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infantile-onset X-linked spinal muscular atrophy (SMAX2) - Clinical Profile, Treatments & Trials | Kisho | Kisho

Features include always present findings: Elevated creatine kinase (muscle enzyme) (elevated circulating creatine kinase concentration), Low muscle tone (hypotonia), Tongue fasciculations, and Myopathic facies and others. 27 total HPO annotations.

Organ System	Phenotype Count	Example Features
Muscles	11	Flexion contracture, Myopathy, Low muscle tone (hypotonia)
Bones and joints	2	Sideways curvature of the spine (scoliosis), Multiple joint contractures
Lungs and breathing	2	Difficulty breathing (respiratory insufficiency), Difficulty breathing due to muscle weakness (respiratory insufficiency due to muscle weakness)
Head and neck	1	Facial palsy
Lab test results	1	Elevated creatine kinase (muscle enzyme) (elevated circulating creatine kinase concentration)
Brain and nerves	1	Tongue fasciculations
Metabolism	1	Abnormality of metabolism/homeostasis
Eyes	1	Ptosis
Pregnancy and birth	1	Decreased fetal movement

GeneReviews

Clinical Guidance

Males

X-linked infantile spinal muscular atrophy (XL-SMA) is characterized by severe hypotonia and areflexia with loss of anterior horn cells in the spinal cord (i.e., lower motor neurons). The disease course is similar to that of the most severe forms of classic autosomal recessive SMA (when supportive care only is given) caused by biallelic pathogenic variants in SMN1: SMA type 0 (SMA0) and SMA type I (SMA1) (see Spinal Muscular Atrophy). In SMA0, prenatal onset of weakness and poor intrauterine movement results in congenital contractures. In SMA1, motor skills regress before age six months in those receiving supportive care only; affected children who do not receive targeted therapies are never able to sit independently. Neuromuscular.

Source: GeneReviews — "Spinal Muscular Atrophy, X-Linked Infantile"

Diagnosis

Drawn from GeneReviews diagnostic guidelines, newborn screening panel status (RUSP), and ClinGen gene-disease validity classifications. Reflects current clinical evidence and consensus where available.

GeneReviews

Diagnostic Criteria

While suggestive diagnostic criteria were proposed by as part of inclusion criteria for a research study on this condition, no consensus clinical diagnostic criteria for X-linked infantile spinal muscular atrophy have been published.

Suggestive Findings

X-linked infantile spinal muscular atrophy should be suspected in an individual with the following clinical, imaging, electrophysiologic, supportive laboratory, and family history findings.

Clinical features

Congenital hypotonia and areflexia on physical examination
Congenital contractures and/or fractures
Digital contractures at birth. These usually remain throughout the individual's life.

Source: GeneReviews — "Spinal Muscular Atrophy, X-Linked Infantile"

GeneReviews

Differential Diagnosis

The differential diagnosis of X-linked infantile spinal muscular atrophy (XL-SMA) caused by mutation of UBA1 includes other disorders associated with spinal muscular atrophy and/or arthrogryposis . Table 2. Disorders with Spinal Muscular Atrophy and/or Contractures in the Differential Diagnosis of X-Linked Infantile Spinal Muscular Atrophy

MOI	Gene	Disorder1	Age of Onset	MultipleContractures2	Fractures	Hypotonia	MuscleWeakness

Genetic testing for UBA1 is available. Testing is considered confirmatory for diagnosis.

Treatment

Compiled from FDA-approved drug records, orphan drug designations, and FDA Adverse Event Reporting System (FAERS) safety data. GeneReviews management guidance is included where available.

3 FDA-approved treatments are available for infantile-onset X-linked spinal muscular atrophy, including NUSINERSEN (SPINRAZA, approved 2016), onasemnogene abeparvovec-xioi (Zolgensma, approved 2019), and RISDIPLAM (EVRYSDI, approved 2020).

Approved Therapies

Brand Name	Generic Name	Mechanism	Approved	Market Status
EVRYSDI	RISDIPLAM	—	2020	Available
Zolgensma	onasemnogene abeparvovec-xioi	—	2019	Available
SPINRAZA	NUSINERSEN	—	2016	Available

GeneReviews

Management Guidelines

Evaluations Following Initial Diagnosis To establish the extent of disease and needs in an individual diagnosed with X-linked infantile spinal muscular atrophy (XL-SMA), the evaluations summarized (if not performed as part of the evaluation that led to the diagnosis) are recommended. Table 3. Recommended Evaluations Following Initial Diagnosis in Individuals with X-Linked Infantile Spinal Muscular Atrophy

System	Evaluation	Comment
Neurologic	Assessment of muscle tone strength (if possible)	To guide supportive management1 Nutrition/
Feeding	Gastroenterology, nutrition, feeding team eval2	To incl eval of aspiration risk, fatigue during feeding, GERD, nutritional status; Consider eval for gastrostomy tube placement in those w/dysphagia /or aspiration risk /or poor oral intake. Respiratory/

GeneReviews

Therapies Under Investigation

Search ClinicalTrials.gov in the US and EU Clinical Trials Register in Europe for information on clinical studies for a wide range of diseases and conditions. Note: There may not be clinical trials for this disorder.

