Behavior in Four Chromosomal Syndromes

On the Trisomy 9 Website, run by the mother of a little boy with partial trisomy 9p, there is a survey. A few years ago, she used to provide the full data set of the survey as well as the results. Back then, I downloaded a copy of it, and now that I have access to SPSS, I've decided to analyze the results myself.

I'm focusing on the subsection regarding behavior ('habits'), because I'm fascinated by behavioral phenotypes. There are many different kids with different conditions described in the survey, but I'll focus on the four most common syndromes - trisomy 13, trisomy 18, partial trisomy 9p, and mosaic trisomy 9. I took all the kids within those four groups (11 with trisomy 13, 16 with trisomy 18, 25 with trisomy 9p and 8 with mosaic trisomy 9) and analyzed their survey results for behavior.

Factor Analysis

The first thing I did was to run a factor analysis (well, actually, the first thing I did was to recode 'yes' as 2 and 'no' as 1, then I did the factor analysis). I don't really know factor analyses that well, so I may have screwed up stuff. If you know enough about factor analysis to spot a mistake I made, let me know.

I found 10 factors. Here they are, with correlations greater than .3 listed:

• factor 1: chews on toys (.696), dances (.643), chews on clothes (.588), touches everything (.573), stubborn (.561), tantrums (.550), throws head back (.543), throws objects (.503), shows no fear of falling (.438), bites self (.436), tenacious (.432), rubs hand across face (.411), great memory (.400), kicks feet (.381), loves mirrors (.349), affectionate (.325), must hold something (.307) and loves baths (.303)
• factor 2: great memory (-.714), rocks/shakes head (.663), hates eating (.636), kicks feet (.536), throws head back (.520), sucks finger/thumb (.477), dances (-.460), loves eating (-.449), rubs hand across face (.411), drools (.384), very happy (-.378), tenacious (-.365), stubborn (-.353) and must hold something (-.346)
• factor 3: drools (.608), sucks on finger/thumb (.517), loves music (.445), very happy (.444), loves eating (.430), socializes (.405), stubborn (-.399), bites self (.346), kicks his/her feet (-.342), throws objects (-.339), chews on clothes (.316), tantrums (-.313) and rocks/shakes head (.312)
• factor 4: very happy (.598), dislike solitude (.446), loves mirrors (.441), throws objects (.435), rubs hand across face (-.407), tenacious (-.382), grumpy (-.362), socializes (.352), loves baths (.326), throws head back (-.322) and touches everything (.321)
• factor 5: high pain threshold (.697), no fear of falling (.485), loves mirror (-.422), grumpy (.343), loves music (-.340), tenacious (.322), socializes (.314) and bites self (-.302)
• factor 6: loves music (-.589), bangs head (.528), tantrums (.384), touches everything (.363), hates eating (-.350), no fear of falling (-.330), loves eating (.314) and high pain threshold (-.311)
• factor 7: affectionate (.617), loves baths (-.608), grumpy (.433), dislikes being alone (.380) and socializes (.331)
• factor 8: tenacious (.428), drools (.387), touches everything (-.380), grumpy (-.312), throws head back (.303) and tantrums (.302)
• factor 9: bangs head (-.590), dislikes solitude (.462), loves mirrors (-.336) and affectionate (-.328)
• factor 10: loves mirrors (-.466), grumpy (-.408), must hold something (.394) and rubs hand across face (-.302)

Hard to say what most of those factors mean, though I'm guessing that factor 1 is related to hyperactivity, factor 3 might be hyposensitivity and factor 4 is probably cheerfulness.

Anyway, I was interested in two main questions: do children with different syndromes behave differently, and is there an age-based difference in behavior? (The kids ranged from newborn to 30 years old, with no significant difference in age between syndromes.)

Syndrome differences

I ran an ANOVA for each factor related to syndrome. The ANOVA indicated that most of the factors weren't significantly associated with syndrome category, but factor 2 was (p=.001). On the post-hoc tests (Tukey HSD, Scheffe and Bonferroni), this turned out to be due to a significant difference between trisomy 18 and trisomy 9p. Trisomy 18 scored the highest on this factor and trisomy 9p scored the lowest, with the other two in between.

I then ran ANOVAs on the specific behaviors with a loading of at least .3 on factor 2, and found significant effects for 'rocks/shakes head' (p>.001), 'must hold something' (p=.026), 'dances' (p=.025), 'stubborn' (p>.001), 'tenacious' (p=.031) and 'great memory' (p=.002). The post-hoc tests (same as above), showed the following:

• rocks/shakes head: T-13 > T-9p, T-9mosaic; T-18 > T-9p - so trisomy 13 kids were most likely to do this behavior, followed by trisomy 18 kids, then mosaic trisomy 9 and lastly trisomy 9p kids
• must hold something: oddly enough, no differences were significant, but trisomy 9p was approaching significance with all three other groups. So, they might be less likely to engage in this behavior than the other three groups*
• dances: T-9p > T-18 - partial trisomy 9p kids were more likely to dance than trisomy 18 kids
• stubborn: T-13, T-9p, T-9mosaic > T-18 - trisomy 18 kids were significantly less stubborn than the other three groups, who didn't differ from each other
• tenacious: T-9p > T-18 - partial trisomy 9p kids were more tenacious than trisomy 18 kids
• great memory: T-9p > T-18 - partial trisomy 9p kids seemed to have better memory skills than trisomy 18 kids

Age differences

This was trickier, since there were so many individual values for age. Mean age was 7.36 years, with a standard deviation of 8.165 years. I got it to tell me the 20th (2 years), 40th (3 years), 60th (5 years) and 80th (13 years) percentile, and used those to generate a categorical variable for age - <2.5 years, 2.5-3 years, 3-5 years, 5-13 years and >13 years.

I then ran an ANOVA on the different factors with age. Like the trisomy ANOVA, this one found that only factor 2 (p=.011) showed a significant correlation. The post-hoc tests found that 2.5-3 year olds scored significantly higher (p=.046) on factor 2 than >13 year olds did. (The plot of means shows high scores for the two youngest groups and a steady decrease for the three older groups.)

I then ran ANOVAs on the specific behaviors with a loading of at least .3 on factor 2, and found significant effects for 'throws head back' (p>.001), 'hates eating' (p=.006) and 'rubs hand across face' (p=.022). The post-hoc tests showed the following:

• throws head back: under 2.5 > 5-13, over 13 - this behavior was most common in children under 2, and uncommon in kids 5 or over.
• hates eating: 2.5-3 > under 2.5, 3-5, 5-13, over 13 - this behavior peaked around 2.5-3 years
• rubs hand across face: under 2.5 > 5-13 - this behavior was common in very young children, rare in 5-13 year olds, and moderately common both in 3-5 year olds and over 13 year olds.

It's interesting that, though both age and trisomy were related to factor 2, they were related to different behaviors within this factor. Unfortunately, I haven't figured out how to do a two-way ANOVA in SPSS yet, so I don't know if different trisomies show a different age-related pattern.

Note

I posted a previous blog entry regarding my adventures with SPSS, where I tested whether wheelchair bowling is easier than regular bowling. I have recently corrected a mistake I made in that post - larger sample sizes should have smaller standard deviations, not larger.

　
* It spat out an error message saying "The group sizes are unequal. The harmonic mean of the group sizes is used. Type I error levels are not guaranteed." Type 1 errors are finding something when nothing is there, so that might explain why the ANOVA claimed a significant difference that the post-hoc tests failed to confirm.