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Infantile-onset X-linked spinal muscular atrophy(SMAX2; AMCX1; XLSMA)

MedGen UID:
337123
Concept ID:
C1844934
Disease or Syndrome
Synonyms: AMC, distal, X-linked; Arthrogryposis multiplex congenita, distal, X-linked; ARTHROGRYPOSIS, X-LINKED, TYPE I; Spinal muscular atrophy, X-linked 2; Spinal Muscular Atrophy, X-Linked Infantile; SPINAL MUSCULAR ATROPHY, X-LINKED LETHAL INFANTILE
SNOMED CT: X-linked distal arthrogryposis multiplex congenita (719836007); Spinal muscular atrophy with arthrogryposis (719836007); X-linked spinal muscular atrophy type 2 (719836007); Infantile-onset X-linked spinal muscular atrophy (719836007)
Modes of inheritance:
X-linked recessive inheritance
MedGen UID:
375779
Concept ID:
C1845977
Finding
Source: Orphanet
A mode of inheritance that is observed for recessive traits related to a gene encoded on the X chromosome. In the context of medical genetics, X-linked recessive disorders manifest in males (who have one copy of the X chromosome and are thus hemizygotes), but generally not in female heterozygotes who have one mutant and one normal allele.
 
Gene (location): UBA1 (Xp11.3)
 
Monarch Initiative: MONDO:0010532
OMIM®: 301830
Orphanet: ORPHA1145

Disease characteristics

Excerpted from the GeneReview: Spinal Muscular Atrophy, X-Linked Infantile
X-linked infantile spinal muscular atrophy (XL-SMA) is characterized by congenital hypotonia, areflexia, and evidence of degeneration and loss of anterior horn cells (i.e., lower motor neurons) in the spinal cord and brain stem. Often congenital contractures and/or fractures are present. Intellect is normal. Life span is significantly shortened because of progressive ventilatory insufficiency resulting from chest muscle involvement. [from GeneReviews]
Authors:
Lisa Baumbach-Reardon  |  JM Hunter  |  Mary Ellen Ahearn, et. al.   view full author information

Additional descriptions

From OMIM
X-linked spinal muscular atrophy-2 (SMAX2) is characterized by neonatal onset of severe hypotonia, areflexia, and multiple congenital contractures, known as arthrogryposis, associated with loss of anterior horn cells and infantile death (summary by Ramser et al., 2008). Historically, Hall et al. (1982) distinguished at least 3 clinical varieties of X-linked arthrogryposis. (1) One family had a severe lethal form with severe contractures, scoliosis, chest deformities, hypotonia, micrognathia, and death from respiratory insufficiency by age 3 months. Apparently progressive loss of anterior horn cells was the cause. (2) Two families had moderately severe AMC associated with ptosis, microphallus, cryptorchidism, inguinal hernias, and normal intelligence. Nonprogressive intrauterine myopathy appeared to be the 'cause'. (3) In 2 families and a sporadic case, the disorder took the form of a resolving AMC, with mild to moderate contractures improving dramatically with time, normal intelligence, and no other anomalies; tight connective tissues on misplaced tendons was postulated.  http://www.omim.org/entry/301830
From MedlinePlus Genetics
X-linked infantile spinal muscular atrophy is a condition that affects only boys and is characterized by severe muscle weakness and absent reflexes (areflexia). Affected children often have multiple joint deformities (contractures) from birth that cause joint stiffness (arthrogryposis) and impair movement. In severe cases, affected infants are born with broken bones. The muscle weakness worsens over time; affected children reach some early motor developmental milestones, such as sitting unassisted, but these skills are often lost (developmental regression).

Additional features of X-linked infantile spinal muscular atrophy include an unusually small chin (micrognathia), abnormal curvature of the spine (scoliosis or kyphosis), and undescended testes (cryptorchidism).

Weakness of the chest muscles used for breathing often leads to life-threatening breathing problems. Children with X-linked infantile spinal muscular atrophy usually do not survive past early childhood due to respiratory failure, although, in rare cases, affected individuals can survive into adolescence.  https://medlineplus.gov/genetics/condition/x-linked-infantile-spinal-muscular-atrophy

