Hello all,

             I am currently looking at an MCMCglmm model as follows:


             m = MCMCglmm(ASD_spectrum ~ Diagnosis + brain_volume_1 *
brain_volume_2 + age + Diagnosis*age + Gender,

random=~idh(sqrt(Combined_Symptoms_inatt_plus_hyper)):units,
                                          rcov=~idh(scanner):units,
                                          data=dat)



It is a study of the comorbidity of two disorders (ADHD and autism). I have
subjects with ADHD, unaffected siblings of ADHD subjects, and controls.
Thus, there are three experimental groups within "Diagnosis".


I have the volumes of particular structures in the brain. These are the
fixed factors brain_volume_1 and brain_volume_2. I am interested to know
their relationship with a scale of autistic traits (not ADHD traits) within
all experimental groups.


In the model, I control for differences with ADHD symptoms with:


            random=~idh(sqrt(Combined_Symptoms_inatt_plus_hyper)):units


The brain volumes were acquired with two different scanners, and that is
taken into account with:
            rcov=~idh(scanner):units,


I would now like to control for familial relatedness and am unsure how to
add this into the model. All subjects within the "unaffected sibling" group
obviously have either a brother or sister present in the "ADHD" group.
There are also subjects within the "ADHD" group that have either a brother
or a sister with ADHD. And there are subjects within the "control" group
that have either a brother or sister that are also controls.

            Could anyone advise on the best way to take this familial
relatedness into account within the framework of the model above.

            Thanks in advance for any suggestions.

            As ever; Larry

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