1. Myoclonic Epilepsy with Ragged-Red Fibers
mitochondria
28. MERRF

2. Small Group Discussion 1,2 / 3,4
INDEX
Principles
Physical Finding
Background
disease etiology and incidence
pathogenesis
phenotype and natural history
Management
Inheritance risk
Small Group Discussion 1,2 / 3,4

3. Principles to physical finding
이재일

4. pRINCIPLES
mtDNA mutations
Replicative segregation
Expression threshold
High mutation rate
Accumulation of mutation with age
Heteroplasmy

5. Heteroplasmy
Heteroplasmy is the presence of a mixture of more than one type of an organellar genome (mitochondrial DNA (mtDN A) or plastid DNA) within a cell or individual.

6. Major Phenotypic Features
Age at onset: childhood through adulthood
Myopathy
Dementia
Myoclonic seizures
Ataxia
Deafness

7. Myopathy (근질환)
a neuromuscular disease in which the muscle fibers do not function for any one of many reasons
meaning "lack of order". It is a neurological si gn and symptom consisting of gross incoordi nation of muscle movements.
Ataxia (사지 불능)

8. Major Phenotypic Features
Age at onset: childhood through adulthood
Myopathy
Dementia
Myoclonic seizures
Ataxia
Deafness

9. HISTORY and PHYSICAL FINDINGS
R.S., Male, Age 15
Well developed.
Clinic for myoclonic epilepsy.
EEG(Electroencephalogram) bursts of slow wave and spike complex

10. FAMILY HISTORY [MATERNAL]
Grand Mother
Mother
Pt. R. S. MERRF
Uncle
Aunt G1 G2 G3
Grand mother
deafness, diabetes and renal dysfunction.(80yrs)
Uncle
died of an undiagnosed myophathic disorder.(53yrs)
Aunt
progressive dementia who had presented with ataxia.(37yrs)
R.S.(Pt.)'s sibs and his mother's sibs were carriers of a mtDNA mutation.

11. Examination
Muscle wasting and weakness
Myoclonus
Ataxia

12. Myoclonus
is brief, involuntary twitching of a muscle or a group of muscles.

13. Examination
Muscle wasting and weakness
Myoclonus
Ataxia

14. Initial evaluation
Sensorineural hearing loss
Slow nerve conduction
Mildy elevated blood
Cerebrospinal fluid lactate level

15. Deficient staining for cytochrome oxidase Ragged-red fibers
Muscle biopsy
Abnormal mitochondria
Deficient staining for cytochrome oxidase
Ragged-red fibers

16. Testing mutations within mtDNA
Heteroplsmic mutation (8344G>A, tRNAlys gene)
associated with Myoclonic Epilepsy with Ragged-Red fibers (MERRF)

17. background
장준원

18. Disease Etiology and Incidence
MERRF is caused by mutations within the mtDNA in the tRNAlys gene.
More than 90% of patients have one of three mutations within this gene
8344G>A accounts for 80%
8356T>C and 8363G>A together account for an additional 10%
Inherited maternally
MERRF patients are nearly always heteroplasmic for the mutant mitochondria.
-tRNA lys gene 에 대한 mtDNA에 mutation이 일어나 발생하는 질병.
-8344G>A
-미토콘드리아가 모친에서만 유래하므로 모계를 통해 유전된다.
-일부는 돌연변이가 있고 일부는 없는 미토콘드리아를 가진다 (heteroplasmy)

19. Pathogenesis
Mitochondria generate ATP energy through oxidative phosphorylation.
In MERRF, the activities of Com I and IV are severely reduced.
Expression of the MERRF phenotype ultimately depends on the overall reduction in OXPHOS capacity.
The threshold for expression of a deleterious phenotype depends on the balance between oxidative supply and demand.
-Complex I ,IV는 대부분의 구성물이 미토콘드리아 내에서 생성되므로 가장 심하게 영향을 받는다.
-각각의 미토콘드리아는 여러 개의 mtDNA를 가지고있고, 각각의 세포는 여러 개의 미토콘드리아를 가지고 있기 때문에 세포는 정상 미토콘드리아와 비정상 미토콘드리아를 다양한 비율로 가질수 있게 된다.
-경계점은 나이와 개체, 기관계, 그리고 조직에 따라 다양하다. MERRF 표현형이 발현되느냐 마느냐의 경계점은 정상 mtDNA 유전인자 발현의 효율의 감소나 돌연변이 mtDNA양의 증가에 의해 결정된다.

