The study, led by Robert Zivadinov, M.D., Ph.D., professor of neurology, has made the finding with the help of Magnetic resonance images (MRI).
The analyses were based on the MRIs of 759 consecutive MS patients, which showed that it is the patient's genetic make-up which plays a role not only in development but also in severity of the disease.
"From the early 1980s on, MS researchers thought that genetic factors likely played a role in the disease, that its traits were determined by several different genes, and our findings support this hypothesis," said Zivadinov.
"Our MRI analysis showed a difference between the severity of disease characteristics in familial MS patients versus what we call sporadic, or non-familial, MS patients," he said.
"These differences may be related to some disease-modifying genes, but to prove this, we must do further investigation," he added.
MS destroys myelin, the fatty sheath that protects nerve fibbers carrying message traffic from various muscles to and from the central nervous system.
This demyelization process leads to mild to serious disability, from slight numbness of the limbs to loss of vision and paralysis.
In the study, the 759 patients were in the age group of 36-56, with an average disability score of 3.4 on a scale of 0-10. A higher number indicating more disability.
Of the total patients, 478 had relapsing-remitting MS, involving acute attacks with full or partial recovery; while 222 had secondary-progressive MS, characterized by occasional attacks and sustained progression; 30 had primary-progressive MS with steady worsening from onset, and 29 had experienced their first attack.
198 were with a positive family history of MS.
The breakdown between first-, second- or third-degree relatives with MS was 81/35/82. All patients obtained full clinical and quantitative MRI evaluations.
Using MRI, researchers measured the number and volume of lesions (plaques), which represented areas of demeylination; atrophy of the whole brain, white matter (the neural pathways), grey matter (brain regions) and the cortex, as well as employing additional imaging techniques.
Between familial and sporadic cases based on age, disease duration, disease course, disability score and total lifetime use of disease-modifying drugs, they were not many differences.
"Patients whose parents, children or siblings [first-degree relatives] had MS showed more damage than patients who had cousins with MS, this indicates that the closer the relationship, the greater the risk of MS," Zivadinov said.