Mental retardation in congenital nonprogressive myopathy with uniform type 1 fibers

Interactions among ryanodine receptor isotypes contribute to muscle fiber type development and function

Mutations affecting ryanodine receptor (RyR) calcium release channels commonly underlie congenital myopathies. Although these channels are known principally for their essential roles in muscle contractility, mutations in the human RYR1 gene result in a broad spectrum of phenotypes, including muscle weakness, altered proportions of fiber types, anomalous muscle fibers with cores or centrally placed nuclei, and dysmorphic craniofacial features. Currently, it is unknown which phenotypes directly reflect requirements for RyRs and which result secondarily to aberrant muscle function. To identify biological processes requiring RyR function, skeletal muscle development was analyzed in zebrafish embryos harboring protein-null mutations. RyR channels contribute to both muscle fiber development and function. Loss of some RyRs had modest effects, altering muscle fiber-type specification in the embryo without compromising viability. In addition, each RyR-encoding gene contributed to normal swimming behavior and muscle function. The RyR channels do not function in a simple additive manner. For example, although isoform RyR1a is sufficient for muscle contraction in the absence of RyR1b, RyR1a normally attenuates the activity of the co-expressed RyR1b channel in slow muscle. RyR3 also acts to modify the functions of other RyR channels. Furthermore, diminished RyR-dependent contractility affects both muscle fiber maturation and craniofacial development. These findings help to explain some of the heterogeneity of phenotypes that accompany RyR1 mutations in humans.

Ophthalmoplegia in congenital neuromuscular disease with uniform type 1 fiber

Congenital neuromuscular disease with uniform type 1 fiber (CNMDU1) is a rare type of congenital myopathy. It is characterized by early onset of symptoms, mild proximal muscle weakness, hyporeflexia or areflexia, normal serum creatine kinase (CK) levels and myopathic electromyography finding, uniform type 1 fibers, and nonprogression. We report a 2-year-old boy who presented with congenital hypotonia, breathing and feeding difficulty, myopathic facies, proximal muscle weakness, ptosis, total external ophthalmoplegia and delayed motor developmental milestones. Normal serum muscle enzyme and short duration of motor unit potentials on electromyography were noted. Muscle biopsy showed uniformity of type 1 fibers (greater than 99%) and moderate variation in fiber size without specific structural abnormality. Total external ophthalmoplegia may be one of the important clinical manifestations of CNMDU1. It is important to recognize this disorder because it is nonprogressive in nature.

Kyphoscoliosis associated with congenital neuromuscular disease with uniform type 1 fibers

OBJECTIVE

To report the first case of surgical treatment for severe kyphoscoliosis associated with respiratory disorder in a patient with congenital neuromuscular disease with uniform type 1 fibers (CNMDU1), including management of the possible onset of malignant hyperthermia (MH) in general anesthesia. CNMDU1 is rare among congenital neuromuscular diseases, and surgery for spinal deformity in CNMDU1 has not been described. Onset of MH in general anesthesia is a concern in this disease.

METHODS

A 13-year-old female with motor retardation, suspected myopathy, and severe spinal deformity was followed at another pediatric hospital before referral to Meijo Hospital. Symptoms at the initial consultation were mild general muscular weakness and muscular atrophy. The rib hump was 60° and trunk balance was poor. The tendon reflex showed hyporeflexia, and blood tests were normal. Vital capacity was 0.69 L and forced expiratory volume percentage in 1 s was 75.5%, showing a restrictive and obstructive ventilatory defect. A plain radiograph showed severe kyphoscoliosis with thoracic scoliosis of 130° (T5-L1) and thoracic kyphosis of 110° (T2-T12) with almost no flexibility in bending or traction film.

RESULTS

After preoperative halo traction for 2 months, one-stage anterior and posterior correction and fusion from T2 to L3 was conducted. MH did not occur, but recovery of respiratory function required 8 days by intubation after surgery. Postoperatively, thoracic kyphosis improved to 25° and thoracic scoliosis was 66° (correction rate: 49%). Pathological results of an intraoperative muscle biopsy from the paraspinal muscles confirmed the diagnosis of CNMDU1. At 6 years after surgery, the patient has no problems in daily life and no respiratory difficulty.

