A follow-up study of congenital non-progressive myopathies

Use of the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP INTEND) in X-Linked Myotubular Myopathy: Content Validity and Psychometric Performance

X-linked myotubular myopathy (XLMTM) is a life-threatening, congenital myopathy characterized by extreme hypotonia, weakness, delayed motor milestones, and respiratory failure, often resulting in pediatric mortality. This study evaluated the content validity and psychometric performance of the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders as a measure of neuromuscular functioning in children with X-linked myotubular myopathy. This study was conducted in two phases. Phase I assessed the content validity of the measure for use in an XLMTM pediatric population through: literature review, clinical expert interviews, caregiver interviews, and a modified-Delphi panel among clinicians. Phase II assessed psychometric performance based on the INCEPTUS observational clinical study and the ASPIRO interventional gene therapy study, including tests of reliability (internal consistency, test-retest, and interrater), validity (construct and criterion), and responsiveness based on observational and interventional clinical trial data analyses. Data established construct validity and reliability of the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders among XLMTM patients before administration of resamirigene bilparvovec, and sensitivity to study drug administration as evidenced by the significant post-administration response in ASPIRO. Findings support the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders as an appropriate neuromuscular functioning assessment in a pediatric X-linked myotubular myopathy patient population.

Congenital myopathies: Natural history of a large pediatric cohort

OBJECTIVE

To assess the natural history of congenital myopathies (CMs) due to different genotypes.

METHODS

Retrospective cross-sectional study based on case-note review of 125 patients affected by CM, followed at a single pediatric neuromuscular center, between 1984 and 2012.

RESULTS

Genetic characterization was achieved in 99 of 125 cases (79.2%), with RYR1 most frequently implicated (44/125). Neonatal/infantile onset was observed in 76%. At birth, 30.4% required respiratory support, and 25.2% nasogastric feeding. Twelve percent died, mainly within the first year, associated with mutations in ACTA1, MTM1, or KLHL40. All RYR1-mutated cases survived and did not require long-term ventilator support including those with severe neonatal onset; however, recessive cases were more likely to require gastrostomy insertion (p = 0.0028) compared with dominant cases. Independent ambulation was achieved in 74.1% of all patients; 62.9% were late walkers. Among ambulant patients, 9% eventually became wheelchair-dependent. Scoliosis of variable severity was reported in 40%, with 1/3 of (both ambulant and nonambulant) patients requiring surgery. Bulbar involvement was present in 46.4% and required gastrostomy placement in 28.8% (at a mean age of 2.7 years). Respiratory impairment of variable severity was a feature in 64.1%; approximately half of these patients required nocturnal noninvasive ventilation due to respiratory failure (at a mean age of 8.5 years).

CONCLUSIONS

We describe the long-term outcome of a large cohort of patients with CMs. While overall course is stable, we demonstrate a wide clinical spectrum with motor deterioration in a subset of cases. Severity in the neonatal/infantile period is critical for survival, with clear genotype-phenotype correlations that may inform future counseling.

Nemaline myopathy in a newborn infant: a rare muscle disorder

Nemaline myopathy (NM) is a genetically and clinically heterogeneous muscle disorder, defined by the presence of characteristic nemaline bodies on muscle biopsy. The disease has a wide spectrum of phenotypes, ranging from forms with neonatal onset and fatal outcome to asymptomatic forms. The neonatal form is severe and usually fatal. The clinical variability, with differing age of onset and severity of symptoms makes the diagnosis difficult during infancy. There is no curative treatment. L-tyrosine may prevent aspiration by reducing pharyngeal secretions and drooling. Most of the patients die from respiratory and cardiac failure. This article discusses a newborn infant who presented with generalized weakness and respiratory failure. Partial response to L-tyrosine treatment was noted. The case is worth presenting to remind clinicians of congenital myopathies in the differential diagnosis of floppy infant during neonatal period and to emphasize the importance of muscle biopsy in diagnosis.

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 myopathy caused by a novel missense mutation in the CFL2 gene

Nemaline myopathy and myofibrillar myopathy are heterogeneous myopathies that both comprise early-onset forms. We present two sisters from a consanguineous Iraqi Kurdish family with predominant axial and limb girdle weakness. Muscle biopsies showed features of both nemaline myopathy and myofibrillar myopathy. We performed homozygosity mapping in both siblings using an Affymetrix 250K Nspl SNP array. One of the overlapping homozygous regions harbored the gene CFL2. Because a mutation in CFL2 was identified in a family with nemaline myopathy, we performed sequence analysis of the gene and a novel homozygous missense mutation in exon 2 (c.19G>A, p.Val7Met) of CFL2 was identified in both siblings. CFL2 encodes the protein cofilin-2, which plays an important role in regulation of sarcomeric actin filaments. To our knowledge, this is the second family in which a mutation in CFL2 causes an autosomal recessive form of congenital myopathy with features of both nemaline and myofibrillar myopathy. Given the clinical variability and the multitude of histological features of congenital myopathies, CFL2 sequence analysis should be considered in patients presenting with an autosomal recessive form of congenital myopathy.

