myotonic dystrophy

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MYOTONIC DYSTROPHY • It is a chronic, slowly progressing , highly variable inherited multi systemic disease. • There are 2 main types of myotonic dystrophy • A)myotonic dystrophy-1 or steinert disease • B)myotonic dystrophy-2 or proximal myotonic myopathy(PROMM) • Myotonic dystrophy-1 • It is also known as steinert disease • People with this type have – • An adult onset form / juvenile onset MMD1. • A severe congenital form. • A milder form. • Myotonic dystrophy-2 • It is also known as proximal myotonic myopathy (PROMM) • It is rarer and generally manifests with milder signs than myotonic dystrophy-1

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Page 1: myotonic dystrophy

MYOTONIC DYSTROPHY• It is a chronic, slowly progressing , highly variable inherited multi systemic disease.• There are 2 main types of myotonic dystrophy• A)myotonic dystrophy-1 or steinert disease• B)myotonic dystrophy-2 or proximal myotonic myopathy(PROMM)• Myotonic dystrophy-1• It is also known as steinert disease• People with this type have –• An adult onset form / juvenile onset MMD1.• A severe congenital form.• A milder form.• Myotonic dystrophy-2• It is also known as proximal myotonic myopathy (PROMM)• It is rarer and generally manifests with milder signs than myotonic dystrophy-1

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Myotonic dystrophy subtypes-

Type - gene - repeat - anticipation - severityDM 1 DMPK CTG YES MODERATE- SEVERE.DM 2 ZNF9 CCTG MINIMAL/ MILD- NONE MODERATE. MYOTONIC DYSTROPHY TYPE-1 It is inherited in an autosomal dominant pattern which is

caused by a change or mutation in a specific gene , called myotonic dystrophy protein kinase(DMPK)gene , which is essential for normal muscle and body function.

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• Description - symptoms - recognition - lifespan• mild a)cataracts adult hood normal• b)mild myotonia• c)balding• d)may have diabates

Classical a)weaknass childhood to b)myotonia early adulthod may be c)cataracts shortened. d)balding e)irregular heart beat f)may have diabetes

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• Congenital a)severe weakness birth to shortened• b)myotonia childhood • c)breathing difficulties• d)often mild to • moderate mental retardation• adult onset myotonic dystrophy-• It affects multiple organs , systems.• It is a genetic disease which is caused due to the expanded section of DNA

on chromosome 19.• The adult onset form sometimes called “classic myotonic dystrophy “ and

thought to be the most common type-has its onset in late adolesence or young adulthood.

• It affects a number of body systems , although there is a wide range of severity.

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the muscle related symptoms include-a) Myotonia for which the disease is named ,and weakness,particularly of

the face, neck and limb muscles that are furthest from the center of the body (the distal muscles),such as the forearms , hands , lower legs ,and feet . overtime , all limb muscles can become weak.

Among the most severe forms of MMD1 are- a)weakness of the breathing and swallowing muscles and dysfunction of the heart muscles , particularly the tissue in the heart that conducts electrical impulses from one part of the heart to another.

b)The so-called “smooth muscles of the gastro intestinal tract can be affected,causing diarrhoea,constipation and abdominal pain.c)Other smooth muscles that line the hollow organs iof the body ,such as uterus, and gall bladder ,can be affected as well ,leading to obsteric complications and gall stones.

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d)the lenses in the eyes almost always develop cataracts , which can be surgically removed when they interfere with vision . The cataracts are distinctive and have been described as resembling christmas tree lights .

e)And then there are effects on brain ,causing a range of symptoms, including learning disabilities,difficulties with decision making,and what some psychologists have called an avoidant or apathetic personality type .

f)Excessive day time sleepness and chronic fatigue are among the most puzzling and troublesome of MMD1symptoms , and their origin appears to be complex and probably related to the effects of disease on the brain , limb muscles , respiratory systems and heart and perhaps to altered levela of testosterone and insulin.

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• Congenital MMD1-• The most serious form of MMD1 .• Congenital – onset – MMD1 – makes it self known at birth.• Babies born with congenital MMD1 have very weak muscles and lack of

muscle tone ( hypotonia ) .• They appear floppy , and have trouble breathing , sucking and swallowing .• There are always abnormalities in cognitive function , although

intelligence can be in the normal range . • Speech and having difficulties often occur and weakness of the eye

muscles can cause vision problems . (cataracts aren’t a feature of congenital MMD during early childhood , but develop later as they do in adult onset MMD1 ).

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• In the past many babies with congenital onset MMD didn’t survive and death in the early months isn’t uncommon even now but with modern new born intensive care units , these babies have much better chance of survival .

