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Juvenile-onset Steinert myotonic dystrophy(Juvenile-onset Steinert myotonic dystrophy)

来源:百科 / 时间: 2024-11-24

Juvenile-onset Steinert myotonic dystrophy (JSMD), also known as Juvenile-onset myotonic dystrophy type 1 (DM1), is a rare and severe form of myotonic dystrophy that typically presents in childhood or adolescence. It is characterized by early-onset muscle weakness, myotonia (delayed muscle relaxation), and multisystem involvement.

疾病机制

Juvenile-onset Steinert myotonic dystrophy (JSMD) is caused by an expansion of a trinucleotide (CTG) repeat in the DMPK gene on chromosome 19. The number of repeats typically ranges from 100 to 1,000, which is significantly higher than the normal range of 5-37 repeats. This expansion leads to the production of toxic RNA and proteins, resulting in a toxic gain-of-function mechanism that disrupts normal cellular processes, particularly in muscle and brain tissues.

临床表现

  • Muscle Weakness and Myotonia: Early-onset muscle weakness, often starting in the lower limbs, and myotonia, which is the inability of muscles to relax after contraction.
  • Cardiac Involvement: Arrhythmias, such as atrial fibrillation, and conduction abnormalities.
  • Cognitive and Behavioral Issues: Intellectual disability, learning difficulties, and behavioral problems.
  • Endocrine Dysfunction: Insulin resistance, diabetes mellitus, and hypogonadism.
  • Respiratory Issues: Respiratory muscle weakness leading to sleep apnea and respiratory insufficiency.
  • Other Features: Cataracts, frontal balding, and gastrointestinal dysmotility.

诊断

  • Clinical Evaluation: Detailed history and physical examination, focusing on muscle weakness, myotonia, and multisystem involvement.
  • Genetic Testing: Confirmation of the disease through molecular genetic testing, which detects the expanded CTG repeat in the DMPK gene.
  • Electrocardiogram (ECG): To assess cardiac involvement.
  • Muscle Biopsy: Rarely performed but can show characteristic findings such as nuclear cataracts and muscle fiber atrophy.

遗传咨询

  • Autosomal Dominant Inheritance: JSMD follows an autosomal dominant pattern of inheritance, meaning that one copy of the mutated gene in each cell is sufficient to cause the disorder.
  • Penetrance and Expressivity: High penetrance but variable expressivity, meaning that not all individuals with the mutation will show the same severity of symptoms.
  • Prenatal and Preimplantation Diagnosis: Available for families at risk, allowing for the identification of the mutation in the fetus or embryos.
  • Counseling on Family Planning: Discussing the risks and options for family planning, including the use of assisted reproductive technologies.

预后

The prognosis for individuals with Juvenile-onset Steinert myotonic dystrophy is generally poor, with a significant impact on quality of life and lifespan. Early-onset symptoms and multisystem involvement contribute to a more severe course of the disease compared to adult-onset forms. Management focuses on supportive care, addressing specific symptoms, and optimizing quality of life. Regular monitoring and multidisciplinary care are essential to manage the various complications associated with the disease.

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