Early predictors of poor outcome in congenital fiber-type disproportion myopathy

A fatal case of cor pulmonale with undetected chronic hypoventilation in an infant with a known congenital myopathy

The authors of this paper wish to present a case of fatal cor pulmonale with right ventricular hypertrophy complicated by a congenital myopathy. It is our intention to demonstrate the importance of vigilant clinical assessment of children with a congenital myopathy, regardless of the exact etiology of their disease, or family history of disease severity. This case highlights the risk for fatal complications if hypoventilation and respiratory insufficiency go unrecognized in myopathic children. Consequently, we recommend respiratory and cardiac monitoring surveillance as well as appropriate referral to specialists in the management of such children.

Congenital myopathies in Israeli families

The clinical features of 37 patients from 32 Israeli families with congenital myopathies evaluated between 1983 and 2004 are described: 13 children were diagnosed with congenital fiber type disproportion, 10 had myotubular myopathy, 7 had nemaline myopathy, 5 had central core disease, 1 had actin myopathy, and 1 had multi-minicore disease. There were 7 families (22%) that had parental consanguinity, and 4 families (12%) had more than 1 patient with congenital myopathy. Of the patients, 31 (84%) presented with clinical symptoms before 4 months of age, and 6 children (16%) presented after 1 year of age. Thirteen children (35%) had a severe phenotype with chronic ventilatory dependence or mortality before the age of 11 years. Facial weakness was associated with a severe phenotype. There was a high rate of a severe clinical phenotype in patients with myotubular myopathy (60%) and in patients with nemaline myopathy (57%), whereas in patients with congenital fiber type disproportion and in patients with central core disease, the proportion of a severe phenotype was lower (23% and 0%, respectively).

Autosomal dominant congenital fibre type disproportion: a clinicopathological and imaging study of a large family

Congenital fibre type disproportion (CFTD) is considered a non-progressive or slowly progressive muscle disease with relative smallness of type 1 fibres on pathological examination. Although generally benign, CFTD has a variable natural course and severe progression has been observed in some patients. The pathogenesis of the disorder is unknown and many authors consider CFTD a syndrome with multiple aetiologies rather than a separate clinical entity. A positive family history has been reported in about 40% of cases, but the inheritance pattern is not clear. Both autosomal recessive and dominant modes of inheritance have been suggested. The present paper describes a large, multigenerational kindred that has an inherited myopathy fulfilling the histological criteria of CFTD, with autosomal dominant transmission and high penetrance. The clinical picture, remarkably similar in all affected family members, started in early infancy with mild limb muscle weakness. There was slow progression of symptoms into adulthood, with moderate to severe, mainly proximal, muscle weakness without loss of ambulation. Muscle biopsy from two affected individuals demonstrated predominance of small type 1 muscle fibres without other significant findings. Nerve conduction studies were normal and needle electromyography showed a myopathic pattern. MRI examination performed on three patients from successive generations showed involvement of proximal limb and paraspinal muscles. The clinical and pathological homogeneity in the present family, together with the lack of additional histological abnormalities after decades of disease progression in two affected individuals, supports this being a distinct myopathy with fibre type disproportion. Whether the disease in this family can be regarded as a form of the congenital myopathy known as CFTD or rather a unique condition sharing histological features with CFTD needs further investigation. This is, to our knowledge, the largest kindred with muscle fibre type disproportion reported to date. Our data confirm autosomal dominant inheritance, and this is the first MRI document of this disorder.