Consensus statement on standard of care for congenital myopathies

Recent progress in scientific research has facilitated accurate genetic and neuropathological diagnosis of congenital myopathies. However, given their relatively low incidence, congenital myopathies remain unfamiliar to the majority of care providers, and the levels of patient care are extremely variable. This consensus statement aims to provide care guidelines for congenital myopathies. The International Standard of Care Committee for Congenital Myopathies worked through frequent e-mail correspondences, periodic conference calls, 2 rounds of online surveys, and a 3-day workshop to achieve a consensus for diagnostic and clinical care recommendations. The committee includes 59 members from 10 medical disciplines. They are organized into 5 working groups: genetics/diagnosis, neurology, pulmonology, gastroenterology/nutrition/speech/oral care, and orthopedics/rehabilitation. In each care area the authors summarize the committee's recommendations for symptom assessments and therapeutic interventions. It is the committee's goal that through these recommendations, patients with congenital myopathies will receive optimal care and improve their disease outcome.

Congenital myopathies--a comprehensive update of recent advancements

The congenital myopathies are relatively newly discovered compared with other categories of muscle diseases. Current research continues to clarify and classify the congenital myopathies. These pose a diagnostic problem and cannot be diagnosed by routine hematoxylin and eosin stain. A lot of special techniques are required to diagnose them correctly and it's various subtypes. The disease specific structural changes seen in the muscle are detected by enzyme histochemistry, immunohistochemistry and electron microscopy. Through this review we provide an up-to-date analysis of congenital myopathies including clinical and pathologic aspects.

Centronuclear (myotubular) myopathy

Centronuclear myopathy (CNM) is an inherited neuromuscular disorder characterised by clinical features of a congenital myopathy and centrally placed nuclei on muscle biopsy.

The incidence of X-linked myotubular myopathy is estimated at 2/100000 male births but epidemiological data for other forms are not currently available.

The clinical picture is highly variable. The X-linked form usually gives rise to a severe phenotype in males presenting at birth with marked weakness and hypotonia, external ophthalmoplegia and respiratory failure. Signs of antenatal onset comprise reduced foetal movements, polyhydramnios and thinning of the ribs on chest radiographs; birth asphyxia may be the present. Affected infants are often macrosomic, with length above the 90^th centile and large head circumference. Testes are frequently undescended. Both autosomal-recessive (AR) and autosomal-dominant (AD) forms differ from the X-linked form regarding age at onset, severity, clinical characteristics and prognosis. In general, AD forms have a later onset and milder course than the X-linked form, and the AR form is intermediate in both respects.

Mutations in the myotubularin (MTM1) gene on chromosome Xq28 have been identified in the majority of patients with the X-linked recessive form, whilst AD and AR forms have been associated with mutations in the dynamin 2 (DNM2) gene on chromosome 19p13.2 and the amphiphysin 2 (BIN1) gene on chromosome 2q14, respectively. Single cases with features of CNM have been associated with mutations in the skeletal muscle ryanodine receptor (RYR1) and the hJUMPY (MTMR14) genes.

Diagnosis is based on typical histopathological findings on muscle biopsy in combination with suggestive clinical features; muscle magnetic resonance imaging may complement clinical assessment and inform genetic testing in cases with equivocal features. Genetic counselling should be offered to all patients and families in whom a diagnosis of CNM has been made.

The main differential diagnoses include congenital myotonic dystrophy and other conditions with severe neonatal hypotonia.

Management of CNM is mainly supportive, based on a multidisciplinary approach. Whereas the X-linked form due to MTM1 mutations is often fatal in infancy, dominant forms due to DNM2 mutations and some cases of the recessive BIN1-related form appear to be associated with an overall more favourable prognosis.

Central core disease due to recessive mutations inRYR1 gene: Is it more common than described?

Central core disease (CCD) is an autosomal-dominant congenital myopathy, with muscle weakness and malignant hyperthermia (MH) susceptibility. We identified two of nine Brazilian CCD families carrying two mutations in the RYR1 gene. The heterozygous parents were clinically asymptomatic, and patients were mildly affected, differing from the few autosomal-recessive cases described previously. Recessive inheritance in CCD may therefore be more common than previously appreciated, which has important implications for genetic counseling and MH prevention in affected families.

