Pseudohypertrophic muscular dystrophy, also known as Duchenne-type muscular dystrophy (DMD) ( OMIM 310200 ). It is the most common type of progressive myotonic dystrophy. The prevalence is 3.3/100,000, accounting for 20-30/100,000 male births, and is an X-linked recessive trait. It is predominantly in boys, with females being the carriers of the causative gene. The onset is usually around 5 years of age. Myasthenia gravis is progressive, which is characteristic of the disease, and the prognosis is poor. The disease is caused by mutations in the DMD gene encoding dystrophin, and about 1/3 of cases are disseminated, without a family history, and are caused by de novo mutations in the gene. Becker muscular dystrophy is also caused by mutations in the DMD gene, but usually the abnormal DMD protein produced after the mutation still has some function, so the clinical symptoms are much less severe than those of DMD. Clinical manifestations】 The activities of the child at birth, such as head lifting and sitting, are normal, but after the age of 1 year, the child starts to have difficulty in standing and walking. The child is clumsy, falls easily, walks wobbly, and has difficulty ascending stairs or rising from a sitting or lying position. As the lesion progresses, the weakness of the gluteus medius muscle leads to a special duck stance when walking. The child needs to turn over to prone when rising from the supine position, and then stand slowly with both hands supporting the ground and lower limbs, which is called Gower’s sign. The child’s gastrocnemius muscle gradually becomes pseudohypertrophied and the tendon reflex is weakened or disappears. Some patients exhibit abnormal behavior. Most children eventually become bedridden and die before the age of 20 years due to spasticity, decubitus ulcers and pneumonia. Patients with BMD generally have mild clinical symptoms and can survive into adulthood. About 1/4 of children with BMD have mental retardation, significantly elevated blood phosphocreatine kinase (CRK) concentrations up to 10,000 times the normal value, and electromyography showing myopathic changes with mild loss of innervation potential; muscle biopsy shows both muscle fiber necrosis and regeneration with connective tissue hyperplasia. Diagnosis and prevention】 Based on the patient’s specific symptoms and signs, combined with blood CPK enzymatic examination and electromyography, it is generally not difficult to make a diagnosis. The diagnosis can be confirmed by multiplex PCR technique, Southern hybridization, and point mutation examination. For families with unspecified mutations, STR loci can be used for linkage analysis for carrier detection or prenatal diagnosis. The only effective way to prevent DMD is prenatal diagnosis of high-risk fetuses and abortion after diagnosis. Genetic counseling] The disease is an X-linked recessive disorder. One third of cases of fatal sporadic X-linked recessive inheritance are caused by de novo mutations (also known as Haldane’s law), which should be especially noted during family analysis. Frequently asked questions: 1. Is it possible to have DMD even if no similar cases are found in the family? As mentioned earlier, about 1/3 of DMD cases are caused by de novo mutations, i.e., both parents have normal DMD genes, but when the individual embryo develops, a mutation in the DMD gene occurs, resulting in the development of the disease. This mutation occurs in individuals that can pass on the disease-causing gene to their offspring. 2.How to avoid the genetic risk of DMD through sex selection? The disease mainly develops in males, and the risk of DMD can be reduced through prenatal diagnosis in families who have already given birth to patients with DMD. If genetic diagnosis can be applied to exclude the mutation of DMD gene in the male fetus conceived, it is still possible to have a normal male fetus.