20. Oxidative Phosphorylation
Fig. OXPHOS takes place in Electron transport chain
Com I (NADH dehydrogenase) accepts fuel from the citric acid cycle in the form of NADH, which donates electrons to the chain. Com II Succinate dehydrogenase) accepts electron from FADH2 and passes them to COM III via cytochrome C.
Com III (cytochrome-c oxidase) Com V (ATP synthase) converts adenosine diphosphate (ADP) to adenosine triphosphate (ATP)

21. Com I to V compose the OXPHOS pathway.
Except for Com II, each complex has some components encoded within the mtDNA and some in the nuclear genome.
The mtDNA encodes 13 of the polypeptides in the OXPHOS complexes as well as 2 rRNAs and 22 tRNAs

22. Pathogenesis
Mitochondria generate ATP energy through oxidative phosphorylation.
In MERRF, the activities of Com I and IV are severely reduced.
Expression of the MERRF phenotype ultimately depends on the overall reduction in OXPHOS capacity.
The threshold for expression of a deleterious phenotype depends on the balance between oxidative supply and demand.
-Complex I ,IV는 대부분의 구성물이 미토콘드리아 내에서 생성되므로 가장 심하게 영향을 받는다.
-각각의 미토콘드리아는 여러 개의 mtDNA를 가지고있고, 각각의 세포는 여러 개의 미토콘드리아를 가지고 있기 때문에 세포는 정상 미토콘드리아와 비정상 미토콘드리아를 다양한 비율로 가질수 있게 된다.
-경계점은 나이와 개체, 기관계, 그리고 조직에 따라 다양하다. MERRF 표현형이 발현되느냐 마느냐의 경계점은 정상 mtDNA 유전인자 발현의 효율의 감소나 돌연변이 mtDNA양의 증가에 의해 결정된다.

23. mtDNA has high mutation rate (10x nDNA)
mtDNA has no intron, random mutations affect coding sequences.
Mitochondrial efficiency declines gradually with age
Increases in the proportion of mutant mtDNA can occur by a combination of inheritance, preferential replication of mutant mtDNA, and selection.
-이 사실은 OXPHOS에서 유래되는 높은 농도의 oxygen free radicals에의 노출, 보호 기능을 가진 histone의 결핍 및 비효율적인 DNA복구 기능에 기인한 결과일수 있다.
-이런 증가된 돌연변이 가능성과 더불어 미토콘드리아의 효율은 성인기를 거치면서 서서히 감소하고, 남아있는 OXPHOS활성도가 감소함에 따라 OXPHOS pathway에서 잘못 발현되는 경우가 증가하게 된다.

24. Both intercellular and intergenerational mtDNA transmission follow the principles of population genetics.
The children of heteroplasmic mothers have widely varying proportions of mtDNA genotypes because of replicative segregation.
As heteroplasmic cells within an individual undergo mitosis, the proportion of mtDNA genotypes in daughter cells changes from that of the parent cell by replicative segregation.
The mtDNA is subject to strong selective pressures because changes in the proportion of mtDNA genotypes affect the cellular phenotype.
-selective pressure는 조직내에서 다양하며 같은 사람의 다른 조직에서 서로 다른 mtDNA 비율을 보일 수 있다.
-그러므로 세포간 또는 세대간의 mtDNA 전달은 모두 집단유전의 원칙을 따른다.
집단유전의 원칙
커다란 개체군에서 유전자를 변화시키는 외부적 힘이 작용하지 않는 한 '우성유전자와 열성유전자의 비율은 세대를 거듭해도 변하지 않고 일정하다'는 것
외부적 힘에는 돌연변이나 이동 등이 있다.

25. Replicative segregation
Random partitioning of mitochondria during expansion of the oogonial population, particularly because of the mitochondrial “genetic bottleneck” that occurs during oogenesis
난조세포수의 확장때 일어나는 미토콘드리아의 무작위 분할
특히 난자발생때 나타나는 미토콘드리아의 “genetic bottleneck” 때문에 일어난다.

