FCN3 and attention deficit-hyperactivity disorder: In fact, the only individual that has been reported to be both FCN3 + 1637delC homozygous and of the O/O genotype was a premature baby (born at 35 weeks of gestation) with perinatal Streptococcus agalactiae infections, microcephaly, growth and mental retardation, and was diagnosed with attention deficit hyperactivity disorder (ADHD) at 3 years of age (Michalski et al. 2011).