biblatex-apa: sentence case not working

Question

Biblatex-Apa should automatically print titles in the reference list in sentence case, but for some reason it doesn't work (note the lowercase A after the colon):

\documentclass{article}

\usepackage[american]{babel}
\usepackage[utf8]{inputenc}

\usepackage[autostyle]{csquotes}
\usepackage[style=apa, backend=biber, natbib=true, firstinits=true, uniquename=init]{biblatex} 
\DeclareLanguageMapping{american}{american-apa}

\begin{filecontents}{case.bib}

@ARTICLE{Saetre2010,
  author = {Saetre, Peter and Lundmark, Per and Wang, August and Hansen, Thomas
    and Rasmussen, Henrik B. and Djurovic, Srdjan and Melle, Ingrid and
    Andreassen, Ole A. and Werge, Thomas and Agartz, Ingrid and Hall,
    Hakan and Terenius, Lars and Jonsson, Erik G.},
  title = {The Tryptophan Hydroxylase 1 ({TPH1}) Gene, Schizophrenia Susceptibility,
    and Suicidal Behavior: A Multi-Centre Case-Control Study and Meta-Analysis},
  journal = {American Journal of Medical Genetics, Part B: Neuropsychiatric Genetics},
  year = {2010},
  volume = {153B},
  pages = {387--396},
}

\end{filecontents}
\addbibresource{case.bib}

\begin{document}

\nocite{*}

\printbibliography[]

\end{document}

Answer 1

As mentioned by Audrey you should put the second part in the entry subtitle. The separator between title and subtitle is a colon. So your example can modified as follows:

@ARTICLE{Saetre2010,
  author = {Saetre, Peter and Lundmark, Per and Wang, August and Hansen, Thomas
    and Rasmussen, Henrik B. and Djurovic, Srdjan and Melle, Ingrid and
    Andreassen, Ole A. and Werge, Thomas and Agartz, Ingrid and Hall,
    Hakan and Terenius, Lars and Jonsson, Erik G.},
  title = {The Tryptophan Hydroxylase 1 ({TPH1}) Gene, Schizophrenia Susceptibility,
    and Suicidal Behavior},
  subtitle={A Multi-Centre Case-Control Study and Meta-Analysis},
  journal = {American Journal of Medical Genetics, Part B: Neuropsychiatric Genetics},
  year = {2010},
  volume = {153B},
  pages = {387--396},
}