26. Population Bottleneck (genetic bottleneck)
an evolutionary event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing
Sudden fall down
Of population
-동물의 개체수가 갑자기 급격히 감소하는 사건.

27. Both intercellular and intergenerational mtDNA transmission follow the principles of population genetics.
The children of heteroplasmic mothers have widely varying proportions of mtDNA genotypes because of replicative segregation.
As heteroplasmic cells within an individual undergo mitosis, the proportion of mtDNA genotypes in daughter cells changes from that of the parent cell by replicative segregation.
The mtDNA is subject to strong selective pressures because changes in the proportion of mtDNA genotypes affect the cellular phenotype.
-selective pressure는 조직내에서 다양하며 같은 사람의 다른 조직에서 서로 다른 mtDNA 비율을 보일 수 있다.
-그러므로 세포간 또는 세대간의 mtDNA 전달은 모두 집단유전의 원칙을 따른다.
집단유전의 원칙
커다란 개체군에서 유전자를 변화시키는 외부적 힘이 작용하지 않는 한 '우성유전자와 열성유전자의 비율은 세대를 거듭해도 변하지 않고 일정하다'는 것
외부적 힘에는 돌연변이나 이동 등이 있다.

28. Phenotype to inheritance risk
조한철

29. Phenotype and Natural history
Classical symp.
Progressive myoclonus
Raggred red fiber
Continuous symp.
Abnormal brainstem reaction,
Deafness /nephric failure, diabetes
Ataxia / cardiac myopathy
dementia
Phenotype
Relation with mutant mtDNA ratio in muscular tissue must be considered with Pt.'s age
OXPHOS capacity declines below organ expression threshold with age
Clinical aspect variable in form and grade, cannot regulate progress easily. Some MERRF cases are not with Ragged-red fibers in muscular biopsy. So mtDNA test is preferred, and muscular biopsy is assistant.

30. No useful treatment. Management
Treatment must be temporarily expedient to symptoms.
Mostly prescribes vitamins to optimize OXPH OS activity.

31. mtDNA inherits from mother.
Inheritance Risk
Children of
Affected male : no risk
Affected female : risky
mtDNA inherits from mother.

32. 2 major problems in blood testing in at-risk family
Inheritance Risk
2 major problems in blood testing in at-risk family
Because of replicative segregation and tissue selection, the mutation may not be detectable in blood.
Because of Replicative segregation, (+) result inform us neither the proportion of mutant mtDNA nor the expected severity of disease.

33. Small group discussion 1, 2
이지원

34. Questions for small group discussion
1. How does a mutant mtDNA molecule, arising de novo in a cell with hundreds of normal molecules, become such a significant fraction of the total that energy-generating capacity is compromised and symptoms develop?
어떻게 수많은 정상의 molcule과 함께 발생한 mutant mtDNA mocule이 에너지 생성 능력이 손상되거나 증상 이 유발되는 것처럼 전체에 있어서 중요한 영역이 될 수 있는가?

35. Questions for small group discussion 1

36. Questions for small group discussion
2. How could mitochondrial mutations affecting oxidative phosphorylation accelerate the mutation rate of mtDNA?
Oxidative phosphorylation에 영향을 주는 미토콘드리 아 돌연변이가 어떻게 mtDNA의 돌연변이 비율을 촉진 시킬 수 있는가?

37. Questions for small group discussion 2

38. Small group discussion 3, 4
이정택

39. Questions for small group discussion
3. how could mitochondrial mutations affecting oxidative phosphorylation accelerate aging?
산화적 인산화에 영향을 주는 미토콘드리아 변이는 어 떻게 노화에 영향을 주는가?

40. Questions for small group discussion 3

41. Questions for small group discussion
4. In the fetus, oxygen tenion is low and the most energy is derived from glycolysis. How could this observation affect the prenatal expression of deleterious oxidative phosphorylation mutations?
태아기엔 산소분압이 낮고 대부분의 에너지는 해당과 정에 의해 얻어진다. 이러한 상황이 어떻게 유해한 산 화적 인산화 이상의 태아적 표현형에 영향을 미칠까?

42. Questions for small group discussion 4

43. credits
7조 이재일 이정택 이지원 장준원 정신석 조한철 진호
College of medicine, Dankook Univ.