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Nemaline myopathy 2(NEM2)

MedGen UID:
342534
Concept ID:
C1850569
Disease or Syndrome
Synonyms: NEM2; Nemaline myopathy 2, autosomal recessive; Nemaline myopathy caused by mutation in the nebulin gene
 
Gene (location): NEB (2q23.3)
 
Monarch Initiative: MONDO:0009725
OMIM®: 256030

Definition

Nemaline myopathy-2 (NEM2) is an autosomal recessive skeletal muscle disorder with a wide range of severity. The most common clinical presentation is early-onset (in infancy or childhood) muscle weakness predominantly affecting proximal limb muscles. Muscle biopsy shows accumulation of Z-disc and thin filament proteins into aggregates named 'nemaline bodies' or 'nemaline rods,' usually accompanied by disorganization of the muscle Z discs. The clinical and histologic spectrum of entities caused by variants in the NEB gene is a continuum, ranging in severity. The distribution of weakness can vary from generalized muscle weakness, more pronounced in proximal limb muscles, to distal-only involvement, although neck flexor weakness appears to be rather consistent. Histologic patterns range from a severe usually nondystrophic disturbance of the myofibrillar pattern to an almost normal pattern, with or without nemaline bodies, sometimes combined with cores (summary by Lehtokari et al., 2014). Genetic Heterogeneity of Nemaline Myopathy See also NEM1 (255310), caused by mutation in the tropomyosin-3 gene (TPM3; 191030) on chromosome 1q22; NEM3 (161800), caused by mutation in the alpha-actin-1 gene (ACTA1; 102610) on chromosome 1q42; NEM4 (609285), caused by mutation in the beta-tropomyosin gene (TPM2; 190990) on chromosome 9p13; NEM5A (605355), also known as Amish nemaline myopathy, NEM5B (620386), and NEM5C (620389), all caused by mutation in the troponin T1 gene (TNNT1; 191041) on chromosome 19q13; NEM6 (609273), caused by mutation in the KBTBD13 gene (613727) on chromosome 15q22; NEM7 (610687), caused by mutation in the cofilin-2 gene (CFL2; 601443) on chromosome 14q13; NEM8 (615348), caused by mutation in the KLHL40 gene (615340), on chromosome 3p22; NEM9 (615731), caused by mutation in the KLHL41 gene (607701) on chromosome 2q31; NEM10 (616165), caused by mutation in the LMOD3 gene (616112) on chromosome 3p14; and NEM11 (617336), caused by mutation in the MYPN gene (608517) on chromosome 10q21. Several of the genes encode components of skeletal muscle sarcomeric thin filaments (Sanoudou and Beggs, 2001). Mutations in the NEB gene are the most common cause of nemaline myopathy (Lehtokari et al., 2006). [from OMIM]

Additional description

From MedlinePlus Genetics
Nemaline myopathy is a disorder that primarily affects skeletal muscles, which are muscles that the body uses for movement. People with nemaline myopathy have muscle weakness (myopathy) throughout the body, but it is typically most severe in the muscles of the face; neck; trunk; and other muscles close to the center of the body (proximal muscles), such as those of the upper arms and legs. This weakness can worsen over time. Affected individuals may have feeding and swallowing difficulties, foot deformities, abnormal curvature of the spine (scoliosis), and joint deformities (contractures). Most people with nemaline myopathy are able to walk, although some affected children may begin walking later than usual. As the condition progresses, some people may require wheelchair assistance. In severe cases, the muscles used for breathing are affected and life-threatening breathing difficulties can occur.

