Clinical, Pathological And Molecular Biological Study On Autosomal Dominant Inherited Centronuclear Myopathy

Objective:The centronuclear myopathies(CNMs)are a group of pathologically defined disorders that characteristically have a high proportion of small myofibers with centrally placed nuclei.Spiro and colleagues first coined the term"myotubular myopathy" in 1966,They described a myopathy in a 12-year-old boy who had generalized muscle weakness since birth,ophthalmoplegia,and ptosis.Muscle biopsy was characterized by numerous small myofibers with centrally placed nuclei that were surrounded by a clear zone on hematoxylin and eosin(H&E)-stained sections. Currently,the term myotubular myopathy is restricted to the severe neonatal X-linked form(X-MTM),which is caused by MTM1 gene mutations,while the term centronuclear myopathy was preferred for the autosomal forms of the disorder. Recently,different missense mutations affecting the middle domain of the dynamin 2 (DNM2,19p13.2)were shown to cause autosomal dominant CNM.DNM2 encodes a protein involved in endocytosis and membrane trafficking,actin assembly and centrosome cohesion.The DNM2 protein comprises an N-terminal tripartite GTPase domain,a middle domain,a Pleckstrin Homology(PH)domain,a GTPase effector domain(GED)and a C-terminal proline rich domain(PRD).Interestingly,DNM2 mutations,restricted to the PH domain,were identified in dominant Charcot-Marie-Tooth disease type B(DNM2-CMT2B).In 2008 Zhang Yongqing was first described a family of AD CNM with the mutation of DNM2 in China.The aim of the present study is to describe another family of of AD CNM with the mutation of DNM2.And define the clinical,pathology and the mutation characteristics of this family. Material and methods:The four cases are from the department of neurology of Qilu hospital, Shandong university.Two of they were diagnosed through clinical manifestation and pathology of muscle biopsy.Genomic DNA was extracted from peripheral blood of the affected family that were followed up,with phenol/chloroform procedure.Exon 8 of DNM2 gene were amplified by polymerase chain reaction(PCR).DNA fragment was analyzed by the agrose gel electrophoresis.We sequenced the exon 8 and their flanks for detecting gene mutation.And then analyzed with summarized clinical and pathological features of the DNM2 CNMs.Result:1.The family includes 4 patients,2 males and 2 females.The initial symptom of the 4 patients is weakness of lower extremities.But wheather the weakness is pronounced in distal(hand and finger extensor)or in proximal muscles is not consistence in this 4 patients.Four individuals displayed mild facial weakness. And one of them has extraocular involvement.Muscular atrophy is also prominent. Serum creatine kinase is normal in proband.The EMG of two patients showed myopathy change.2.The most prominent histopathological features include high frequency of centrally located nuclei in a large number of the extrafusal muscle fibers,radial arrangement of sarcoplasmic strands around the central nuclei and predominant and hypotrophy of type I fiber.Marked intrafascicular adipose infiltration is seen in both two patients.3.Exon 8 of DNM2 were analyzed by PCR and sequencing,1106G→A mutation was revealed in 7 members of this family.Conclusions1.This pedigree was verified as CNM by clinical,pathological and genetic researches.And as the same as Europe characterized by slowly progressive generalized muscular weakness and atrophy usually beginning in childhood or early adolescence.Ptosis and involvement of the extraocular eye muscles are frequent findings.Morphologically characterized by chains of centrally located nuclei in a large number of(extrafusal)muscle fibres,a predominance and hypotrophy of type I fibres and a radial arrangement of sarcoplasmic strands around the centralnuclei seen on nicotinamide adenosine dinucleotide-tetrazolium reductase staining(NADH-TR)and on immunostaining of desmin.The mechanism of marked intrafascicular adipose infiltration in both two patients isunknown by now.2.7 members of this family carriy the mutation of 1106 G→A.DNM2 gene mutation is confirmed again in Asian autosomal dominant inherited CNM pedigree.AlthoughⅢ2(4 years old),Ⅲ3(4 years old)andⅢ4(5 years old) carry the mutation of DNM2,they are too young to manifest the syndrome of weakness.