Nemaline myopathy. Evidence of dipeptidyl peptidase I deficiency

Fluorescent protease histochemical analysis of muscle biopsy specimens from two patients with nemaline myopathy revealed the apparent absence of one proteolytic enzyme, dipeptidyl peptidase. Although the function of peptidases in normal muscle is obscure, this abnormality suggests that proteases may participate in posttranslational modification of proteins that are to be assembled into Z lines or, alternatively, in the disassembly and degradation of Z-line material.     

Nemaline myopathy and cardiomyopathy.

A case report is presented in which a 4-year-old male is diagnosed with hypertrophic cardiomyopathy, respiratory distress, muscle hypotonia, and psychomotor retardation. Electron microscopic study of skeletal muscle biopsy revealed pathologic changes typical of congenital nemaline myopathy, and biochemical analysis revealed a disorder of mitochondrial fatty acid oxidation. Therefore a previously undescribed combination of a structural and metabolic myopathy is reported.     

Nemaline myopathy, an integrated study: selective extraction.

Low ionic strength extraction of glycerinated skeletal muscle containing nemaline rods removes Z lines before rods or M lines. Low ionic strength extraction also removes Z lines in nemaline muscle more rapidly than in control muscle. Partial extraction of nemaline rods uncovers a highly ordered filament lattice consisting of a set of longitudinal filaments and another set of filaments that pass obliquely to the longitudinal filaments. Spacing and intercepts of the filaments in this lattice are responsible for the longitudinal and transverse periodicities seen in the intact rod. The structure in the rod lattice between adjacent minor transverse periods appears similar to the structure of native Z lines and permits the interpretation that the nemaline rod is a lateral polymer of Z-line subunits. Polyacrylamide gel electrophoretic analysis of the low ionic strength extracts of nemaline muscle, done both in denaturing (SDS) and nondenaturing solvents, reveals that the extracts contain α-actinin and tropomyosin, but do not contain large quantities of new or unknown proteins. Nemaline rods may owe their resistance to low ionic strength extraction to their highly ordered, crystalline lattice, to their sequence of very stable longitudinal filaments, or to both these features. Large deposits of spherical, 200-Å particles in nemaline muscle were identified as glycogen.     

Nemaline myopathy of cats

An apparently inherited myopathy, characterized by the presence of large numbers of nemaline rods in skeletal muscle fibers, was investigated in five cats. Onset of signs varied from 6 months to 1.5 years of age and consisted of reluctance to move, jerky gait and muscle twitching, hyporeflexia, and muscle wasting, which was most prominent in the proximal muscles of the forelimbs. All of the cats, three males and two females, were from the same dam. In addition to the presence of rods, the myopathy was characterized by marked fiber size variation, with atrophy of type 1 and type 2a muscle fibers. In addition, there was infolding of the sarcolemma and fiber splitting. Ultrastructurally, the rods closely resembled those described in human nemaline myopathy.     

Nemaline myopathy appearing in adults as cardiomyopathy. A clinicopathologic study

We examined a 29-year-old woman with nemaline myopathy that appeared as cardiomyopathy. Clinical examination showed dilated cardiomyopathy, but no neuromuscular abnormalities of the skeletal muscles. Electromyography showed neither neurogenic nor myopathic abnormalities. A biopsy specimen from the quadripecs muscle showed typical nemaline bodies in about 50% of the muscle fibers. The patient died six months later of biventricular heart insufficiency. Autopsy revealed nemaline bodies in the working and conducting tissues of the myocardium. Earlier, the patient's mother and one of her sisters died unexplained, sudden deaths at the ages of 47 and 37 years, respectively. Sections of the myocardium taken from the sister at autopsy were available, and also disclosed nemaline bodies after restaining with trichrome.     

