All disease results from the interplay of genes and environment. DNA, whose mysteries are slowly being unravelled, is the blue-print of everything we are and everything we will be. Four base pairs- codons- genes- make proteins which control everything else. Infections: viruses, parasites, bacteria--in some cases Borrelia burdorferi, become environmental factors which interact within a genetically encoded milieu. The relative importance of heredity and environment vary greatly depending on the disease. For example, if you are born with the cystic fibrosis gene your fate is predetermined before you are born. On the other hand, as with many other diseases--cancers, diabetes, coronary heart disease, multiple sclerosis and others, this interplay of genes and environment is no so easy to predict.
Alzheimer's disease, multiple sclerosis, lupus, arthritis and many other diseases are not caused by Lyme disease, or at least directly, as many patients mistakenly believe. Lyme may be an environmental factor associated with many diseases.
Susceptibility to Lyme is genetically coded and so is the virulence of a particle strain of the Lyme bacteria. In general, patients with chronic Lyme disease have central nervous system (brain) involvement, more often than not. Their clinical features are all quite different.
Borrelia burdorferi, unlike most other bacteria, is able to readily cross the blood brain barrier-- taking up residence within the brain. Inside the brain the spirochetes are seen as: atypical cystic forms, granular forms, blebs, rolled forms, colonies, rings, stretched strands, spherules and others.
Associated neuro-inflamation is complex and has been well described. Inflammation occurs as Bb encounters local immune cells such as macrophages and dendritic cells. Cytokines and chemokines induce inflammatory responses. Other immune cells, killer T-cells and B cells are activated. Bb can invade local glial cells and astrocytes. OspA is upregulated which induces apoptosis (cell death). Neurotoxins are produced. Nitric oxide and quinolinic acid have neuro-toxic effects. Autoimmune reactions also occur. There are different models of autoimmunity. Perhaps both molecular mimicry and Innocent bystander mechanisms occur. Lyme spirochetes have been observed in patients with concomitant Alzheimer's disease. Lyme does not cause Alzheimer's disease.
Alzheimer's disease has been studied for many decades. Various genetic mechanisms have been clearly established. Pathologically, Alzheimer's is characterized by an accumulation of amyloid protein in the brain neurofibrillary "plaques and tangles" and tau proteins. In animal models it has been shown that Alzheimer's does not occur when the protein which regulates the degradation of amyloid precursor is up-regulated.
Alzheimer's disease is considered the most common type of dementia. Dementia is characterized by chronic, progressive, global loss of cognitive functions. Numerous forms of dementia have been described. BSE (mad cow disease) is called prion disease. It is associated with mutated proteins in the brain. Lewey body dementia is associated with Parkinson's disease.
Rare genetic disorders, such as forms of porphyria can be associated with dementia (The madness of King George). Dementia may be the result of min-strokes and many other syndromes to numerous to list here. These syndromes may appear similar in the peri-morbid state, but they have clear differences in the earlier stages of the disease.
Of course, dementia can be associated with infection. For example, HIV and chronic CNS fungal infection are established causes of dementia. The dementia which most closely resembles Lyme dementia--neuroborreliosis associated dementia, is the dementia of neuro-syphilis. Syphilitic dementia is called "general paresis" and is known to be the cause of death of many historical characters.
Thankfully, most patients with neuroborreliosis do not develop dementia. They may suffer with severe cognitive deficits but these deficits are not global in nature. Patients usually maintain the ability to perform most activities of daily living. Certain cognitive processes in most Lyme patients remain relatively unaffected. SPECT/PET scans show patchy dysfunction. In Alzheimer's disease, the scans are global--not spotty.
Make no mistake. Neuroborreliosis is a devastating disease. Its treatment remains challenging. Still, many patients experience remarkable recoveries/remissions.
Amongst many in the Lyme community there is a reductionist tendency to oversimplify and claim that everything is caused by Lyme disease. This is neither true nor helpful.
Both sides must learn to speak a common language to find areas of disagreement and agreement.