's CHD7 results

[Guest guest]

Simon and others,

I’m a bit behind in getting to this, but here goes:

Seema Lalani did a really nice job of illustrating the

different types of mutations. I’ll see if I can duplicate

something like it here.

DNA is made up of four different bases. These bases are

read in triplets – like 3-letter words. Each triplet is

called a codon. Each codon codes for either

1) Start (i.e. the gene begins here) – I’ll call that

SRT

2) Stop (the gene stops here) I’ll call it STP

3) One of the 20 amino acids (amino acids make up proteins)

4) Nothing (nonsense – will most likely be interpreted as

“stop”)

I’ll use letters instead of bases, and I’m ignoring that

there are only 4 bases (I’m not creative enough to make

words from just A,T,G and C).

Say you have a DNA sequence of SRTDOGANDCATSATANDRANSTP

If you break it down into triplet, it becomes:

SRT DOG AND CAT SAT AND RAN STP – it starts, has a

sentence, then stops.

Now for mutations:

A) Frame shift – if you delete (or add) one letter (here

" D”), you shift the reading frame:

SRT DOG ANC ATS ATA NDR ANS TP – now it doesn’t make

sense

Substitution – if you just change one letter, it might

mess it up, or it might still make sense

SRT DOG AND RAT SAT AND RAN STP – this still makes sense,

but it is different. It might be a polymorphism (change

that doesn’t cause a problem) or one that changes

something critical

SRT DOG AND CAN SAT PND RAN STP – this one does not make

sense – it is a missense mutation

Regarding the rest of ’s mutation – “3’ and

exon” refer to where along the gene the mutation has taken

place. So far, we haven’t seen any correlation between

type or place of mutation and either type or severity of

features of CHARGE

Meg

Meg Hefner, M.S.

Genetic Counselor

St. Louis, MO

hefnerma@... meg@...