infantile-onset X-linked spinal muscular atrophy
Findings
No curated finding names infantile-onset X-linked spinal muscular atrophy yet. Everything below is reference data from Mondo, HPO and GenCC, not evidence about what affects it.
Definition
A rare form of spinal muscular atrophy characterized by the neonatal onset of severe hypotonia, areflexia, profound weakness, multiple congenital contractures, facial dysmorphic features (myopathic face with open, tent-shaped mouth), cryptorchidism, and mild skeletal abnormalities (i.e. kyphosis, scoliosis), that is often preceded by polyhydramnios and reduced fetal movements in utero and followed by bone fractures shortly after birth. SMAX2 patients often have a limited life span, often succumbing to the disease within 2 years, as muscle weakness is progressive and chest muscle involvement eventually leads to ventilatory insufficiency and respiratory failure.
Definition from the Mondo Disease Ontology (MONDO:0010532), read 2026-09-29. CC BY 4.0.
- Inheritance
- X-linked recessive inheritance
- Onset and course
- Neonatal onset
HPO, annotations 2026-09-02
Features
41 features
What the disease is reported to present with, and how often among people who have it — never how often a feature means the disease. HPO, annotations 2026-09-02.
- Decreased compound muscle action potential amplitudeHPOHP:0033383
- 1 of 1 reported patient
- Elevated circulating creatine kinase activityHPOHP:0003236
- 1 of 1 reported patient
- Persistent head lagHPOHP:0032988
- 1 of 1 reported patient
- Weak cryHPOHP:0001612
- 1 of 1 reported patient
- Abnormal anterior horn cell morphologyHPOHP:0006802
- Very frequent (80% to 99% of cases)
- Abnormal muscle fiber morphology
Genes
1 gene
Germline variants in the gene encoding each protein, as classified by GenCC submitters, each in their own words. Limited, disputed and refuted submissions are listed too.
- UBA1HGNC:12469
- Strong · Genomics England PanelApp · X-linked · 2021
- Strong · Labcorp Genetics (formerly Invitae) · X-linked · 2021
- Strong · PanelApp Australia · X-linked · 2025
- Moderate · Ambry Genetics · X-linked · 2017
- Supportive · Orphanet · X-linked · 2021
Where it sits
Other names
6 names
Resolves to: infantile-onset X-linked spinal muscular atrophy
- Also called
- SMAX2spinal muscular atrophy with arthrogryposisspinal muscular atrophy, X-linked 2, infantile, X-linked recessivespinal muscular atrophy, X-linked type 2X-linked distal arthrogryposis multiplex congenitaX-linked spinal muscular atrophy type 2