• They often need help of developing alternate means of communicating , so they can overcome the speech and writing difficulties caused by mouth , tongue and hand weakness .

• Causes-• In DM1 affected gene is called DMPK ,which codes for myotonic dystrophy

protein kinase (DMPK) .• DMPK is a protein expressed predominently in skeletal muscle .• The gene is located on the long arm of chromosome 19.

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• In DM1 there is an expansion of cytosine-thymine-guanine (CTG)triplet repeat in DMPK gene .

• These CTG repeats are normal components of a gene known as DMPK , but the usuall number of repeats ranges from 3-37.

• In people with MMD1 , the CTG sequence is repeated atleast 50 times . • At the lower end of the expansion range (about 50-80 repeats),symptoms

may be very mild or non existent .• Cataracts are common but they often don’t lead to an MMD diagnosis• The classic disease (for adult onset MMD1)is often between 100-500

repeats.• Children born with the congenital onset form can have 1000’s of CTG


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• Myotonic dystrophy is inherited in an autosomal dominant pattern .this means each son/daughter of a person with DM has a 1 in 2 , or 50% chance of inheriting the condition .

• DM affects males and females equally. • It is caused by a change or mutation in specific gene ,called the myotonic

dystrophy protein kinase (DMPK ) gene which is essential for normal muscle and body function .

• Every person has 23 pairs of chromosomes ,which contain two copies of each gene .the DMPK GENE is located on chromosome 19 .

• It is normal to have between 5-37 repeats in both copies of the DMPK gene.

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Repeat size and severity of symptoms in DM.

Description • Normal range• No symptoms• (children at risk )• Mild• Classical • Congenital

CTG repeat size• 5-37• 38-49

• 50-150• About 100 to 1000.• About 1000 and greater.

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Cardiac care in MMD • In MMD scarring of conduction system of the heart may prevent signals

from the upper chambers (atria)from being transmitted to the lower chambers (ventricals),so that people with the disease4 may be un aware of dangerously fast atrial heart rhythms/arrhythmias.

• Unfortunately ,the first symptom they experience can be a stroke , instead of rapid heart rate.

• Arrhythmias that are too slow sometimes require a pace maker that delivers regularly timed electrical impulses to bring the heart rate up to normal.

• When heart rhythm is too fast ,an implantable defibrillator can deliver an electrical shock to restore a normal heart rhythm . (these are sometimes called implantable cardioverter – defibrillators or ICDS


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people with MMD1 develop abnormalities in the heart tissue responsible for the pumping of blood , a condition known as cardiomyopathy-Actual heat failure (partial / complete failure of the pumping mechanism ) is uncommon in people with MMD. Symptoms-A)”Watch out for palpitations “(the feeling that the heart is beating hard , fast and irregularly.)B)Severe light headedness , fainting , or significant shortness of breath.C)Patients with advanced myotonic dystrophy have respiratory issues. therefore some of those symptoms , such as shortness of breath , might not necessarily reflect cardiac problems .

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• D)presentation of symptoms and signs varies considerably by form (DM1/DM2).

• DM1 symptoms for DM2 include problems with • -executive function • -hypersomnia (mental disorder)• -cortical cataract with blue dot appearance • -a posterior sub capsular cataract• -intellectual disability.• Treatment and manifestations-• Use of ankle foot orthoses , wheel chairs , or other assistive devices• Treatment for hypothyroidism. • Management of pain.

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• Consultation with a cardiologist for symptoms (or) ECG evidence for arrhythmia.

• Removal of cataracts if vision is impaired.• Harmone replacement therapy for males with hypogonadism.• Surgical excision of” pilomatrixoma”(benign skin tumor derived from the

hair matrix.)• Surveillance-• Annual ECG / 24 hours holter monitering.• annual measurement of fasting serum glucose concentration and

glycosylated haemoglobin concentration .• Eye examination for every two years .• Attention to nutritional status.

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• Agents and circumstances to avoid-• Cholestrol lowering medications (i.e.,statins ) which can cause muscle pain

and weakness ; anesthetic agent vecuronium.• • PRINCIPLE-• Polymerase chain reaction• The polymerase chain reaction is a scientific technique in molecular biology

to amplify a single or a few copies of a piece of DNA across several orders of magnitude , generating thousands to millions of copies of a particular DNA sequence .

• It was developed in 1984 by the American biochemist , kary mullis . Mullis received the Nobel prize and the japan prize for developing PCR in 1993 .

• PCR is now common and often indispencible technique used in medical and biological research labs for a variety of applications

• The PCR reaction is a powerful technique that has rapidly become one of the most widely used techniques in molecular biology ,because it is quick , inexpensive and simple .

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• This technique amplifies specific DNA fragments from minute quantities of source DNA material , even when that source DNA is of relatively poor quantity.