Nemaline myopathy is divided into six types. In order of decreasing severity, the types are: severe congenital, Amish, intermediate congenital, typical congenital, childhood-onset, and adult-onset. The types are distinguished by the age when symptoms first appear and the severity of symptoms; however, there is overlap among the various types. The severe congenital type is the most life-threatening. Most individuals with this type do not survive past early childhood due to respiratory failure. The Amish type solely affects the Old Order Amish population of Pennsylvania and is typically fatal in early childhood. The most common type of nemaline myopathy is the typical congenital type, which is characterized by muscle weakness and feeding problems beginning in infancy. Most of these individuals do not have severe breathing problems and can walk unassisted. People with the childhood-onset type usually develop muscle weakness in adolescence. The adult-onset type is the mildest of all the various types. People with this type usually develop muscle weakness between ages 20 and 50.  https://medlineplus.gov/genetics/condition/nemaline-myopathy

Clinical features

From HPO
Hand clenching
MedGen UID:
65994
Concept ID:
C0239815
Finding
An abnormal hand posture in which the hands are clenched to fists. All digits held completely flexed at the metacarpophalangeal and interphalangeal joints. In prenatal sonography of the fetal clenched hand, the index finger overlaps a clenched fist formed by the other digits. The proximal interphalangeal articulation of the index finger is flexed and ulnarly deviated, and the thumb is adducted.
Limb muscle weakness
MedGen UID:
107956
Concept ID:
C0587246
Finding
Reduced strength and weakness of the muscles of the arms and legs.
Talipes
MedGen UID:
220976
Concept ID:
C1301937
Congenital Abnormality
A deformity of foot and ankle that has different subtypes that are talipes equinovarus, talipes equinovalgus, talipes calcaneovarus and talipes calcaneovalgus.
Calf muscle pseudohypertrophy
MedGen UID:
374276
Concept ID:
C1839666
Finding
Enlargement of the muscles of the calf due to their replacement by connective tissue or fat.
Foot dorsiflexor weakness
MedGen UID:
356163
Concept ID:
C1866141
Finding
Weakness of the muscles responsible for dorsiflexion of the foot, that is, of the movement of the toes towards the shin. The foot dorsiflexors include the tibialis anterior, the extensor hallucis longus, the extensor digitorum longus, and the peroneus tertius muscles.
Slender build
MedGen UID:
376828
Concept ID:
C1850573
Finding
Asthenic habitus refers to a slender build with long limbs, an angular profile, and prominent muscles or bones.
Dysphagia
MedGen UID:
41440
Concept ID:
C0011168
Disease or Syndrome
Difficulty in swallowing.
Feeding difficulties
MedGen UID:
65429
Concept ID:
C0232466
Finding
Impaired ability to eat related to problems gathering food and getting ready to suck, chew, or swallow it.
Low-set ears
MedGen UID:
65980
Concept ID:
C0239234
Congenital Abnormality
Upper insertion of the ear to the scalp below an imaginary horizontal line drawn between the inner canthi of the eye and extending posteriorly to the ear.
Dysarthria
MedGen UID:
8510
Concept ID:
C0013362
Mental or Behavioral Dysfunction
Dysarthric speech is a general description referring to a neurological speech disorder characterized by poor articulation. Depending on the involved neurological structures, dysarthria may be further classified as spastic, flaccid, ataxic, hyperkinetic and hypokinetic, or mixed.
Waddling gait
MedGen UID:
66667
Concept ID:
C0231712
Finding
Weakness of the hip girdle and upper thigh muscles, for instance in myopathies, leads to an instability of the pelvis on standing and walking. If the muscles extending the hip joint are affected, the posture in that joint becomes flexed and lumbar lordosis increases. The patients usually have difficulties standing up from a sitting position. Due to weakness in the gluteus medius muscle, the hip on the side of the swinging leg drops with each step (referred to as Trendelenburg sign). The gait appears waddling. The patients frequently attempt to counteract the dropping of the hip on the swinging side by bending the trunk towards the side which is in the stance phase (in the German language literature this is referred to as Duchenne sign). Similar gait patterns can be caused by orthopedic conditions when the origin and the insertion site of the gluteus medius muscle are closer to each other than normal, for instance due to a posttraumatic elevation of the trochanter or pseudarthrosis of the femoral neck.
Areflexia
MedGen UID:
115943
Concept ID:
C0234146
Finding
Absence of neurologic reflexes such as the knee-jerk reaction.
Steppage gait
MedGen UID:
98105
Concept ID:
C0427149
Finding
