Benign pseudohypertrophic muscular dystrophy

Introduction Becker type progressive muscular dystrophy progresses slowly (the course can reach more than 25 years, often can still walk after 20 years old); more often without myocardial involvement or only mild involvement, the prognosis is good, also known as benign type.

Cause

(1) Causes of the disease

The disease is a hereditary disease, multi-attribute linkage recessive inheritance, and individual staining recessive inheritance.

(two) pathogenesis

The molecular biology method has been used to locate the DMD gene on X chromosome Xp21.1~Xp21.3, and the disease-causing gene is dystrophin gene. It is the largest human gene discovered so far, about 2000kb or more, containing 79 exon coding. , a 14 kb transcribed region. Studies have shown that 60% to 70% of DMD is due to gene deletion or repeated mutations.

Gene deletions were non-randomly distributed, mainly in the central region of the gene (80%), with a few occurring at the 5th (20%). Large gene deletions often start at the 5th end of the gene, and gene deletions cause the destruction of open reading frames, leading to DMD performance. In patients with BMD, the missing gene maintains a translational reading frame and produces a protein with half the function and shortened length. The "reading frame" hypothesis explains the different clinical types of 92% of patients with DMD/BMD.

Dystrophin is part of the dystrophin glycoprotein complex (DGC), a complex of membrane-associated proteins that spans the sarcolemmal membrane and connects the cytoskeleton and extracellular matrix within the cell. In duchenne muscular dystrophy patients, the loss of DGC components due to the loss of dystrophin can be normally synthesized but not properly assembled and integrated into the muscle fiber membrane. It is speculated that due to the damage of DGC, a series of chain reactions are triggered, leading to the necrosis of muscle cells of DMD. The lack of dystrophin disrupts the association between the cytoskeleton and the extracellular matrix of the muscle fiber membrane, causing instability of the muscle fiber membrane, tearing of the membrane, and necrosis of muscle cells.

an examination

Related inspection

Hematopoietic cells in the blood around the electromyogram

Often started after the age of 10, the first symptom is weak pelvic and femoral muscles, slow progress, long course of disease, 25 years or more 25 years after the symptoms can not walk, most do not occur at 30-40 years old The prognosis is good.

Serum biochemical examination

Creatine phosphokinase (CK) is significantly elevated, reaching 15,000 to 20,000 U/L, or even higher. Elevated serum CK can occur at birth and is slightly reduced at the end of the disease.

2. Muscle biopsy

Characteristic pathological changes include scattered degenerative changes and necrotic muscle fibers. Over time, there is an increase in endometrial connective tissue and loss of muscle fibers, and replacement of adipose tissue.

3. Genetic diagnosis

The DMD gene is located at Xp21.1-21.3, and the protein encoded by the gene is dystrophin. After the 1990s, the major hospitals in China used nuclear-enhanced Southern blotting and polymerase chain reaction (PCR) analysis of missing hotspot exons for genetic diagnosis. The detection rate of deletion was 56.7%-63.0%, and the DMD gene deletion was used. The hot spot 9 pairs of primers PCR analysis, the detection rate of the missing large cases was 47.5% ~ 49.6%. Quantitative PCR assays and short tandem repeat linkage analysis have been used in China to detect DMD gene carriers. There is still no systematic study on the diagnosis of point mutation DMD.

4. Electromyogram

For myogenic changes, the diseased muscles are low, the waveform duration is shortened, and the multiphase waves are increased. Others should be checked for ECG, EEG, etc.

Differential diagnosis

Duchenne type malnutrition (DMD): also known as severe pseudo-fat large-scale malnutrition, almost only seen in boys, if the mother is a gene carrier, 50% of male offspring, usually starting from 2-8 years old, initial sense Walking benzoquinone, easy to fall, can not run and board the building, standing scalp, abdomen out, two feet open, walking slowly swinging, showing a special "duck step" gait, when walking from the back is very difficult, must first Turn over and prone, then climb your knees with both hands and gradually support the standing up (Gower sign). Can also be seen in the proximal muscles of the limbs, quadriceps and arm muscles.

Often started after the age of 10, the first symptom is weak pelvic and femoral muscles, slow progress, long course of disease, 25 years or more 25 years after the symptoms can not walk, most do not occur at 30-40 years old The prognosis is good.

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