Congenital Fiber Type Disproportion—30 Years On

Thirty years ago, M. H. Brooke coined the term "congenital fiber type disproportion" (CFTD) to describe 12 children who had clinical features of a congenital myopathy and relative type 1 fiber hypotrophy on muscle biopsy. It is now clear that this histological pattern can accompany a wide range of neurological disorders, leading to disillusionment with CFTD as a distinct nosological entity. To determine whether the CFTD has clinical utility as a diagnostic entity, we have reviewed the literature for cases of type 1 fiber hypotrophy and have used strict exclusion criteria to identify 67 cases of CFTD. Most patients presented at birth with weakness and hypotonia, had normal intelligence, and followed a static or improving clinical course. In 43% of families, more than 1 individual was affected. Failure to thrive was common and 25% of patients had contractures or spinal deformities. Bulbar weakness and ophthalmoplegia were less common and cardiac involvement was rare. Twenty-five percent followed a severe course and 10% had died at the time of reporting, all from respiratory failure. Ophthalmoplegia and facial and bulbar weakness were significantly associated with a poorer prognosis. The relatively homogeneous phenotype supports the retention of CFTD as a distinct diagnostic entity and familial occurrence suggests a genetic basis. Regarding the diagnosis of CFTD, we found no strong evidence that the minimum difference between type 1 and type 2 fiber sizes should be increased from 12% to 25%. We also list the other reported causes of relative type 1 fiber hypotrophy to aid their exclusion from CFTD.

Pulmonary hypoplasia in the myogenin null mouse embryo

Although fetal breathing movements are required for normal lung development, there is uncertainty concerning the specific effect of absent fetal breathing movements on pulmonary cell maturation. We set out to evaluate pulmonary development in a genetically defined mouse model, the myogenin null mouse, in which there is a lack of normal skeletal muscle fibers and thus skeletal muscle movements are absent in utero. Significant decreases were observed in lung:body weight ratio and lung total DNA at embryonic days (E)14, E17, and E20. Reverse transcriptase/polymerase chain reaction, in situ immunofluorescence, and electron microscopy revealed early lung cell differentiation in both null and wild-type lungs as early as E14. However at E14, myogenin null lungs had decreased 5'-bromo-2-deoxyuridine incorporation compared with that of wild-type littermates, whereas at E17 and E20, increased Bax immunolabeling and terminal deoxyribonucleotidyl transferase-mediated dUTP-biotin nick-end labeling staining were detected in the myogenin null mice but not in the wild-type littermates. These observations highlight the importance of skeletal muscle contractile activity in utero for normal lung organogenesis. Null mice lacking the muscle-specific transcription factor myogenin exhibit a secondary effect on lung development such that decreased lung cell proliferation and increased programmed cell death are associated with lung hypoplasia.

Congenital fiber type disproportion: severe form with marked improvement

A 30-month-old male exhibited marked hypotonia at birth accompanied by respiratory distress necessitating ventilator support. He subsequently demonstrated marked improvement in muscle power. He became independent of the respirator at 21 days of age and was able to sit without support at 11 months and walked alone at 24 months. Histopathologic analysis of the quadriceps femoris muscle confirmed the diagnosis of congenital fiber type of disproportion at 11 months of age. No other studies have described a patient with a severe neonatal form of congenital fiber type of disproportion who demonstrated such clear improvement. Physicians should be aware of this possibility when they interact with such patients and their families.

Human bHLH transcription factor gene myogenin (MYOG): genomic sequence and negative mutation analysis in patients with severe congenital myopathies

The myogenin gene encodes an evolutionarily conserved basic helix-loop-helix transcription (bHLH) factor that is required for differentiation of skeletal muscle, and its homozygous deletion in mice results in perinatal death from respiratory failure due to the lack of muscle fibers. Since the histology of skeletal muscle in myogenin null mice is reminiscent of that found in severe congenital myopathy patients, many of whom also die of respiratory complications, we sought to test the hypothesis that an aberrant human myogenin (myf4) coding region could be associated with some congenital myopathy conditions. With PCR amplification, we found similarly sized PCR products for the three exons of the myogenin gene in DNA from 37 patient and 40 control individuals. In contrast to previously reported sequencing of human myogenin (myf4), we describe with automated sequencing several base differences in flanking and coding regions plus an additional 659 and 498 bp in the first and second introns, respectively, in all 37 patient and 40 control samples. We also find a variable length (CA)-dinucleotide repeat in the second intron, which may have utility as a marker for future linkage studies. In summary, no causative mutations were detected in the myogenin coding locus of genomic DNA from 37 patients with severe congenital myopathy.

