how to transpose this data id variable is mg and var variables is remaining all

[Chiranjeevi]

data a;
input age sex$ race$ mg$;
cards;
12 m as 10mg
13 f ot 5mg
10 m us 10mg
14 no as 5mg
10 m ot 9mg
;

[Kurt_Bremser]

Please post an example of your expected output.