Question: A thirty-five-year-old man (index case) affected by ataxia and with clinical manifestations for three years, presents an expansive trinucleotide CAG mutation in heterozygosis in the ATXN1 gene. The molecular diagnosis is of spinocerebellar ataxia type 1 (SCA1; 6p22.3) and in the genetic report it is said that the disease is of complete penetrance throughout life. In genetic counseling, the risks of transmitting the disease to their offspring will be explained to the index case. What follows from the above? 
 Options:  <1> Being the male index case, all female descendants will inherit ataxia; but no male child. <2> The mutation will be transmitted to 50% of the descendants of the index case, who will develop ataxia from some point in their life. <3> The mutation will be transmitted to 25% of the descendants of the index case, who will develop ataxia from some point in their life. <4> The ataxia will be transmitted throughout the life of the index case affecting all of its offspring. <5> If the partner of the index case carries another SCA mutation (for example, in SCA36, great genetic heterogeneity), ataxia will be suffered by 25% of the descendants from some point in their life. If the couple is not a carrier, the ataxia will not be transmitted.
2