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).
Hypospadias
MedGen UID:
163083
Concept ID:
C0848558
Congenital Abnormality
Abnormal position of urethral meatus on the ventral penile shaft (underside) characterized by displacement of the urethral meatus from the tip of the glans penis to the ventral surface of the penis, scrotum, or perineum.
Micropenis
MedGen UID:
1633603
Concept ID:
C4551492
Congenital Abnormality
Abnormally small penis. At birth, the normal penis is about 3 cm (stretched length from pubic tubercle to tip of penis) with micropenis less than 2.0-2.5 cm.
Areflexia
MedGen UID:
115943
Concept ID:
C0234146
Finding
Absence of neurologic reflexes such as the knee-jerk reaction.
Persistent head lag
MedGen UID:
256151
Concept ID:
C1141883
Finding
The Premie-Neuro and the Dubowitz Neurological Examination score head lag in the same manner. Scoring for both is as follows
Degeneration of anterior horn cells
MedGen UID:
375215
Concept ID:
C1843505
Finding
Decreased compound muscle action potential amplitude
MedGen UID:
908357
Concept ID:
C4230625
Finding
Reduced level of the compound muscle action potential (CMAP), which is recorded following electrical stimulation of a nerve from surface electrodes overlying a muscle supplied by that nerve.
Inguinal hernia
MedGen UID:
6817
Concept ID:
C0019294
Finding
Protrusion of the contents of the abdominal cavity through the inguinal canal.
Micrognathia
MedGen UID:
44428
Concept ID:
C0025990
Congenital Abnormality
Developmental hypoplasia of the mandible.
Hypotonia
MedGen UID:
10133
Concept ID:
C0026827
Finding
Hypotonia is an abnormally low muscle tone (the amount of tension or resistance to movement in a muscle). Even when relaxed, muscles have a continuous and passive partial contraction which provides some resistance to passive stretching. Hypotonia thus manifests as diminished resistance to passive stretching. Hypotonia is not the same as muscle weakness, although the two conditions can co-exist.
Spinal muscular atrophy
MedGen UID:
7755
Concept ID:
C0026847
Disease or Syndrome
Spinal muscular atrophy (SMA) is characterized by muscle weakness and atrophy resulting from progressive degeneration and irreversible loss of the anterior horn cells in the spinal cord (i.e., lower motor neurons) and the brain stem nuclei. The onset of weakness ranges from before birth to adulthood. The weakness is symmetric, proximal > distal, and progressive. Before the genetic basis of SMA was understood, it was classified into clinical subtypes based on maximum motor function achieved; however, it is now apparent that the phenotype of SMN1-associated SMA spans a continuum without clear delineation of subtypes. With supportive care only, poor weight gain with growth failure, restrictive lung disease, scoliosis, and joint contractures are common complications; however, newly available targeted treatment options are changing the natural history of this disease.
Myopathy
MedGen UID:
10135
Concept ID:
C0026848
Disease or Syndrome
A disorder of muscle unrelated to impairment of innervation or neuromuscular junction.
Scoliosis
MedGen UID:
11348
Concept ID:
C0036439
Disease or Syndrome
The presence of an abnormal lateral curvature of the spine.
Multiple joint contractures
MedGen UID:
57633
Concept ID:
C0158118
Acquired Abnormality
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.
Facial palsy
MedGen UID:
87660
Concept ID:
C0376175
Disease or Syndrome
Facial nerve palsy is a dysfunction of cranial nerve VII (the facial nerve) that results in inability to control facial muscles on the affected side with weakness of the muscles of facial expression and eye closure. This can either be present in unilateral or bilateral form.
Severe muscular hypotonia
MedGen UID:
326544
Concept ID:
C1839630
Finding
A severe degree of muscular hypotonia characterized by markedly reduced muscle tone.
Arthrogryposis multiplex congenita
MedGen UID:
1830310
Concept ID:
C5779613
Disease or Syndrome
Multiple congenital contractures in different body areas.
Respiratory insufficiency
MedGen UID:
11197
Concept ID:
C0035229
Pathologic Function
Impairment of gas exchange within the lungs secondary to a disease process, neoplasm, or trauma, possibly resulting in hypoxia, hypercarbia, or both, but not requiring intubation or mechanical ventilation. Patients are normally managed with pharmaceutical therapy, supplemental oxygen, or both.
Respiratory insufficiency due to muscle weakness
MedGen UID:
812797
Concept ID:
C3806467
Finding
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.
Abnormality of metabolism/homeostasis
MedGen UID:
867398
Concept ID:
C4021768
Finding
Weak cry
MedGen UID:
65892
Concept ID:
C0234860
Finding
Tongue fasciculations
MedGen UID:
65987
Concept ID:
C0239548
Finding
Fasciculations or fibrillation affecting the tongue muscle.
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.
Decreased fetal movement
MedGen UID:
68618
Concept ID:
C0235659
Finding
An abnormal reduction in quantity or strength of fetal movements.
Ptosis
MedGen UID:
2287
Concept ID:
C0005745
Disease or Syndrome
The upper eyelid margin is positioned 3 mm or more lower than usual and covers the superior portion of the iris (objective); or, the upper lid margin obscures at least part of the pupil (subjective).

Term Hierarchy

CClinical test,  RResearch test,  OOMIM,  GGeneReviews,  VClinVar  
  • CROGVInfantile-onset X-linked spinal muscular atrophy
Follow this link to review classifications for Infantile-onset X-linked spinal muscular atrophy in Orphanet.

Recent clinical studies

Diagnosis

Dlamini N, Josifova DJ, Paine SM, Wraige E, Pitt M, Murphy AJ, King A, Buk S, Smith F, Abbs S, Sewry C, Jacques TS, Jungbluth H
Neuromuscul Disord 2013 May;23(5):391-8. Epub 2013 Mar 18 doi: 10.1016/j.nmd.2013.02.001. PMID: 23518311

Prognosis

Dlamini N, Josifova DJ, Paine SM, Wraige E, Pitt M, Murphy AJ, King A, Buk S, Smith F, Abbs S, Sewry C, Jacques TS, Jungbluth H
Neuromuscul Disord 2013 May;23(5):391-8. Epub 2013 Mar 18 doi: 10.1016/j.nmd.2013.02.001. PMID: 23518311

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