Nemaline myopathy in a newborn infant: a rare muscle disorder

Abstract

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.

Nemaline rod myopathy treated with L-tyrosine to relieve symptoms in a neonate

“…The differential diagnosis between a primary central nervous system disorder and a neonatal muscle disorder requires a methodological approach including a detailed family, obstetric and delivery history and a careful examination. 8 Muscle biopsy is usually left as the last step of diagnostic tests, in the differential diagnosis of infantile hypotonicity. In the presented case, we could confirm the diagnosis by an eventual muscle biopsy after a thorough investigation of all the possible disorders with a stepwise approach.…”

“…13 On the other hand, there are few reports regarding the possible positive effect of L-tyrosine on decreasing secretions and increasing muscle strength. 7,8,14 Tyrosine is an aromatic amino acid derived in mammals from hydrolysis of dietary or tissue proteins or from hydroxylation of dietary or tissue phenylalanine. 15 But tyrosine is also the starting point of the synthetic pathways producing catecholamines, thyroid hormone, and the melanin pigments.…”

“…Improvement in muscle strength is also reported in several cases. 7,8 We present a newborn with severe respiratory failure and generalized muscle weakness, who was diagnosed as NM by muscle biopsy. The patient experienced remarkable decrease in drooling and improvement of spontaneous movements after L-tyrosine treatment.…”

L-tyrosine supplementation is not therapeutic for skeletal muscle dysfunction in zebrafish and mouse models of dominant skeletal muscle α-actin nemaline myopathy

“…Prior reports of L-tyrosine supplementation to NM patients describe potential positive effects of improved skeletal muscle strength, decreased pharyngeal/oral secretions, and increased stamina/energy levels (Kalita, 1989; Ryan et al, 2008; Olukman et al, 2013), but lacked sufficient numbers for statistical evaluation. The purpose of this study was to evaluate the therapeutic usefulness of L-tyrosine supplementation on one of these previously reported potential benefits, skeletal muscle function, using three dominant ACTA1 -NM animal models and multiple measures.…”

“…Within 72 h on the L-tyrosine regime, all infants displayed initial improvements in “sialorrhoea, skeletal muscle strength and energy levels” (Ryan et al, 2008). Additionally, L-tyrosine (250 mg/d) from 3 months of age was reported to produce marked reduction in oral secretions and improvement in skeletal muscle strength in a severely affected NM patient, however the patient died at 4 months with sudden cardiorespiratory failure (Olukman et al, 2013).…”