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X-linked spinal muscular atrophy 2
Description
X-linked spinal muscular atrophy type 2 (SMAX2) is a rare and severe form of spinal muscular atrophy that affects only boys. It is characterized by:
- Neonatal onset: Symptoms typically appear in the first few days or weeks of life.
- Severe hypotonia: Affected individuals have significantly reduced muscle tone, making it difficult to move or maintain posture.
- Areflexia: Absence of reflexes, which can make it challenging to assess muscle strength and tone.
- Multiple congenital contractures: Joints are stiff from birth, leading to impaired movement and mobility.
- Facial dysmorphic features: Individuals with SMAX2 often have a distinctive facial appearance, including a myopathic face with an open, tent-shaped mouth.
- Cryptorchidism: Undescended testes are common in affected individuals.
- Mild skeletal abnormalities: Some people with SMAX2 may experience mild curvature of the spine (kyphosis) or scoliosis.
This condition is inherited in an X-linked recessive pattern, meaning that only boys can be affected. The gene associated with this disorder, UBA1, is located on the X chromosome at Xp11.3 and contains 27 exons.
It's essential to note that SMAX2 is a rare and severe form of spinal muscular atrophy, and life expectancy is significantly shortened due to progressive ventilatory insufficiency [7][12].
Additional Characteristics
- Cryptorchidism
- Neonatal onset
- Severe hypotonia
- Facial dysmorphic features
- Areflexia
- Multiple congenital contractures
- Mild skeletal abnormalities
Signs and Symptoms
Symptoms of X-linked Spinal Muscular Atrophy Type 2
X-linked spinal muscular atrophy type 2 is a genetic disorder that affects only boys, characterized by severe muscle weakness and absent reflexes. The symptoms of this condition can vary in severity, but typically include:
- Congenital hypotonia: Weakness or floppiness of the muscles from birth
- Areflexia: Absent or decreased reflexes
- Degeneration and loss of anterior horn cells: Lower motor neurons in the spinal cord and brain stem are affected, leading to progressive muscle weakness and wasting
- Congenital contractures and/or fractures: Some individuals may be born with contractures (stiffness) or fractures due to weakened muscles
- Normal intellect: Intelligence is typically unaffected
As the condition progresses, symptoms can worsen, leading to:
- Progressive muscle weakness: Muscle strength decreases over time, affecting various bodily functions such as swallowing and walking
- Muscle wasting (atrophy): Muscles shrink or waste away due to lack of use
- Low muscle tone (hypotonia): Weakness or floppiness of the muscles
In individuals with type 2 X-linked spinal muscular atrophy, symptoms typically begin within the first few months of life. The condition is inherited in an X-linked recessive pattern, meaning that only males are affected, as they have one X and one Y chromosome.
References:
- [1] Congenital hypotonia and areflexia are characteristic features of X-linked spinal muscular atrophy type 2.
- [2-3] Degeneration and loss of anterior horn cells lead to progressive muscle weakness and wasting.
- [4-5] Congenital contractures and/or fractures may be present in some individuals.
- [6] The condition is inherited in an X-linked recessive pattern, affecting only males.
Additional Symptoms
- Congenital hypotonia
- Low muscle tone (hypotonia)
- Progressive muscle weakness
- Muscle wasting (atrophy)
- Degeneration and loss of anterior horn cells
- or fractures
- Normal intellect
- areflexia
Diagnostic Tests
Diagnostic Tests for X-linked Spinal Muscular Atrophy 2 (XL-SMA2)
X-linked spinal muscular atrophy type 2 (SMAX2, XL-SMA2) is a rare neurological disorder characterized by muscle weakness, hypotonia, areflexia, myopathic face, tongue fibrillations, contractures, bone fractures, and cryptorchidism. Diagnostic testing for XL-SMA2 involves a combination of clinical evaluation, genetic testing, and other diagnostic procedures.
Clinical Evaluation
A thorough physical examination is essential to determine the presence of symptoms such as muscle weakness, hypotonia, areflexia, myopathic face, tongue fibrillations, contractures, bone fractures, and cryptorchidism. A doctor may also perform a neurological examination to assess muscle strength, tone, and reflexes.
Genetic Testing
Molecular genetic testing is the standard tool for diagnosis of XL-SMA2. This test can detect mutations in the UBA1 gene, which causes the disease. Genetic testing involves a simple blood test that can identify the presence of the mutation associated with SMA. The test can also determine how many SMN2 genes a person has and roughly predict the course of SMA that is likely to result.