Nemaline myopathy: a clinical study of 143 cases

We report 143 Australian and North American cases of primary nemaline myopathy. As classified by the European Neuromuscular Centre guidelines, 23 patients had severe congenital, 29 intermediate congenital, 66 typical congenital, 19 childhood-onset, and 6 adult-onset nemaline myopathy. Inheritance was autosomal recessive in 29 patients, autosomal dominant in 41, sporadic in 72, and indeterminate in 1. Twenty-two patients had skeletal muscle actin mutations and 4 had mutations in the alpha-tropomyosin(slow) gene. Obstetric complications occurred in 49 cases. Seventy-five patients had significant respiratory disease during the first year of life, and 79 had feeding difficulties. Atypical features in a minority of cases included arthrogryposis, central nervous system involvement, and congenital fractures. Progressive distal weakness developed in a minority of patients. Thirty patients died, the majority during the first 12 months of life. All deaths were due to respiratory insufficiency, which was frequently underrecognized in older patients. Arthrogryposis, neonatal respiratory failure, and failure to achieve early motor milestones were associated with early mortality. Morbidity from respiratory tract infections and feeding difficulties frequently diminished with increasing age. Aggressive early management is warranted in most cases of congenital nemaline myopathy.     

Nemaline myopathy: two autopsy reports

Nemaline myopathy belongs to the group of congenital non-progressive myopathies; however, in rare cases death occurs in early infancy. We report two cases of rapidly fatal nemaline myopathy. The first patient, who died at the age of 26 months, showed atrophy of type 1 fibers containing numerous rods in biopsy sections. Biopsy of the second patient, who had died at the age of 5 months, revealed severe maturational arrest and myopathy, but rods were so rare that diagnosis could only be made at the ultrastructural level. Autopsy of both patients showed that atrophy of type 1 fibers and maturational arrest had disappeared in the very same muscles; rods had moved to a central position in the first and significantly increased in number in the second case. Diaphragma muscles contained abundant amounts of rods in both cases. The cardiac musculature showed a few rods only in the first patient, who had developed heart insufficiency 11 months prior to death. Immunohistochemical analysis showed that rods did not contain desmin or ubiquitin.     

Nemaline rod myopathy: a rare form of myopathy

Nemaline rod myopathy (NM) is a rare form of congenital myopathy characterized by slowly progressive or nonprogressive muscle weakness and pathognomonic rod-like structures within the muscle fibers. To the best of our knowledge, this is first documentation of the clinicopathological features of this rare entity from India. All cases of NM diagnosed in our laboratory were retrieved. Clinical and pathological features were reviewed. During a period of 1.5 years (Jan 2004 to June 2005), we received 750 muscle biopsies for various reasons. Of which, 15 were diagnosed as congenital myopathies and four as nemaline rod myopathies. Thus, NM comprises 0.53% of all muscle diseases and 22.6% of all congenital myopathies. All of them presented in childhood (first five years of life) with generalized hypotonia, feeding problems, repeated respiratory infections and muscle weakness. Both males and females were equally affected. The CPK levels were normal and EMG was myopathic. Microscopic examination revealed minimal changes but characteristic red-colored material was seen on modified Gomori trichrome staining which was immunopositive to alpha actinin. Ultrastructural examination confirmed this material to be nemaline rods. NM, although a rare form of congenital myopathies, should be suspected in children who present with generalized hypotonia, repeated chest infections and slowly progressive muscle weakness. This report highlights the importance of histochemistry and ultrastructural examination in the diagnosis of this entity, in the absence of the availability of methodology for genetic studies.     

Nemaline myopathy associated with hypertrophic cardiomyopathy

Nemaline myopathy is not usually considered to involve cardiac muscle and rarely is associated with nocturnal hypoventilation. We report a boy, 5 1/2 years of age, with nemaline myopathy who presented with respiratory failure. Echocardiography demonstrated the septum to left ventricular posterior wall ratio to be increased which is consistent with a hypertrophic cardiomyopathy. Because of nocturnal hypoventilation, tracheostomy was placed for ventilatory assistance. A process involving both muscle and nervous tissue may underlie this congenital myopathy; routine cardiac and pulmonary function evaluations may be indicated in these patients.     

