I have two kids adopted from Kaz, they are 4 and 2 now, adopted at 9mths and 6mths. My daughter, who was 9mths didn't exactly have attachment disorder but issues, she took about a year to fully attach to me and DH, we worked hard at attachment techniques and it paid off.
She's 4 now and fully attached in every way. She is home from preschool sick and spent about 6hrs on my lap yesterday. She does struggle with some minor sensory issues but they don't impact her life and she's learned to mostly deal with them through a few OT sessions. She's very social and smart, she's reading at a first grade level in preschool and is very popular with her friends. She's also a diva with a difficult personality that I admire and find frustrating all at the same time
My 2yr old attached within a few days, I know many will find that hard to believe but at 6mths old he was so little and so dependent on us the difference in the age was really obvious. He is no different than any bio child that I know, although of course I don't have any. DS is a snuggle bug who loves his mommy and daddy and sister more than anything. He's easy going and super athletic for his age and circumstances. He was starting to crawl when we met him, walked at 10mths and ran at 11mths. Could something come up with him later? Sure, but I don't think it would be attachment related.
I agree with the PP that attachment issues are real and not unusual. Some are like my daughter and over time and hard work are fixable, some are more serious. But, I don't think my son is that unusual a case either, although it is difficult to adopt a 6-7mth old, we were very lucky.