Other Diagnostic Procedures
In addition to genetic testing, other diagnostic procedures may be performed to rule out other conditions that may present similar symptoms. These tests include electromyography (EMG), nerve conduction study (NCS), or muscle biopsy. Blood tests may also be conducted to help determine the presence of SMA.
Carrier Testing
Carrier testing is available through a simple blood test, which can detect the most common mutation associated with SMA and will detect carriers of XL-SMA2.
References:
- [7] X-linked infantile spinal muscular atrophy is a condition that affects only boys and is characterized by severe muscle weakness and absent reflexes.
- [15] Genetic testing – Molecular genetic testing can confirm the diagnosis in infants and children with suspected SMA by detection of homozygous deletions of exons 7 of the SMN1 gene.
- [12] Spinal muscular atrophy, X-linked 2 (SMAX2) is a rare type of spinal muscular atrophy characterized by muscle weakness, hypotonia, areflexia, myopathic face, tongue fibrillations, contractures, bone fractures, and cryptorchidism.
Additional Diagnostic Tests
- Blood Tests
- Nerve Conduction Study (NCS)
- Genetic Testing
- Muscle Biopsy
- Electromyography (EMG)
Treatment
Current Drug Treatments for X-linked Spinal Muscular Atrophy Type 2
X-linked spinal muscular atrophy type 2 is a rare and severe form of spinal muscular atrophy (SMA). While there are no specific drug treatments approved for this condition, the general treatment approach for SMA can be applied. However, it's essential to note that the effectiveness of these treatments may vary depending on the individual case.
- Mechanical ventilation: This is often necessary to support breathing in individuals with severe SMA, including X-linked spinal muscular atrophy type 2.
- Feeding tube: A feeding tube may be required to ensure adequate nutrition and hydration.
- Gastrostomy: In some cases, a gastrostomy (a surgical procedure that creates an opening between the stomach and the abdominal wall) may be necessary for feeding.
- Orthopedic interventions: These may include physical therapy, bracing, or surgery to manage muscle weakness and prevent deformities.
It's worth noting that there are no known efficacious drug treatments specifically approved for X-linked spinal muscular atrophy type 2. However, researchers continue to explore new therapeutic options, including gene therapies and small molecule treatments.
References:
- [6] December 27, 2023 - Overall treatment aims at alleviating the symptoms and may include mechanical ventilation, feeding tube, gastrostomy, and orthopedic interventions.
- [7] Children with SMA type II do not develop the ability to walk without assistance and have a poor prognosis. There are no known efficacious drug treatments that influence the disease course of SMA.
Please note that these references are based on general information about spinal muscular atrophy and may not specifically address X-linked spinal muscular atrophy type 2.
Recommended Medications
- Mechanical ventilation
- Orthopedic interventions
- Feeding tube
- Gastrostomy
💊 Drug information is sourced from ChEBI (Chemical Entities of Biological Interest) database. Always consult with a healthcare professional before starting any medication. Click on any medication name for detailed information.
Differential Diagnosis
The differential diagnosis for X-linked infantile spinal muscular atrophy (XL-SMA) includes several conditions that can present with similar symptoms. Some of these conditions are:
- Congenital muscular dystrophies: These are a group of disorders characterized by muscle weakness and degeneration, often present at birth [7].
- Congenital myopathies: This is a rare condition where there is abnormal development of the muscles in the womb, leading to muscle weakness and wasting [8].
- Congenital myasthenic syndromes: These are conditions that affect the nerve-muscle connection, causing muscle weakness and fatigue [7].
- Neuromuscular junction disease: This refers to a group of disorders that affect the communication between nerves and muscles, leading to muscle weakness and wasting [8].
It's worth noting that X-linked infantile spinal muscular atrophy is a specific condition caused by mutations in the UBA1 gene on the X chromosome. A diagnosis can usually be made with the presence of congenital fractures and/or contractures, as well as other characteristic features such as hypotonia, weakness, and absent reflexes (areflexia) [2].
References: [7] - Congenital muscular dystrophies, congenital myopathies, congenital myasthenic synd
Additional Differential Diagnoses
- hereditary spastic paraplegia 38
- Congenital myopathies
- Congenital muscular dystrophies
- Congenital myasthenic syndromes
- neuromuscular junction disease
Additional Information
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It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified healthcare provider with questions about your medical condition.