Congenital myopathy caused by a novel missense mutation in the CFL2 gene

Abstract

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.

Introduction

Congenital myopathies are a group of muscle disorders presenting early in life with floppiness due to muscle weakness. Other features include breathing or feeding difficulties and a delay in motor development. The most common type of congenital myopathy is nemaline myopathy (NM). NM is a clinically and genetically heterogeneous neuromuscular disorder of skeletal muscle thin filaments [1], [2], [3], [25]. The condition typically presents with skeletal muscle weakness and hypotonia, and is usually slowly or non-progressive. The clinical symptoms can range from mild weakness with onset ranging from birth to adulthood, to death in infancy in severe neonatal forms [4]. In the affected skeletal muscles, rodlike ‘nemaline body’ structures, resulting from abnormalities in the thin filaments, are the predominant finding [4], [24]. So far, mutations in seven different genes have been reported to cause NM, including one instance of a missense mutation in CFL2, a gene encoding the actin-binding protein cofilin-2 [2], [5], [6].

Myofibrillar myopathy (MFM) is another primary disease of skeletal muscle, characterized by variable degrees and patterns of muscle weakness that can be distal, limb-girdle or scapuloperoneal in distribution, or present as a generalized myopathy. This heterogeneous group of disorders also has a variable clinical presentation, but in contrast to NM, tends to be progressive. Most forms of MFM have their onset in adulthood and are usually autosomal dominant in inheritance. Pathologically MFM is characterized by distinctive features including myofibrillar dissolution with disintegration of the sarcomeric Z-line, accumulation of myofibrillar products and abnormal accumulation of proteins such as desmin, myotilin, dystrophin and others [19]. Mutations in several genes encoding for Z-line associated proteins have been identified in MFM, although a majority of cases are due to mutations in as yet unidentified genes [7], [8]. Due to its progressive clinical course and apparent primary degeneration and regeneration of myofibers, MFM is often considered a form of muscular dystrophy [8].

Here we report on the clinical and myopathological findings in two Iraqi Kurdish sisters with an autosomal recessive congenital myopathy consistent with NM as well as MFM due to a novel homozygous CFL2 missense mutation.

The proband is the first child of Iraqi Kurdish consanguineous parents (Fig. 1A–C) and was born at term by cesarean section due to a breech presentation. Her initial development was reportedly normal. She started to sit at the age of 6 months and to crawl when she was 11 months old. However, she did not walk until the age of 2 years and 6 months. Her maximum walking distance was a few hundred meters. Fine motor skills were intact. In Iraq, the diagnosis ‘progressive myopathy’ was made. By age 13, she had developed a severe kyphoscoliosis (Cobb angle of 60°, a kyphosis of 69°, and a torsion of 25° of pelvis and lumbar spine). Because of unforeseen problems, surgical correction had to be postponed and the kyphosis increased to 118° with a thoracolumbar scoliotic bend to the left of 57° and a compensatory angle of 44°. At the age of 15 years, the family had fled to the Netherlands and the patient was seen in our Neurology department. She complained about difficulties keeping her head straight and the need to support it with her hands. She reported reasonable arm strength but said her legs felt weak. The maximum walking distance was 50–100 m.

Neurological examination showed a girl with normal intelligence and social skills. Vision and hearing were normal. She had a high-arched palate, a very low-pitched voice and needed to support her head with her hands. Facial muscles showed a slight weakness, MRC grade 4, without involvement of the eye muscles. She had a fixated back and a cervical lordosis (Fig. 1A–C). The neck muscles were hypotonic with a paresis grade 2 of the flexor muscles and a paresis grade 4 of the extensor muscles. The shoulder girdle muscles had a paresis grade 2, whereas the rest of the arms showed a grade 4 weakness. For getting up, she used the Gowers’ manoeuvre. The strength of the iliopsoas muscles was an MRC grade 1, the other legs muscles had a paresis grade 3–4. The sensory exam was normal and reflexes were absent. The knees had a contracture of 10°. Routine hematological and chemical analysis was normal, the CK level at the age of 11 years was 134 U/l (normal). CT scanning of the limbs at the age of 12 years revealed fatty changes in a number of leg, trunk and arm muscles, most conspicuously in the soleus and quadriceps, but sparing the rectus femoris, and also of the semitendinosus, adductor magnus, serratus anterior and latissimus dorsi. Slight abnormalities were seen in the gluteals and peroneal muscles, largely sparing the tibialis anterior. Unfortunately the scan quality was insufficient to examine the upper extremity muscles, due to movement artefacts. Nerve latencies and conduction velocities were normal on EMG examination. Needle examination revealed fibrillations and positive spikes with small low amplitude polyphasic motor units with an increased recruitment pattern. The ear, nose and throat specialist concluded that the low-pitched voice was due to her posture. No cardiac abnormalities were found with echocardiography.

In the following years, a gradual decline of strength was noted. Her ability to walk had decreased to a few meters indoors and the head drop increased. As she complained of shortness of breath on occasions, pulmonary function tests were done. This revealed a chronic respiratory insufficiency due to muscle weakness. Non-invasive nocturnal positive pressure ventilation was initiated, resulting in an improvement of her general physical condition. At the age of 21 years she is completely wheelchair dependent, but studies architecture and enjoys an active social life.

The proband’s sister was also born at term by cesarean section because of a breech presentation. Because of her affected sibling, neurological examination was performed in the neonatal period, but no abnormalities were seen until the age of 2 years and 7 months. From that moment, she started to lag in motor development. Neurological examination at that time showed hypotonia, hyperextension of the knees and elbows, and a waddling gait. Gowers’ sign was positive. Although due to lack of cooperation formal muscle strength testing was not possible, no obvious facial and shoulder weakness was seen. She had a lumbar lordosis and pes planes (Fig 1D–F). Cardiac examination was normal and routine hematological and chemical analysis showed no abnormalities. EMG revealed normal motor and sensory conduction velocities, and amplitudes. Due to lack of cooperation, needle examination was limited to the rectus femoris muscle which showed no abnormalities. Quantitative muscle ultrasound [9] showed abnormal echo intensities in all extremities (Fig. 2). Because an autosomal recessive inheritance was suspected, the family was referred to the clinical geneticist (see Section 3).

At the most recent follow-up at the age of 5 years, the parents reported that she had more difficulties with keeping her head straight with an occasional head drop backwards. Running skills have improved slightly but she stumbled regularly. Examination showed a girl with normal intelligence. Muscle strength testing showed weakness MRC grade 2 of the neck flexors, axial muscles, hip abductor, and periscapular muscles, and a weakness grade 4 of the hip flexors, biceps and distal muscles.

Family history showed no other affected family members. The paternal grandfather of the mother was a sibling of the father’s mother (Fig. 3).