What are the other Names for this Condition? (Also known as/Synonyms)

• Autosomal Dominant Limb-Girdle Muscular Dystrophy Type 1B
• LGMD1B (Limb-Girdle Muscular Dystrophy Type 1B)
• Proximal Muscular Dystrophy Type 1B

What is Limb-Girdle Muscular Dystrophy Type 1B? (Definition/Background Information)

• Limb-Girdle Muscular Dystrophy Type 1B (LGMD1B) is one of many types of limb-girdle muscular dystrophy. These diseases affect the voluntary muscles, which are the muscles that are moved on purpose, such as the arms, legs, fingers, toes, and facial muscles.
• Specifically, Limb-Girdle Muscular Dystrophy Type 1B causes muscle weakness in the lower limbs. The muscle weakness typically affects the muscles closest to the center of the body (proximal muscles) such as the upper legs. The disease is progressive, leading to a loss of muscle strength and bulk over a number of years
• Limb-Girdle Muscular Dystrophy Type 1B is caused by mutations (changes) to the LMNA gene. The disease is inherited in an autosomal dominant manner
• A diagnosis of Limb-Girdle Muscular Dystrophy Type 1B is suspected in people who have signs and symptoms consistent with the disease, and the diagnosis can be confirmed with laboratory tests
• While there are no treatments that can reverse the muscle weakness associated with the disease, supportive treatment can decrease the complications

(Source: Limb-Girdle Muscular Dystrophy Type 1B; Genetic and Rare Diseases Information Center (GARD) of National Center for Advancing Translational Sciences (NCATS), USA.)

Who gets Limb-Girdle Muscular Dystrophy Type 1B? (Age and Sex Distribution)

• Limb-Girdle Muscular Dystrophy Type 1B is a rare congenital disorder, occurring in 1-9 individuals among a million
• The presentation of symptoms may occur in childhood or adolescence
• Both males and females may be affected
• Worldwide, individuals of all racial and ethnic groups may be affected

What are the Risk Factors for Limb-Girdle Muscular Dystrophy Type 1B? (Predisposing Factors)

• A positive family history may be an important risk factor, since Limb-Girdle Muscular Dystrophy Type 1B can be inherited
• Currently, no other risk factors have been clearly identified for LGMD1B

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Limb-Girdle Muscular Dystrophy Type 1B? (Etiology)

Limb-Girdle Muscular Dystrophy Type 1B is caused by mutations in the LMNA gene.

• Specifically, LMNA provides instructions to make a protein that is located in the nuclear envelope, which surrounds the nucleus and this protein is responsible for providing stability and strength to the cells
• Limb-Girdle Muscular Dystrophy Type 1B is inherited in an autosomal dominant manner. 
• LMNA gene mutation(s) causing the condition can also occur de novo, and in such cases, an affected individual would not have a family history of the condition

(Source: Limb-Girdle Muscular Dystrophy Type 1B; Genetic and Rare Diseases Information Center (GARD) of National Center for Advancing Translational Sciences (NCATS), USA.)

Autosomal dominant inheritance: Autosomal dominant conditions are traits or disorders that are present when only one copy of the mutation is inherited on a non-sex chromosome. In these types of conditions, the individual has one normal copy and one mutant copy of the gene. The abnormal gene dominates, masking the effects of the correctly function gene. If an individual has an autosomal dominant condition, the chance of passing the abnormal gene on to their offspring is 50%. Children, who do not inherit the abnormal gene, will not develop the condition or pass it on to their offspring.

What are the Signs and Symptoms of Limb-Girdle Muscular Dystrophy Type 1B?

The signs and symptoms of Limb-Girdle Muscular Dystrophy Type 1B may include:

• Muscle weakness, especially in the lower limbs. The muscle weakness typically affects the muscles closest to the center of the body (proximal muscles) such as the upper legs
• Unusual walking gait and difficulty running or using the stairs
• Difficulty straightening the elbows (elbow contracture) 
• Abnormal atrioventricular conduction
• Bradycardia
• Difficulty climbing stairs
• Difficulty walking
• Dilated cardiomyopathy
• Elevated serum creatine phosphokinase
• EMG: Myopathic abnormalities
• Flexion contracture
• Muscular dystrophy
• Pelvic girdle amyotrophy
• Pelvic girdle muscle weakness
• Primary atrial arrhythmia
• Shoulder girdle muscle weakness

(Source: Limb-Girdle Muscular Dystrophy Type 1B; Genetic and Rare Diseases Information Center (GARD) of National Center for Advancing Translational Sciences (NCATS), USA.)

How is Limb-Girdle Muscular Dystrophy Type 1B Diagnosed?

Limb-Girdle Muscular Dystrophy Type 1B is diagnosed on the basis of the following information:

• Complete physical examination
• Thorough medical history evaluation
• Assessment of signs and symptoms
• Laboratory tests, which may include:
  • Electromyography (EMG)
  • Creatine-kinase levels
• Imaging of the heart, such as an echocardiogram
• Biopsy of the affected muscle
• Molecular genetic testing to check for or confirm causative gene mutation(s)

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Limb-Girdle Muscular Dystrophy Type 1B?

The complications of Limb-Girdle Muscular Dystrophy Type 1B may include:

• Progressive weakening of proximal muscles 
• Loss of bulk over a period of time
• Abnormal heart function
• Cardiac arrest

Complications may occur with or without treatment, and in some cases, due to treatment also.

How is Limb-Girdle Muscular Dystrophy Type 1B Treated?

There is no cure for Limb-Girdle Muscular Dystrophy Type 1B, since it is a genetic condition. The treatment is usually given to manage the signs and symptoms and any complication that develops. These may include:

• Avoiding obesity through nutrition and exercise regimens
• Physiotherapy
• Mechanical aids for mobility, which may include the use of canes, walkers, and wheelchairs
• Pacemaker implantation, if necessary
• Heart transplantation in individuals with a damaged heart

How can Limb-Girdle Muscular Dystrophy Type 1B be Prevented?

Currently, Limb-Girdle Muscular Dystrophy Type 1B may not be preventable, since it is a genetic disorder.

• Genetic testing of the expecting parents (and related family members) and prenatal diagnosis (molecular testing of the fetus during pregnancy) may help in understanding the risks better during pregnancy
• If there is a family history of the condition, then genetic counseling will help assess risks, before planning for a child
• Active research is currently being performed to explore the possibilities for treatment and prevention of inherited and acquired genetic disorders

Regular medical screening at periodic intervals with tests and physical examinations are recommended.

What is the Prognosis of Limb-Girdle Muscular Dystrophy Type 1B? (Outcomes/Resolutions)

• The prognosis of Limb-Girdle Muscular Dystrophy Type 1B is dependent upon the severity of the signs and symptoms and associated complications, if any
• This condition is progressive, and over time, muscle weakening worsens
• If the heart muscles are affected, then arrhythmia and sudden cardiac problems can occur, which may even be fatal

Additional and Relevant Useful Information for Limb-Girdle Muscular Dystrophy Type 1B:

The following DoveMed website link is a useful resource for additional information:

http://www.dovemed.com/diseases-conditions/rare-disorders/