表格：制作表格导致空白页

Question

我制作了一个简单的表格，但我发现它会导致文本向下移动并留下很大的空间。这是为什么？有人能告诉我如何修复它吗？

\documentclass{article}


\usepackage{ragged2e}
\usepackage{tabularx, makecell}
\setlength{\extrarowheight}{2pt}
\setlength{\tabcolsep}{3pt}%

\begin{document}


\begin{center}
  \begin{tabular}{ l  | l }
    \hline
    Symbols& Description\\ \hline
    N& The number of SNPs \\ \hline
    n& The number of patients \\ \hline
   X_i&$i$th SNP \\ \hline
   Y&the endpoint  \\\hline
   \beta_i&Effect size for$i$th SNP   \\\hline
   p_{i+}&The probability $X_i=1$ given $Y =+1$ \\\hline
   p_{i-}&The probability $X_i=1 $given $Y =-1$ \\\hline
   n_{+}&The number of patients experience toxicity \\\hline
   n_{-}&The number of patients do not experience toxicity \\\hline
   Z_{i+}&The number of patient has a major allele for $i$th SNP given that patient experience toxicity \\\hline
   Z_{i-}& \makecell{The number of patient has a minor allele for $i$th SNP given that patient do not experience toxicity} \\\hline}
    \hline
    \caption{Summary of notations}
  \end{tabular}
 \end{center}
\end{document}