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MYOTONIC DYSTROPHYIt is a chronic, slowly progressing , highly variable inherited multi systemic disease.There are 2 main types of myotonic dystrophyA)myotonic dystrophy-1 or steinert diseaseB)myotonic dystrophy-2 or proximal myotonic myopathy(PROMM)Myotonic dystrophy-1It is also known as steinert diseasePeople with this type have An adult onset form / juvenile onset MMD1.A severe congenital form.A milder form.Myotonic dystrophy-2It is also known as proximal myotonic myopathy (PROMM)It is rarer and generally manifests with milder signs than myotonic dystrophy-1
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.
RANGE OF SYMPTOMS IN MYOTONIC DYSTROPHYDescription - 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
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.
the muscle related symptoms include-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.
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.
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 arent a feature of congenital MMD during early childhood , but develop later as they do in adult onset MMD1 ).
In the past many babies with congenital onset MMD didnt survive and death in the early months isnt 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.
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 dont lead to an MMD diagnosisThe classic disease (for adult onset MMD1)is often between 100-500 repeats.Children born with the congenital onset form can have 1000s of CTG repeats.
INHERITENCE OF MYOTONIC DYSTROPHY (DM) 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.
Repeat size and severity of symptoms in DM.Description Normal rangeNo symptoms(children at risk )MildClassical Congenital CTG repeat size5-3738-49
50-150About 100 to 1000.About 1000 and greater.
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.
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 .
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 devicesTreatment for hypothyroidism. Management of pain.
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.