CONCLUSION

Spinal deformity in CNMDU1 has a risk of severe progression, which makes early diagnosis by biopsy important. The surgery may be recommended before severe progression of spinal deformity and respiratory disorder. Perioperative MH is a concern, but can be managed by appropriate procedures.

Anesthetic case in a child with congenital neuromuscular disease with uniform type 1 fibers (CNMDU1)

Congenital neuromuscular disease with uniform type 1 fibers (CNMDU1) is an extremely rare, non-progressive, congenital neuromuscular disorder. Although the etiology is unknown, ryanodine receptor gene mutation is reportedly involved. No descriptions of anesthetic practice in patients with this disease have been reported around the world. We report a case of safe perioperative management with general anesthesia, using total intravenous anesthesia, propofol, fentanyl and a non-depolarizing muscle relaxant but avoiding the use of any inhaled anesthetics or depolarizing muscle relaxants to prevent malignant hyperthermia and postoperative respiratory failure, during anesthetic management for cranioplasty for premature synostosis of the cranial sutures in a pediatric patient of CNMDU1.

What is a waddling gait?

PURPOSE

A patient's gait can provide important diagnostic and functional information. Though 'waddling gait' is a long-established concept, we question whether this description is precise or clinically useful.

METHODS

We searched 'waddling gait' in all main medical specialties core textbooks, in animal locomotion books and in Medline, Healthstar and Embase. Further we obtained expert advice on the gait of ducks.

RESULTS

Many names are used for 'waddling gait', and its description is imprecise and inconsistent. Trendelenburg described it as a pelvic drop on the side of the swinging leg and compensatory lateral trunk bending towards the side of the standing leg. Many conditions have been described as producing a waddling gait. We accepted the gait pattern of ducks as being true waddling. This often-used comparison does not accurately reflect the gait pattern seen in humans with a range of medical disorders; nor is it the same as a Trendelenburg gait.

CONCLUSIONS

As we have found no condition in which patients have a truly duck-like gait, we propose that the phrase 'waddling gait' should be abandoned. We suggest that for clarity and good communication, clinicians should describe the observed elements of the gait rather than using imprecise and unhelpful terms such as 'waddling gait'.

A case of congenital neuromuscular disease with uniform type 1 fibers

Congenital neuromuscular disease with uniform type 1 fibers is a rare form of congenital nonprogressive myopathy. We report a 3-year-old boy with this disease who showed delayed motor developmental milestones and recurrent acute respiratory failure. He obtained head control at 16 months, crawled at 17 months and sat alone at 20 months, but still could not walk at age 44 months. His mental development was good; he could speak 3-word sentences at 44 months. Scoliosis, bilateral congenital dislocation of the hips, bilateral undescended testes and hemangioma simplex on the right lower limb were also seen. Muscle biopsy at the age of 8 months showed more than 99% of the myofibers were type 1. This is the first case of congenital neuromuscular disease with uniform type 1 fibers accompanied by recurrent acute respiratory failure. This case may be clinically more severe than previously reported cases.

Brain atrophy in congenital neuromuscular disease with uniform type 1 fibers

We report a patient with congenital neuromuscular disease with uniform type 1 fibers. The patient had manifested muscle weakness and running difficulty since early childhood. Ptosis and ophthalmoplegia were evident, in addition to facial and distal weakness. Her serum creatine kinase level was normal, and electromyography revealed low-amplitude and short duration of motor unit potentials. A muscle biopsy specimen demonstrated absolute predominance of type 1 fibers (> 98%) with no diagnostic structures. Her intelligence was borderline (IQ 80), and dilatation of the lateral ventricles was demonstrated by cranial CT. This is the first report of an abnormality in the central nervous system in congenital neuromuscular disease with uniform type 1 fibers.