• BASIC CONCEPT OF PCR-• The basic concept of PCR is the name implies it is a chain reaction.• “one DNA molecule is used t produce two copies , then four , then eight ,

and so fourth.”• This continuous doubling is accomplished by specific proteins known as

polymerases , enzymes that are able to string together individual DNA building blocks to form long molecular strands . To do their job polymerases require supply of DNA building blocks , i.e., the nucleotides consisting of the 4 bases – adenine (A) , guanine (G) , thymine (T) , cytosine (c) .

• They also need a small fragment of DNA , known as primers , to which they attach the building blocks as well as a longer DNA molecule to serve as a template for constructing the new strand .

• It these two ingredients are supplied , the enzymes will construct exact copies of the templates.

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• PCR is a method used to acquire many copies of any particular strand of nucleic acids . It’s a means of selectively amplifying a particular segment of DNA .

• The segment may represent a small part of a large and complex mixture of DNA’S . eg; a specific exon of a human gene . It can be thought of as a molecular photocopier .

• PCR can amplify a usable amount of DNA (visible by electrophoresis) in ~2hours.

• The template DNA need not be highly purified – a boiled bacterial colony.• The PCR product can be digested with restriction enzymes , sequenced or

cloned .• PCR can amplify a single DNA molecule .• Eg; from a single sperm. The PCR relies on the ability of DNA– copying

enzymes to remain stable at high temperatures .

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• There are three main steps in PCR technique:-• Step 1 :- denaturation of DNA • the DNA is denatured at high temperatures (from 90-97c)• Step 2 :- annealing• primers anneal to the DNA template strands to prime

• extensions.(from 45-60c)• Step 3 :- polymerization• extension occurs at the end of the annealed primers to

create a complementary copy strand of DNA . This effectively doubles the DNA quantity .(from 72-75c)

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In PCR cycle to amplify the segment of DNA using PCR :-a)The sample is first heated so that the DNA gets denatures , or separates in to two pieces of single stranded DNA .b)Next an enzyme called “taq polymerase synthesizes-builds-two new strands of DNA using the original strands as templates . This process results in duplication of the original DNA . With each of the new molecules containing one odd and one new strand of DNA .c)Then each of those strands can be used to create two new copies and so on .d)The annealing phase happens at low temperature , 50-60c . This allows the primers to hybridize their respective complementary template strands .e)The newly formed DNA strand of primer attached to template is then used to create identical copies of the original template strands desired.f)”tag polymerase adds available nucleotides to the end of the annealed primers . The extension of the primers by taq polymerase occurs at approx. 72c for 2-5 min.g)DNA polymerase cannot be used to elongate the primers as one would expect because it is not stable at high temperatures required for PCR.

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• h)After 25-30 cycles , who ever is performing the PCR process on a sample of DNA will have plenty of copies of the original DNA sampler to conduct experimentation.

• I)assuming the maximum amount of the time for each step , 30 cycles would take only 5 hours to complete .

• As the process of denaturation , annealing , and polymerase extension is continued ,

• -the primers repeatedly bind to both the original DNA template • and complementary sites in the newly synthesized strands • and are extended to produce new copies of DNA .• -the temperature at which DNA gets denatured is called • as annealing temperature (tm) which can be • mathematically represented as –• tm = 4(G+C) + 2(A+T) .• -the taq polymerase can with stand repeated heating to 94c and

so each time the mixture is cooled to allow the oligonucleotide primers to bind the catalyst for the extension is already present.

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• -after last cycle , samples are usually incubated at 72c for 5min to fill in the protruding ends of newly synthesized PCR products .

• -to ensure success , care should be taken both in preparing the reaction mixture and setting up the cyclic conditions.

-increasing the cycle number above ~35 has the little positive effect because the plateau occurs when there agents are depleted ; accumulated .• -the specificity of amplification depends on the extent to which the

primers can recognize and bind to sequence other than the intended target DNA sequence .

• -the end result is an exponential increase in the total number of DNA fragments that include the sequences between the PCR primers , which are finally represented at a theoretical abundance on 2n , where n is the number of cycles .

• The primers which are used to detect myotonic dystrophy in PCR are-• forward primer - GAAGGGTCCTTCTAGCCGGGAA. reverse primer – CAGAGCAGGGCGTCATGCACA.

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Steps of cycler1)Initial denaturation




5)Final extension

Temperatures and timings for each cycleTemperature-95 degrees

Time-5 minutes.

Temperature – 95 degreesTime- 1 minute.

Temperature-57 degreesTime – 1 minute.

Temperature – 72 degreesTime – 15 seconds.

Temperature – 72 degreesTime – 5 minutes.