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Myopathy, congenital proximal, with minicore lesions(MYOPMIL; CMYP9B)

MedGen UID:
1717569
Concept ID:
C5394193
Disease or Syndrome
Synonyms: CMYP9B; CONGENITAL MYOPATHY 9B, PROXIMAL, WITH MINICORE LESIONS; MYOPATHY, CONGENITAL PROXIMAL, WITH MINICORE LESIONS; MYOPMIL
 
Gene (location): FXR1 (3q26.33)
 
Monarch Initiative: MONDO:0032937
OMIM®: 618823

Definition

Congenital myopathy-9B (CMYP9B) is an autosomal recessive early-onset skeletal muscle disorder mainly affecting proximal muscles. Affected individuals have neonatal hypotonia followed by mildly delayed walking in childhood. Muscle weakness is slowly progressive, resulting in positive Gowers sign and difficulty running or climbing, but most patients remain ambulatory. Some patients develop respiratory involvement requiring ventilatory support, whereas cardiac function is unaffected. Muscle biopsy shows type 1 fiber predominance with disorganized Z-lines and multiminicore myopathy (Estan et al., 2019). For a discussion of genetic heterogeneity of congenital myopathy, see CMYP1A (117000). [from OMIM]

Clinical features

From HPO
Cryptorchidism
MedGen UID:
8192
Concept ID:
C0010417
Congenital Abnormality
Cryptorchidism, or failure of testicular descent, is a common human congenital abnormality with a multifactorial etiology that likely reflects the involvement of endocrine, environmental, and hereditary factors. Cryptorchidism can result in infertility and increases risk for testicular tumors. Testicular descent from abdomen to scrotum occurs in 2 distinct phases: the transabdominal phase and the inguinoscrotal phase (summary by Gorlov et al., 2002).
Hypoplastic male external genitalia
MedGen UID:
338952
Concept ID:
C1852534
Finding
Underdevelopment of part or all of the male external reproductive organs (which include the penis, the scrotum and the urethra).
Areflexia
MedGen UID:
115943
Concept ID:
C0234146
Finding
Absence of neurologic reflexes such as the knee-jerk reaction.
Obstructive sleep apnea syndrome
MedGen UID:
101045
Concept ID:
C0520679
Disease or Syndrome
Obstructive sleep apnea is a common, chronic, complex disease associated with serious cardiovascular and neuropsychologic sequelae and with substantial social and economic costs (Palmer et al., 2003).
Motor delay
MedGen UID:
381392
Concept ID:
C1854301
Finding
A type of Developmental delay characterized by a delay in acquiring motor skills.
Proximal muscle weakness
MedGen UID:
113169
Concept ID:
C0221629
Finding
A lack of strength of the proximal muscles.
Centrally nucleated skeletal muscle fibers
MedGen UID:
330782
Concept ID:
C1842170
Finding
An abnormality in which the nuclei of sarcomeres take on an abnormally central localization (or in which this feature is found in an increased proportion of muscle cells).
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).
Neonatal hypotonia
MedGen UID:
412209
Concept ID:
C2267233
Disease or Syndrome
Muscular hypotonia (abnormally low muscle tone) manifesting in the neonatal period.
Z-band streaming
MedGen UID:
480908
Concept ID:
C3279278
Finding
Streaming or smearing of the Z band, which is then no longer confined to a narrow zone which bisects the I band. The Z disk may extend across the I band or the entire sarcomere in a zigzag manner. Focal thickening, smudging, and blurring of the Z band takes place concurrently. Myofibrillar disorganization is a frequent but not invariable accompanying change.
Fatty replacement of skeletal muscle
MedGen UID:
866735
Concept ID:
C4021082
Finding
Muscle fibers degeneration resulting in fatty replacement of skeletal muscle fibers
Minicore myopathy
MedGen UID:
961596
Concept ID:
CN279271
Disease or Syndrome
Multiple small zones of sarcomeric disorganization and lack of oxidative activity (known as minicores) in muscle fibers.
Tongue fasciculations
MedGen UID:
65987
Concept ID:
C0239548
Finding
Fasciculations or fibrillation affecting the tongue muscle.
Oligohydramnios
MedGen UID:
86974
Concept ID:
C0079924
Pathologic Function
Diminished amniotic fluid volume in pregnancy.
Decreased fetal movement
MedGen UID:
68618
Concept ID:
C0235659
Finding
An abnormal reduction in quantity or strength of fetal movements.

Recent clinical studies

Clinical prediction guides

Muelas N, Hackman P, Luque H, Garcés-Sánchez M, Azorín I, Suominen T, Sevilla T, Mayordomo F, Gómez L, Martí P, María Millán J, Udd B, Vílchez JJ
Neurology 2010 Aug 24;75(8):732-41. doi: 10.1212/WNL.0b013e3181eee4d5. PMID: 20733148

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