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}
\MakeSentenceCase
down-cases all letters after the first one. This hasn't changed since 1.7. If you want to keep the first word after colons capitalized, wrap it in braces:Behavior: {A}
. – Audrey Jan 17 '13 at 1:32