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Nemaline myopathy 5B, autosomal recessive, childhood-onset(NEM5B)

MedGen UID:
1841181
Concept ID:
C5830545
Disease or Syndrome
Synonym: NEM5B
 
Gene (location): TNNT1 (19q13.42)
 
Monarch Initiative: MONDO:0957281
OMIM®: 620386

Definition

Autosomal recessive childhood-onset nemaline myopathy-5B (NEM5B) is a skeletal muscle disorder in which patients usually present with proximal muscle weakness of the lower and upper limbs in a limb-girdle distribution, resulting in gait abnormalities; however, most remain ambulatory even into late adulthood. Some affected individuals show delayed motor development. There is axial weakness and atrophy of the paraspinal muscles, along with kyphosis, scoliosis, and rigid spine, as well as variable limitations of the large joints. Most patients develop restrictive respiratory insufficiency with decreased forced vital capacity; some need noninvasive ventilation. Serum creatine kinase may be elevated. Muscle biopsy can show variable features, including nemaline rods, multiminicore lesions, endomysial fibrosis, and myofibrillar changes (Pellerin et al., 2020; Lee et al., 2022). For a discussion of genetic heterogeneity of nemaline myopathy, see NEM2 (256030). [from OMIM]

Clinical features

From HPO
Ankle contracture
MedGen UID:
575402
Concept ID:
C0343148
Acquired Abnormality
Limb-girdle muscle weakness
MedGen UID:
347625
Concept ID:
C1858127
Finding
Weakness of the limb-girdle muscles (also known as the pelvic and shoulder girdles), that is, lack of strength of the muscles around the shoulders and the pelvis.
Fatty replacement of ventricular myocardial tissue
MedGen UID:
1614677
Concept ID:
C4531204
Pathologic Function
Presence of an increased amount of fat tissue within a cardiac ventricle with corresponding reduction of muscle tissue.
Delayed gross motor development
MedGen UID:
332508
Concept ID:
C1837658
Finding
A type of motor delay characterized by a delay in acquiring the ability to control the large muscles of the body for walking, running, sitting, and crawling.
Rhabdomyolysis
MedGen UID:
19775
Concept ID:
C0035410
Pathologic Function
Breakdown of muscle fibers that leads to the release of muscle fiber contents (myoglobin) into the bloodstream.
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.
Gowers sign
MedGen UID:
65865
Concept ID:
C0234182
Finding
A phenomenon whereby patients are not able to stand up without the use of the hands owing to weakness of the proximal muscles of the lower limbs.
Difficulty climbing stairs
MedGen UID:
68676
Concept ID:
C0239067
Finding
Reduced ability to climb stairs.
Wrist flexion contracture
MedGen UID:
592338
Concept ID:
C0409345
Acquired Abnormality
A chronic loss of wrist joint motion due to structural changes in muscle, tendons, ligaments, or skin that prevent normal movement of the joints of the wrist.
Hip contracture
MedGen UID:
140815
Concept ID:
C0409354
Acquired Abnormality
Lack of full passive range of motion (restrictions in flexion, extension, or other movements) of the hip joint resulting from structural changes of non-bony tissues, such as muscles, tendons, ligaments, joint capsules and/or skin.
Kyphoscoliosis
MedGen UID:
154361
Concept ID:
C0575158
Anatomical Abnormality
An abnormal curvature of the spine in both a coronal (lateral) and sagittal (back-to-front) plane.
Elbow contracture
MedGen UID:
331445
Concept ID:
C1833142
Anatomical Abnormality
A limitation in the passive range of motion of the elbow resulting from loss of elasticity in the periarticular tissues owing to structural changes of non-bony tissues, such as muscles, tendons, ligaments, joint capsules or skin.
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.
Congenital multicore myopathy with external ophthalmoplegia
MedGen UID:
340597
Concept ID:
C1850674
Disease or Syndrome
Congenital myopathy-1B (CMYO1B) is an autosomal recessive disorder of skeletal muscle characterized by severe hypotonia and generalized muscle weakness apparent soon after birth or in early childhood with delayed motor development, generalized muscle weakness and atrophy, and difficulty walking or running. Affected individuals show proximal muscle weakness with axial and shoulder girdle involvement, external ophthalmoplegia, and bulbar weakness, often resulting in feeding difficulties and respiratory insufficiency. Orthopedic complications such as joint laxity, distal contractures, hip dislocation, cleft palate, and scoliosis are commonly observed. Serum creatine kinase is normal. The phenotype is variable in severity (Jungbluth et al., 2005; Bharucha-Goebel et al., 2013). Some patients show symptoms in utero, including reduced fetal movements, polyhydramnios, and intrauterine growth restriction. The most severely affected patients present in utero with fetal akinesia, arthrogryposis, and lung hypoplasia resulting in fetal or perinatal death (McKie et al., 2014). Skeletal muscle biopsy of patients with recessive RYR1 mutations can show variable features, including multiminicores (Ferreiro and Fardeau, 2002), central cores (Jungbluth et al., 2002), congenital fiber-type disproportion (CFTD) (Monnier et al., 2009), and centronuclear myopathy (Wilmshurst et al., 2010). For a discussion of genetic heterogeneity of congenital myopathy, see CMYO1A (117000).
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.
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.
Reduced forced vital capacity
MedGen UID:
337630
Concept ID:
C1846678
Finding
An abnormal reduction in the amount of air a person can expel following maximal inspiration.
Elevated circulating creatine kinase concentration
MedGen UID:
69128
Concept ID:
C0241005
Finding
An elevation of the level of the enzyme creatine kinase (also known as creatine phosphokinase (CK; EC 2.7.3.2) in the blood. CK levels can be elevated in a number of clinical disorders such as myocardial infarction, rhabdomyolysis, and muscular dystrophy.

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