Nemaline myopathy rod bodies: Structure and composition

Ca²⁺-activated protease (CAF) digestion of glycerinated nemaline myopathy muscle removed the electron-dense material covering rods and Z-lines and exposed longitudinal backbone filaments, 6–7 nm wide, which span the lengths of the original rods. Decoration of the exposed filaments (which are responsible for the periodicity parallel to the long axis of intact namaline rods) with heavy meromyosin (HMM) proved they are actin filaments. After CAF treatment, cross-striated periodical patterns in longitudinal sections and Z-filament-like proteins connecting actin filaments seen in cross-section disappeared. This suggests that α-actinin may be involved in formation of this pattern because of the specificity of CAF toward α-actinin. Gel electrophoresis of CAF-treated nemaline muscle showed that most α-actinin is released into the supernatant, whereas the residue is mainly actin and myosin. Electron microscope examination of longitudinal sections of intact rods shows an oblique filament pattern, thin (7 nm) lines, thick (11 nm) lines, and an amorphous appearance previously observed in normal Z-lines; patterns observed depend on sectioning angle and section thickness. In cross-section, rods show small square net (SS) and basket-weave (BW) forms. The SS form predominates, and coexistence of the 2 forms, which also occur in normal Z-lines, is observed.Results support the idea that rods are lateral polymers of Z-line units. We think that the length of rods, as well as the width of Z-lines, is determined by the amount of overlap of actin filaments of opposite polarity. Initiation of rod formation may be due to deregulation of actin filament length.     

Nemaline myopathy type 6: clinical and myopathological features

Nemaline myopathy (NEM) is one of the most common congenital myopathies. A unique subtype, NEM6, maps to chromosome 15q21-q23 in two pedigrees, but the causative gene has not been determined. We conducted clinical examination and myopathological studies in a new NEM family. Genotyping and gene screening were accomplished by searching known and 18 new candidate genes. The disease started in childhood by affecting proximal and distal muscles and causing slowness of movements. Muscle biopsies showed numerous nemaline rods and core-like formations. Suggestive linkage to chromosome 15q22-q23 was established. Genes known to be mutated in NEM or core-rod myopathy were screened and excluded. No pathogenic mutations were identified in other candidate genes. The disease in this Spanish family was classified as NEM6. It is phenotypically similar and probably allelic to the two previously reported NEM6 pedigrees. Further studies of these families will lead to the identification of the NEM6 gene.     

Nemaline myopathy caused by absence of alpha-skeletal muscle actin

OBJECTIVE: To investigate seven congenital myopathy patients from six families: one French Gypsy, one Spanish Gypsy, four British Pakistanis, and one British Indian. Three patients required mechanical ventilation from birth, five died before 22 months, one is ventilator-dependent, but one, at 30 months, is sitting with minimal support. All parents were unaffected. METHODS: The alpha-skeletal muscle actin gene (ACTA1) was sequenced. Available muscle biopsies were investigated by standard histological and electron microscopic techniques. The expression of various proteins was determined by immunohistochemistry, western blotting, or both. RESULTS: Three homozygous ACTA1 null mutations were identified: p.Arg41X in the French patient, p.Tyr364fsX in the Spanish patient, and p.Asp181fsX10 in all five British patients. An absence of alpha-skeletal muscle actin protein but presence of alpha-cardiac actin was shown in all muscle biopsies examined, with more alpha-cardiac actin in the biopsy from the child with the greatest muscle function. Muscle biopsies from all patients exhibited nemaline bodies whereas three also contained zebra bodies. INTERPRETATION: The seven patients have recessive nemaline myopathy caused by absence of alpha-skeletal muscle actin. The level of retention of alpha-cardiac actin, the skeletal muscle fetal actin isoform, may determine alpha-skeletal muscle actin disease severity. This has implications for possible future therapy.