Find the incorrect statement among the following:

• A
  In sex-linked recessive traits,the gene is transmitted from an unaffected carrier female to some of the male progeny.
• B
  Accumulation of phenylpyruvic acid in the brain results in mental retardation.
• C
  Individuals affected by Down's Syndrome will have congenital heart defects and are more intelligent.
• D
  Turner's Syndrome is caused due to the absence of one $X$-chromosome.