As a result of prophylactic medical examination a 7-year-old boy was diagnosed with Lesch-Nyhan syndrome (only boys fall ill with it). The boy's parents are healthy but his grandfather by his mother's side suffers from the same disease. What type of disease inheritance is it?

Answer options

1. Semidominance
2. Recessive, sex-linked
3. Dominant, sex-linked
4. Autosomal recessive
5. Autosomal dominant

Explanation

Recessive inheritance means both genes in a pair must be abnormal to cause disease. People with only one defective gene in the pair are called carriers (the mother). These people are most often not affected by the condition. However, they can pass the abnormal gene to their children (son). It is sex-linked because it's from grandfather to son (only the male is involved).