Most diseases (or in this case I guess you would call it a 'condition') are not caused either by 100% genetic or environmental factors. It's a mix. For example, here's the current thinking on Type 1 (Insulin-dependent) Diabetes:
Quote:
The causes of type 1 diabetes are complex and still not completely understood. People with type 1 diabetes are thought to have an inherited, or genetic, predisposition to the disease. It is theorized that this genetic predisposition may remain dormant until it is activated by an environmental trigger such as a virus or a chemical. This starts an attack on the immune system that results in the eventual destruction of the beta cells of the pancreas.
So a Type 1 diabetic can't produce enough insulin, and they have to take insulin shots to make up for the lack.
Also, even if a condition is 'genetic' (100%) such as phenylketonuria, a metabolic disorder, does not mean it cannot be treated or prevented. In the case of PKU, avoiding phenylalanine in the diet prevents mental retardation in people with the disease.
So you are not necessarily 'stuck' with thin hair. It is up to you to decide to treat it, either with pharmaceuticals or alternative methods. It just depends on wether you think it is worth the money and inevitable risks.