Source: GeneReviews — "Spinal Muscular Atrophy, X-Linked Infantile"

Clinical Trials

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Latest News & Developments

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AI-curated news mentioning infantile-onset X-linked spinal muscular atrophy

Updated Sep 18, 2026

SIGNIFICANT

Biotech Business•

Funding & Deals

•2 days ago(Sep 18)

This week in charts: GSK’s China deals, the $300M IPO club and selling the news | BioPharma Dive

The latest installment in BioPharma Dive’s new visualization-focused series features a stock sell-off that confused Wall Street analysts and a closer look at an industry-leading partnership streak. The top drugmaker IPOs, by total proceeds, since Jan. 1. Scholar Rock hit a milestone a week ago. The 14-year-old biotechnology company last Friday won its first regulatory approval with the U.S. clearance of Isembyld, a first-of-its-kind “muscle-targeted” treatment for the rare disease spinal muscular atrophy. A drug prominently featured at the World Conference on Lung Cancer last weekend came to GSK via a 2023 partnership with Hansoh Pharma. Jefferies analyst Michael Leuchten recently referred to that drug as an “underappreciated, potentially major oncology asset.” · Licensing deals between GSK and China-based drugmakers since the start of 2025. It’s no secret now that biotech initial public offerings have rebounded in 2026. Today, we’re looking at a spurt of China licensing deals from GSK, Electra Therapeutics’ big IPO and how investors responded to Scholar Rock’s long-awaited drug approval. Over the last couple years, the pharmaceutical industry has rushed to scoop up drugs discovered in China. More than 100 deals have been struck, according to BioPharma Dive data, a trend that’s sparked concern among U.S. lawmakers as well as debate among biotech executives and investors. Electra Therapeutics’ stock offering Thursday night was the latest example. In pricing its IPO, Electra became the 11th drugmaker to raise at least $300 million in proceeds. That figure matches 2021’s total — a record year for biotech IPOs — and surpasses the previous four years combined.

TOP STORY

Score: 90

BioPharma Dive•

Pipeline & Approvals

•6 days ago(Sep 14)

Scholar Rock SMA drug approved by FDA

FDA approves Isembyld, the first muscle-targeted treatment for spinal muscular atrophy, which has shown promise in improving motor function in patients on standard therapies. Analysts project it as a potential blockbuster in the rare disease market.

TOP STORY

Score: 95

BioSpace•

Pipeline & Approvals

•6 days ago(Sep 14)

Scholar Rock secures first FDA approval for muscle-targeting rare disease drug

Scholar Rock’s spinal muscular atrophy drug, now to be called Isembyld, was originally rejected in September 2025, when the FDA cited compliance problems at a third-party manufacturer.

PubMed Rare Disease•

Science & Discovery

•12 days ago(Sep 7)

Frequency and Circumstances of Falls Events in People Living With Spinal and Bulbar Muscular Atrophy: A Cross-Sectional Survey.

A cross-sectional survey investigates the frequency and circumstances of falls in individuals with spinal and bulbar muscular atrophy. This research highlights the need for targeted interventions to reduce fall risks in this patient population.

PubMed Rare Disease•

Science & Discovery

•29 days ago(Aug 22)

Integrating LNA-qPCR and full-length SMN1 sequencing for precision SMA carrier screening: large-scale validation in 30,849 individuals.

A study validates the integration of LNA-qPCR and full-length SMN1 sequencing for precision carrier screening of spinal muscular atrophy (SMA) in 30,849 individuals. This advancement could enhance early detection and management of SMA.

View all news for infantile-onset X-linked spinal muscular atrophy

Kisho

infantile-onset X-linked spinal muscular atrophy

Overview

Clinical Presentation

Clinical Guidance

Males

Explore clinical features

Genetic Landscape

Clinical Guidance

Diagnosis

Diagnostic Criteria

Suggestive Findings

Differential Diagnosis

Treatment

Approved Therapies

Management Guidelines

Therapies Under Investigation

Clinical Trials

Prognosis

Surveillance Guidelines

Growth

Neurologic

Feeding

Respiratory1

Skeletal

Research Landscape

Recent Publications

Medical References

External Resources

OMIM

Orphanet

GARD

Questions for Your Care Team

Questions for Your Care Team

Latest News & Developments

This week in charts: GSK’s China deals, the $300M IPO club and selling the news | BioPharma Dive

Scholar Rock SMA drug approved by FDA

Scholar Rock secures first FDA approval for muscle-targeting rare disease drug

Frequency and Circumstances of Falls Events in People Living With Spinal and Bulbar Muscular Atrophy: A Cross-Sectional Survey.

Integrating LNA-qPCR and full-length SMN1 sequencing for precision SMA carrier screening: large-scale validation in 30,849 individuals.

infantile-onset X-linked spinal muscular atrophy

Overview

Clinical Presentation

Clinical Guidance

Males

Explore clinical features

Genetic Landscape

Clinical Guidance

Diagnosis

Diagnostic Criteria

Suggestive Findings

Differential Diagnosis

Treatment

Approved Therapies

Management Guidelines

Therapies Under Investigation

Clinical Trials

Prognosis

Surveillance Guidelines

Growth

Neurologic

Feeding

Respiratory1

Skeletal

Research Landscape

Recent Publications

Medical References

External Resources

OMIM

Orphanet

GARD

Related Diseases

Questions for Your Care Team

Questions for Your Care Team

Latest News & Developments

This week in charts: GSK’s China deals, the $300M IPO club and selling the news | BioPharma Dive

Scholar Rock SMA drug approved by FDA

Scholar Rock secures first FDA approval for muscle-targeting rare disease drug

Frequency and Circumstances of Falls Events in People Living With Spinal and Bulbar Muscular Atrophy: A Cross-Sectional Survey.

Integrating LNA-qPCR and full-length SMN1 sequencing for precision SMA carrier screening: large-scale validation in 30,849 individuals.