greater physical activity and lower body weight before the onset of the disease. The association between body weight and ALS risk refers to investigation of the body mass index (BMI), which is derived from the weight and height of the person in question.
These statistical surveys support the neurological experience that ALS patients are predominantly physically active and slim persons. It should be stressed that a slim build and sporting activity should not be regarded as the cause of ALS. Physical exertion as a sole cause of the disease is without scientific basis. Studies to date show a small increase in ALS risk due to sporting activity, which is apparent as an increased probability of ALS with an odds ratio (OR) between 1.7 and 2.5.
The OR describes an increase in risk of the disease compared with the normal population. An OR of 2.0 describes a doubling of the risk of disease e.g. from 2 new cases/100,000 population to 4 new cases/100,000 population. According to what is known at present, physical activity can be assumed to be a possible risk factor in the complex make up of the causes of ALS. ALS must be regarded as a complex disease in which numerous genetic exogenous and stochastic factors coincide to cause the symptoms. It may be supposed that individual genetic and exogenous factors account for only a small percentage of e.g. 5–10% of the overall disease risk. This pathogenesis concept of ALS is supported by recent reports of an increased incidence of the disease in American soldiers actively deployed during the 1st Gulf War. A systematic analysis of 696,000 American soldiers undertaken since August 1990 showed that 40 persons have developed ALS.

In a similar group of American military relatives not deployed in the Gulf region, 67 new cases were found among 1.8 million persons (Horner et al. Neurology 2003; 61:742 49). The comprehensive epidemiological investigation shows a disease incidence of 3.6 per 100,000 inhabitants in Gulf War soldiers compared with a new disease rate of 1.4/100,000 among military relatives not deployed in the Gulf region. These data correspond with the scientific hypothesis that e.g. the increased physical activity or other hitherto unknown exogenous factors can make a small contribution to the multifactorial disease mechanisms of ALS.