An abnormal gait pattern that arises from weakness of the pretibial and peroneal muscles due to a lower motor neuron lesion. Affected patients have footdrop and are unable to dorsiflex and evert the foot. The leg is lifted high on walking so that the toes clear the ground, and there may be a slapping noise when the foot strikes the ground again.
Inability to walk
MedGen UID:
107860
Concept ID:
C0560046
Finding
Incapability to ambulate.
Gait disturbance
MedGen UID:
107895
Concept ID:
C0575081
Finding
The term gait disturbance can refer to any disruption of the ability to walk. In general, this can refer to neurological diseases but also fractures or other sources of pain that is triggered upon walking. However, in the current context gait disturbance refers to difficulty walking on the basis of a neurological or muscular disease.
Hyporeflexia
MedGen UID:
195967
Concept ID:
C0700078
Finding
Reduction of neurologic reflexes such as the knee-jerk reaction.
Easy fatigability
MedGen UID:
373253
Concept ID:
C1837098
Finding
Increased susceptibility to fatigue.
Motor delay
MedGen UID:
381392
Concept ID:
C1854301
Finding
A type of Developmental delay characterized by a delay in acquiring motor skills.
Bulbar palsy
MedGen UID:
898626
Concept ID:
C4082299
Disease or Syndrome
Bulbar weakness (or bulbar palsy) refers to bilateral impairment of function of the lower cranial nerves IX, X, XI and XII, which occurs due to lower motor neuron lesion either at nuclear or fascicular level in the medulla or from bilateral lesions of the lower cranial nerves outside the brain-stem. Bulbar weakness is often associated with difficulty in chewing, weakness of the facial muscles, dysarthria, palatal weakness and regurgitation of fluids, dysphagia, and dysphonia.
Hyperlordosis
MedGen UID:
9805
Concept ID:
C0024003
Finding
Abnormally increased curvature (anterior concavity) of the lumbar or cervical spine.
Scoliosis
MedGen UID:
11348
Concept ID:
C0036439
Disease or Syndrome
The presence of an abnormal lateral curvature of the spine.
Proximal muscle weakness
MedGen UID:
113169
Concept ID:
C0221629
Finding
A lack of strength of the proximal muscles.
Congenital contracture
MedGen UID:
83066
Concept ID:
C0332878
Congenital Abnormality
One or more flexion contractures (a bent joint that cannot be straightened actively or passively) that are present at birth.
Flexion contracture
MedGen UID:
83069
Concept ID:
C0333068
Anatomical Abnormality
A flexion contracture is a bent (flexed) joint that cannot be straightened actively or passively. It is thus a chronic loss of joint motion due to structural changes in muscle, tendons, ligaments, or skin that prevents normal movement of joints.
Weakness of facial musculature
MedGen UID:
98103
Concept ID:
C0427055
Disease or Syndrome
Reduced strength of one or more muscles innervated by the facial nerve (the seventh cranial nerve).
Skeletal muscle atrophy
MedGen UID:
892680
Concept ID:
C0541794
Pathologic Function
The presence of skeletal muscular atrophy (which is also known as amyotrophy).
Generalized muscle weakness
MedGen UID:
155433
Concept ID:
C0746674
Sign or Symptom
Generalized weakness or decreased strength of the muscles, affecting both distal and proximal musculature.
Frequent falls
MedGen UID:
163408
Concept ID:
C0850703
Finding
Muscle fiber splitting
MedGen UID:
322813
Concept ID:
C1836057
Finding
Fiber splitting or branching is a common finding in human and rat skeletal muscle pathology. Fiber splitting refers to longitudinal halving of the complete fiber, while branching originates from a regenerating end of a necrotic fiber as invaginations of the sarcolemma. In fiber branching, one end of the fiber remains intact as a single entity, while the other end has several branches.
Neck flexor weakness
MedGen UID:
334801
Concept ID:
C1843637
Finding
Weakness of the muscles involved in neck flexion (sternocleidomastoid, longus capitus, longus colli, and scalenus anterior).
Increased variability in muscle fiber diameter
MedGen UID:
336019
Concept ID:
C1843700
Finding
An abnormally high degree of muscle fiber size variation. This phenotypic feature can be observed upon muscle biopsy.
Rimmed vacuoles
MedGen UID:
340089
Concept ID:
C1853932
Finding
Presence of abnormal vacuoles (membrane-bound organelles) in the sarcolemma. On histological staining with hematoxylin and eosin, rimmed vacuoles are popcorn-like clear vacuoles with a densely blue rim. The vacuoles are often associated with cytoplasmic and occasionally intranuclear eosinophilic inclusions.
Type 1 muscle fiber predominance
MedGen UID:
344274
Concept ID:
C1854387
Finding
An abnormal predominance of type I muscle fibers (in general, this feature can only be observed on muscle biopsy).
Spinal rigidity
MedGen UID:
346721
Concept ID:
C1858025
Finding
