Multifactorial inheritance and recurrence risks of multiple sclerosis in Italian patients.

This study is based on 166 patients with definite multiple sclerosis (MS) residing in different Italian regions and on 332 parents and 326 siblings. Seven patients had a first-degree relative with a definite diagnosis. The comparison with a population age-matched for specific frequency of MS showed an increase of the disease among relatives. The increase in MS frequency among sibs is compared with that expected under an autosomal dominant, autosomal recessive or multifactorial model. The multifactorial hypothesis appears to better fit the data. The heritability index is calculated for each combination of relative and affected patient sex and compared with estimates of other European and American countries. The recurrence risk rates for male and female relatives have been computed for the more frequent family situations. Our results support the hypothesis of a multifactorial model of inheritance and provide risk figures to be used in genetic counseling.