Rett Syndrome

Question 1

How many exon she in MECP2?

Answer 1

4

Question 2

What % of females with classic rett have an mecp2 mutation?

Answer 2

80-95%

In 99.5% of cases they are de novo

Question 3

How many reported pathogenic mutations?

Answer 3

~390 recorded in RettBase

Question 4

What exons contain 80% of mutations?

Answer 4

3-4. But less for the preserved speech variant of atypical rett (~50%)

Question 5

What is believed to cause the large deletions of exons 3 and 4 identified in typical and atypical rett ?

Answer 5

Highly repetitive sequences in exon 4 and intron 2 causing unequal recombination

Question 6

What causes 71% of the de novo mutations found in female rett?

Answer 6

De novo mutations in male germ cells

Commonly caused by mutations to CpG dinucleotides ( many c>t)

Question 7

What percentage of typical and atypical rett is caused by large mutations?

Answer 7

30% of classic and 7% of atypical

Question 8

How common are mutations in cons 1 and 2?

Answer 8

Rare in exon 1 and to date none found in exon 2

Question 9

How many domains in mecp2?

Answer 9

3 functional domains and a nuclear localisation domain

Question 10

Where are Missense mutations most commonly found?

Answer 10

In methyl binding domain (mpd) it binds methylated CpGs

Question 11

Where are nonsense mutations most commonly found?

Answer 11

Between MbD and transcription repression domain (trd) - recruits co-repressor complexes that mediate repression or transcription

Question 12

Where are deletions usually found?

Answer 12

In the deletion prone region 336-388 codons

Question 13

What are the 3 functional domains of mecp2?

Answer 13

1) MBD
2) TRD
3) tryptophan-tryptophan binding domain near the c-terminus that binds splicing factors

Question 14

What 3 types of mutations are found in males?

Answer 14

1) mutations found in classic rett
2) mutations inherited from the mother which are not found in females with rett
3) males with deletions of entire genes and neighbouring genes resulting in severe phenotype

Question 15

What is the most common mecp2 syndrome found in males?

Answer 15

Mecp2 duplication syndrome - severe neonatal encephalopathy baby dies within 2 years

Question 16

How many meco2 isoforms are there?

Answer 16

2

Question 17

What isoform is transcribed in the brain?

Answer 17

Mecp2-e1 contains exon1 but alternatively splices out exon 2 encoding a distinct n-terminus 490 aa

Question 18

What isoform is found in fibroblast and lymphocyte cells?

Answer 18

Mecp2-e2 - doesn’t contain exon 1 but contains part of exon 2 486aa

Question 19

Which isoform is more abundant ?

Answer 19

E1, e2 less easily transcribed

Question 20

What is the believed to be the role of mecp2?

Answer 20

A global transcription repressor

May be linked to the regulation of transcription or synaptic activity

Question 21

Phenotype of mutations 3’ to the TRD region ?

Answer 21

Milder phenotype probably due to late truncating protein formed

Question 22

Phenotype of females with missense mutations ?

Answer 22

Significantly milder phenotype than those with nonsense/ frame shift mutations

Question 23

Location of missense and truncating mutations?

Answer 23

Missense predominantly in MBD and truncating in TRD or 3’ end

Question 24

Why are truncating mutations not found in MBD?

Answer 24

May be due to selection against as the phenotype may be too severe

Question 25

Bidirectional sequencing of mecp2 detects what % of classic and atypical rett?

Answer 25

85-90% of classic and 30-40% atypical

Question 26

When should u check primers for snps?

Answer 26

Each time data base is updated

Question 27

Testing strategy

Answer 27

1) pcr conditions same for 2-4 but dif for 1
2) primers tagged and sequencing carried out using abi big dye terminator kit and run on abi 3130
3) data analysed using MS by comparing test and control. Genbank files used and annotated. Rob defined.
4) MLPA kit from MRC holland used.

Question 28

If a pathogenic variant is identified what should u do?

Answer 28

Request parental DNA
Offer testing to all female relatives of pro and
Offer testing to males with possible rett phenotype

Question 29

What is skewed x inactivation?

Answer 29

When by chance more than half of cells have chromosome bearing normal genes

Question 30

How to test for x inactivation?

Answer 30

1) Pcr polymorphic CAG repeat in the first exon of the androgen receptor gene (AR)
2) DNA cut with methylation sensitive restriction enzymes HpaII and CfoI
3) look for quantitative skew eg 75:25

Question 31

What gene can be tested if patient has atypical Rett syndrome? What phenotype is found in all patients with a mutation in this gene?

Answer 31

Cdkl5

. Seizures before 6 months

Question 32

What gene involved in the development of the central nervous system is also a candidate for atypical rett? (Only 1 case)

Answer 32

NTNG1= chromosome 1. 340kb, 10 exons (9 coding)

Question 33

What gene causes congenital form of Rett ( presenting in first few month of life)

Answer 33

FOXG1 (14q13)

Question 34

Phenotype for SLC9A6 mutations

Answer 34

Found in x- linked mental retardation., microcephaly, epilepsy and phenotype mimicking angelman syndrome

Question 35

Frequency of Rett syndrome?

Answer 35

1:10,000 by the age of 12

Question 36

Clinical features of Rett?

Answer 36

• Severe neurodevelopment disorder
• Normal early development followed by loss of fine and gross motor skills
• characteristic stereotypic hand movements