Reduced ability to move the vertebral column with a resulting limitation of neck and trunk flexion.
Thenar muscle atrophy
MedGen UID:
355274
Concept ID:
C1864715
Finding
Wasting of thenar muscles, which are located on palm of the hand at the base of the thumb.
Neonatal hypotonia
MedGen UID:
412209
Concept ID:
C2267233
Disease or Syndrome
Muscular hypotonia (abnormally low muscle tone) manifesting in the neonatal period.
Nemaline bodies
MedGen UID:
814369
Concept ID:
C3808039
Finding
Nemaline rods are abnormal bodies that can occur in skeletal muscle fibers. The rods can be observed on histological analysis of muscle biopsy tissue or upon electron microscopy, where they appear either as extensions of sarcomeric Z-lines, in random array without obvious attachment to Z-lines (often in areas devoid of sarcomeres) or in large clusters localized at the sarcolemma or intermyofibrillar spaces.
Fatty replacement of skeletal muscle
MedGen UID:
866735
Concept ID:
C4021082
Finding
Muscle fibers degeneration resulting in fatty replacement of skeletal muscle fibers
EMG: myopathic abnormalities
MedGen UID:
867362
Concept ID:
C4021726
Pathologic Function
The presence of abnormal electromyographic patterns indicative of myopathy, such as small-short polyphasic motor unit potentials.
EMG: neuropathic changes
MedGen UID:
867363
Concept ID:
C4021727
Finding
The presence of characteristic findings of denervation on electromyography (fibrillations, positive sharp waves, and giant motor unit potentials).
Sternocleidomastoid amyotrophy
MedGen UID:
868665
Concept ID:
C4023067
Disease or Syndrome
Wasting of the sternocleidomastoid muscle, the muscle in the anterior part of the neck that acts to flex and rotate the head.
Late-onset distal muscle weakness
MedGen UID:
871100
Concept ID:
C4025565
Finding
Abnormal rib cage morphology
MedGen UID:
871275
Concept ID:
C4025763
Anatomical Abnormality
A morphological anomaly of the rib cage.
Arthrogryposis multiplex congenita
MedGen UID:
1830310
Concept ID:
C5779613
Disease or Syndrome
Multiple congenital contractures in different body areas.
Apnea
MedGen UID:
2009
Concept ID:
C0003578
Sign or Symptom
Lack of breathing with no movement of the respiratory muscles and no exchange of air in the lungs. This term refers to a disposition to have recurrent episodes of apnea rather than to a single event.
Respiratory insufficiency due to muscle weakness
MedGen UID:
812797
Concept ID:
C3806467
Finding
Mildly elevated creatine kinase
MedGen UID:
342469
Concept ID:
C1850309
Finding
Narrow mouth
MedGen UID:
44435
Concept ID:
C0026034
Congenital Abnormality
Distance between the commissures of the mouth more than 2 SD below the mean. Alternatively, an apparently decreased width of the oral aperture (subjective).
High palate
MedGen UID:
66814
Concept ID:
C0240635
Congenital Abnormality
Height of the palate more than 2 SD above the mean (objective) or palatal height at the level of the first permanent molar more than twice the height of the teeth (subjective).
Myopathic facies
MedGen UID:
90695
Concept ID:
C0332615
Finding
A facial appearance characteristic of myopathic conditions. The face appears expressionless with sunken cheeks, bilateral ptosis, and inability to elevate the corners of the mouth, due to muscle weakness.
Long philtrum
MedGen UID:
351278
Concept ID:
C1865014
Finding
Distance between nasal base and midline upper lip vermilion border more than 2 SD above the mean. Alternatively, an apparently increased distance between nasal base and midline upper lip vermilion border.
Cleft palate
MedGen UID:
756015
Concept ID:
C2981150
Congenital Abnormality
Cleft palate is a developmental defect of the palate resulting from a failure of fusion of the palatine processes and manifesting as a separation of the roof of the mouth (soft and hard palate).
Polyhydramnios
MedGen UID:
6936
Concept ID:
C0020224
Pathologic Function
The presence of excess amniotic fluid in the uterus during pregnancy.
Decreased fetal movement
MedGen UID:
68618
Concept ID:
C0235659
Finding
An abnormal reduction in quantity or strength of fetal movements.
Hypertelorism
MedGen UID:
9373
Concept ID:
C0020534
Finding
Although hypertelorism means an excessive distance between any paired organs (e.g., the nipples), the use of the word has come to be confined to ocular hypertelorism. Hypertelorism occurs as an isolated feature and is also a feature of many syndromes, e.g., Opitz G syndrome (see 300000), Greig cephalopolysyndactyly (175700), and Noonan syndrome (163950) (summary by Cohen et al., 1995).
Abnormality of the eye
MedGen UID:
1370071
Concept ID:
C4316870
Anatomical Abnormality
Any abnormality of the eye, including location, spacing, and intraocular abnormalities.
Mitochondrial depletion
MedGen UID:
868267
Concept ID:
C4022659
Finding
An abnormal reduction in mitochondrial DNA content of cells.