A benign congenital myopathy in an inbred Samaritan family

We describe a novel form of myopathy in a mother and her two daughters from an inbred Samaritan family. The patients displayed severe neonatal hypotonia, lethargy and dysmorphic features. Motor milestones were delayed; however, the hypotonia and muscle weakness gradually improved during the first 2 years of life and independent walking was achieved by 18 months. The mother at the age of 23 years shows myopathic facies and minimal proximal weakness. Her intelligence is normal. Her muscle biopsy revealed central nuclei and disruption of the intermyofibrillary network with moth eaten and spiral fibers. Mutations in SMN, MTM1 and the myotonic dystrophy genes were excluded. We suggest this is a new benign form of congenital myopathy. Inheritance is probably autosomal recessive.

Congenital myopathies

Most congenital myopathies have been defined on account of the morphological findings in enzyme histochemical preparations. In effect, the diagnosis of this group of diseases continues to be made on the histological pattern of muscle biopsies. However, progress has been made in elucidating the molecular genetic background of several of the congenital myopathies. In this updated review we address those congenital myopathies for which gene defects and mutant proteins have been found (central core disease, nemaline myopathies, desminopathy, actinopathy, certain vacuolar myopathies, and myotubular myopathy) and the other disease with central nuclei (centronuclear myopathy).

Floppy infant syndrome

Floppiness/hypotonia is a common neurologic symptom in infancy. A variety of neuromuscular disorders and central nervous system (CNS) disorders cause floppy infant syndrome (FIS). CNS disorders are the much more common causes of the syndrome than neuromuscular disorders. On long-term follow up, cerebral palsy and mental retardation turn out to be the 2 most common causes of FIS. This review focuses on neuromuscular causes of FIS. With the advent of molecular diagnosis, a few conditions can be diagnosed by DNA analysis of the peripheral lymphocytes (myotonic dystrophy, spinal muscular atrophy); however, for the most part, electrodiagnostic studies and muscle biopsy remain as essential diagnostic tools for FIS. Immunohistochemical study of the biopsied muscle also improves diagnostic capability. Management for most conditions remains supportive.

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.

Rod distribution and muscle fiber type modification in the progression of nemaline myopathy

Nemaline myopathy is a structural congenital myopathy associated with the presence of rodlike structures inside the muscle fibers and type I predominance. It may be caused by mutations in at least five genes: slow alpha-tropomyosin 3 (chromosome 1q22-23), nebulin (chromosome 2q21.1-q22), actin (chromosome 1q42), tropomyosin 2 (chromosome 9p13), and troponin T1 (chromosome 19q13.4). The effect of these mutations in the expression of the protein and the mechanism of rod formation is still under investigation. We analyzed the possibility of progressive alterations with time and/or disease evolution, such as transformation of type I to type II fiber and rod pattern and distribution in muscle fibers from patients with nemaline myopathy, through a morphometric and immunohistochemical analysis of different muscle protein isoforms. A tendency of diffuse rods to be organized in the subsarcolemmal region was observed in two patients who were submitted to subsequent biopsies after 10 and 13 years. Additionally, we observed the expression of type II protein isoforms in type I fibers and a higher proportion of type II fibers in the younger patient of a pair of affected sibs, giving further support to the hypothesis of progressive conversion of type II to type I fibers in nemaline myopathy.

Congenital and metabolic myopathies of childhood or adult onset

OBJECTIVES

To investigate the clinical presentation, histological findings, and outcome of patients with congenital and metabolic myopathies (CM and MM) in whom the disease was diagnosed in childhood or adulthood.

PATIENTS AND METHODS

We reviewed the diagnosis of all skeletal muscle biopsies performed by our group between 1984 and 1996 (13 years). All patients with CM and MM of childhood or adult onset were included in the study. Patients with mitochondrial myopathies were excluded because they are multisystemic disorders with a more distinct picture than that observed in other MM. We retrospectively reviewed the clinical history, with special emphasis on the clinical patterns of presentation, histological findings, and outcome.

RESULTS

Among 1,865 biopsies, 28 (1.5%) fulfilled the diagnostic criteria for CM (seven nemaline myopathies, four multicore myopathies, three centronuclear myopathies) or MM (five adult-onset acid maltase deficiency, three myophosphorylase deficiency, three phosphofructokinase deficiency, two carnitine palmitoyl transferase deficiency, and one carnitine deficiency). In nearly half of the patients, mild stable weakness was the major complaint, whereas in one third muscular symptoms were intermittent and related to exercise. In a small number of cases, a persistently raised serum creatine kinase in an asymptomatic patient was the reason for muscle biopsy. Histological examination of skeletal muscle was highly indicative of a specific muscle disease in 26 of the 28 cases. After a mean follow-up of 7 years, the outcome has generally been good, and in most patients the myopathy did not worsen, most remaining ambulatory.

CONCLUSION

CM and MM presenting in childhood or adulthood are infrequent; the symptoms are usually mild or moderate, and the prognosis generally is good.

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.