Cardiac manifestations of congenital fiber-type disproportion myopathy

Cardiac involvement has not been a reported feature of congenital fiber-type disproportion myopathy. We describe two children, aged 13 years and 1 year, respectively, who presented with serious cardiac symptomatology in conjunction with congenital fiber-type disproportion. One child developed dilated cardiomyopathy and medically intractable congestive heart failure necessitating cardiac transplantation at the age of 13 years. The second (unrelated) child developed atrial fibrillation with rapid atrioventricular conduction requiring treatment with digoxin. Skeletal muscle biopsy findings in both children showed congenital fiber-type disproportion with no evidence of a structural, dystrophic, or metabolic myopathy. Adenosine triphosphatase (ATPase) reacted sections showed type I hypotrophy with a predominance of type I fibers, confirmed by histogram analysis. Examination of the heart from patient 1 at the time of transplantation confirmed dilated cardiomyopathy with hypertrophic myocardiocytes. Although cardiomyopathy is commonly associated with other childhood myopathies, to our knowledge it has not been a feature in reported cases of congenital fiber-type disproportion. We recommend close cardiac assessment, with annual electrocardiograms, of children with congenital fiber-type disproportion.

Sequential muscle biopsy changes in a case of congenital myopathy

Muscle biopsies at age 7 months in a set of dizygotic male twins born floppy showed typical features of congenital fiber-type disproportion (CFTD). One of the twins died at age 1 year due to respiratory complications. The second one subsequently developed facial diplegia and external ophthalmoplegia. He never walked, remained wheelchair bound, and required continuous ventilatory support. He underwent repeat biopsies at ages 2 and 4, which showed many atrophic type 1 muscle fibers containing central nuclei and severe type 2 fiber deficiency compatible with centronuclear myopathy (CNM). Two-dimensional gel electrophoresis of muscle showed decreases of type II myosin light chains 2 and 3, suggestive of histochemical type I fiber deficiency. The progressive nature of morphological changes in one of our patients cannot be explained by maturational arrest. Repeat biopsies in cases of CFTD with rapid clinical deterioration may very well show CNM.

A follow-up study of congenital non-progressive myopathies

To determine the development and prognosis of patients with the moderate congenital form of congenital non-progressive myopathies (CNM), we investigated 55 patients with CNM by questionnaires. This patient group included 18 with nemaline myopathy, 11 with central core disease, 3 with myotubular myopathy, 15 with congenital fiber type disproportion and 3 with minicore disease. As to motor development, almost all patients had learned to walk alone by 3 years of age, averaging 2 2/12 years. Central nervous system involvement including mental retardation was seen in 24% of the patients, predominantly in patients with myopathy. The level of mental retardation was not related to the severity of muscle weakness. Patients with central core disease had a higher frequency of skeletal deformities. CNM were not necessarily benign in their prognosis as previously thought, but sometimes showed progressive deterioration leading to death. In 16% of patients, progressive deterioration in muscle strength and respiratory function became manifest after once the patient became ambulant. Even in the benign congenital form, seven of 55 patients died from respiratory or cardiac failures by 20 years of age. Therefore evaluation of cardiopulmonary function at regular intervals is important in the continuing care of patients with CNM.

Congenital myopathies

Several dozen congenital myopathies are defined by clinical and morphological criteria. The application of the current generation of scientific techniques including immunohistochemistry and molecular genetics has resulted in the expansion of our knowledge and understanding of the well-established conditions including central core myopathy and centronuclear/myotubular myopathy and allowed greater understanding of the interrelationships of some of the less common or less well-established conditions. In the near future molecular genetics may allow the identification of the specific gene defect in many of these diseases. This article reviews the major congenital myopathies and presents some of the information gained by application of new technology to these conditions.