Acta Neurol Scand. 2004 Apr;109(4):239-43
Department of Neurology, Harvard Medical School and Beth Israel Deaconess Medical Center, Boston, MA, USA
The unexpectedly low rate of concordance in monozygotic (MZ) twins with multiple sclerosis (MS) suggests that they share a systemic condition called the multiple sclerosis trait.
This trait constitutes the premorbid stage of the disease and is quite distinct from asymptomatic MS.
It results from the action of an antigenic challenge to the immune system of a genetically susceptible person but is short of producing lesions of the central nervous system parenchyma; in fact, the disease may never develop in people with the trait.
An environmental triggering event is required to transform the trait into the disease.
The discordance of clinical involvement and magnetic resonance images in MZ twins reflects differences in the effect of environmental influences.