the first three rows (they can be in any order):

 AFFECTED = <space delimited diagnostic codes>
 UNAFFECTED = <space delimited diagnostic codes>
 UNKNOWN = <space delimited diagnostic codes>
 
the 4th row:

 Liab = <number of liability classes>

the 5th - (5+Liab-1)'th rows (these Liab rows can be in
any order), for each line, it is like this:

 <space separated diagnostic codes>,
 <F = Female or M = Male or U = not sex-based>,
 <lower and upper age limit>,
 <disease penetrances>

the last row is the disease allele frequency
 

A sample file

AFFECTED = AFF_DEF AFF_PRB  AFF_POS
UNAFFECTED = AFF_NO
UNKNOWN = AFF_UNK
liab = 3
AFF_POS AFF_DEF AFF_PRB, U, 0 30, 0.01 0.01 0.5
AFF_NO AFF_UNK, F, 0 999,  0.014 0.014 0.666
AFF_NO AFF_UNK, M, 0 999,  0.007 0.007 0.333
0.01