Professional guidelines

Curated

Nowak KJ, Davis MR, Wallgren-Pettersson C, Lamont PJ, Laing NG
Eur J Hum Genet 2012 Jun;20(6) Epub 2012 Apr 18 doi: 10.1038/ejhg.2012.70. PMID: 22510848Free PMC Article

Recent clinical studies

Etiology

Gajda A, Horváth E, Hortobágyi T, Gergev G, Szabó H, Farkas K, Nagy N, Széll M, Sztriha L
J Child Neurol 2015 Apr;30(5):627-30. Epub 2013 Sep 20 doi: 10.1177/0883073813494476. PMID: 24056153
Chahin N, Selcen D, Engel AG
Neurology 2005 Oct 25;65(8):1158-64. Epub 2005 Sep 7 doi: 10.1212/01.wnl.0000180362.90078.dc. PMID: 16148261

Diagnosis

Wen Q, Chang X, Guo J
Acta Neurol Belg 2020 Dec;120(6):1351-1360. Epub 2019 Nov 6 doi: 10.1007/s13760-019-01230-3. PMID: 31696431
Chahin N, Selcen D, Engel AG
Neurology 2005 Oct 25;65(8):1158-64. Epub 2005 Sep 7 doi: 10.1212/01.wnl.0000180362.90078.dc. PMID: 16148261
Wallgren-Pettersson C, Laing N
Neuromuscul Disord 1996 Oct;6(5):389-91. doi: 10.1016/0960-8966(96)00354-9. PMID: 8938704

Prognosis

Chahin N, Selcen D, Engel AG
Neurology 2005 Oct 25;65(8):1158-64. Epub 2005 Sep 7 doi: 10.1212/01.wnl.0000180362.90078.dc. PMID: 16148261

Clinical prediction guides

Dumevska B, McKernan R, Goel D, Schmidt U
Stem Cell Res 2016 Mar;16(2):443-5. Epub 2016 Feb 11 doi: 10.1016/j.scr.2016.02.016. PMID: 27346011
Dumevska B, McKernan R, Goel D, Schmidt U
Stem Cell Res 2016 Mar;16(2):440-2. Epub 2016 Feb 11 doi: 10.1016/j.scr.2016.02.015. PMID: 27346010
Dumevska B, Main H, McKernan R, Goel D, Schmidt U
Stem Cell Res 2016 Mar;16(2):427-9. Epub 2016 Feb 3 doi: 10.1016/j.scr.2016.02.004. PMID: 27346006
Chahin N, Selcen D, Engel AG
Neurology 2005 Oct 25;65(8):1158-64. Epub 2005 Sep 7 doi: 10.1212/01.wnl.0000180362.90078.dc. PMID: 16148261

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