Disease information

What is SMARD1?

SMARD1 is a rare genetic disease that affects the nerves controlling movement and breathing.

This page is a summary of disease information — not medical advice, and not our family’s personal account. It is written from the published medical sources listed at the end. Please discuss anything concerning your own child with your healthcare team.

SMARD1 at a glance

Cause
Changes in the IGHMBP2 gene
Inheritance
Both parents carry one changed copy; a child is affected only by inheriting both
Mainly affects
Motor neurons, skeletal muscle and respiratory function
Most serious complication
Respiratory failure from diaphragm weakness or paralysis
Care today
Supportive, multidisciplinary care

What is SMARD1?

SMARD1 stands for Spinal Muscular Atrophy with Respiratory Distress Type 1. It is a rare, inherited neuromuscular disease caused by changes in the IGHMBP2 gene.

In children with SMARD1, the motor neurons in the spinal cord — the nerve cells that carry the instruction to move from the spinal cord out to the muscles — are progressively damaged. The muscles stop receiving strong enough signals, and they weaken and waste over time.

Most importantly, the disease can weaken or paralyse the diaphragm — the main muscle we use to breathe. For many children this means respiratory failure begins in infancy, and long-term ventilatory support becomes necessary.

The disease is extremely rare and its true prevalence is still unknown. More than 60 cases have been reported in the scientific literature over the years, while fewer than 60 people are living with SMARD1 worldwide today. Because it is so rare, many clinicians will never see a single case in their career.

SMARD1 goes by several other names in the literature and in genetic reports, including autosomal recessive distal spinal muscular atrophy 1 (DSMA1), distal hereditary motor neuronopathy type VI (DHMN6), diaphragmatic spinal muscular atrophy, and severe infantile axonal neuropathy with respiratory failure (SIANRF). If your report uses one of these names, it refers to the same condition.

What happens in the body?

From gene to breathing, the chain of events can be followed one step at a time:

  1. 1

    IGHMBP2 gene variants

    The child inherits a changed copy of the IGHMBP2 gene from each parent.

  2. 2

    Reduced protein function

    The body makes little or no functional IGHMBP2 protein.

  3. 3

    Motor neuron degeneration

    Motor neurons in the spinal cord become damaged and gradually die.

  4. 4

    Signals to muscles are lost

    The nerve signals that control muscle movement are disrupted.

  5. 5

    Progressive muscle weakness

    Muscles receive weaker signals and become weaker over time.

From this point, the effects run along two paths:

Affects the body

Limb and body muscles

  • Progressive muscle weakness
  • Muscle wasting (atrophy)
  • Weakness often begins in the feet and distal lower limbs
  • Difficulty sitting, standing, walking and moving
  • Joint contractures and skeletal complications

Result: progressive weakness and loss of mobility

Affects breathing

Diaphragm (main breathing muscle)

  • Motor neurons controlling the diaphragm are severely affected
  • The diaphragm becomes weak or paralysed
  • Breathing becomes difficult or impossible

Result: respiratory failure → non-invasive or invasive ventilatory support may be required

One caveat: exactly why a shortage of IGHMBP2 protein damages motor neurons in particular is still not fully understood. The chain above reflects current mainstream understanding rather than a fully settled mechanism — which is part of why research continues.

What are the symptoms?

The features below are commonly reported. One important caveat: there is considerable variation between children with SMARD1 — age of onset, rate of progression and severity all differ, and not every child develops every symptom.

  • Difficult or noisy breathing on inhalation
  • Diaphragm weakness or paralysis leading to respiratory failure (often the first problem noticed)
  • Recurrent pneumonia
  • Limb muscle weakness and wasting, usually beginning distally in the hands and feet before spreading
  • Feeding and swallowing difficulty; poor weight gain
  • Weak cry
  • Loss of deep tendon reflexes, typically after the first year of life
  • Joint contractures and skeletal problems such as spinal curvature
  • Autonomic features such as excessive sweating, irregular heartbeat, and loss of bladder or bowel control
  • Reduced sensitivity to pain

Symptoms most often appear between a few weeks and six months of age, when sudden respiratory failure from diaphragm paralysis frequently occurs. Some children are first admitted for unexplained respiratory distress, and the underlying cause is only identified afterwards. One further point worth knowing: although the muscle weakness is progressive, it has been observed to stabilise in most children within about two years.

How is SMARD1 different from SMA?

This section matters. Because the name contains “SMA”, many people — including some healthcare professionals — assume that the approved SMA treatments will work for SMARD1. They will not. These are two different diseases.

SMARD1Typical SMA (5q SMA)
Gene involved IGHMBP2 SMN1
Where weakness starts Usually distal (feet, lower limbs) Usually proximal (muscles closer to the trunk)
Diaphragm Severely affected early; often the first problem Relatively spared early; intercostal muscles affected first
Approved medicines No approved treatment targeting the underlying cause Spinraza, Zolgensma, Evrysdi and others are approved

The critical difference is the last row: Spinraza (nusinersen), Zolgensma and Evrysdi (risdiplam) all act on the SMN protein, whereas SMARD1 is caused by a problem in IGHMBP2. These medicines are not treatment options for SMARD1.

How is SMARD1 inherited?

SMARD1 is inherited in an autosomal recessive pattern. That means a child must inherit a changed copy of the gene from each parent in order to be affected.

Both parents are usually carriers — each has one changed copy and one working copy. Because the working copy is enough, carriers are completely healthy and have no symptoms, and most have no idea until a child is diagnosed.

When both parents are carriers, each pregnancy has:

  • 25% Affected

    Inherits two changed copies

  • 50% Carrier

    Inherits one; healthy, no symptoms

  • 25% Unaffected non-carrier

    Inherits two working copies

Note the words “each pregnancy”: these odds do not change based on previous children. Every pregnancy carries the same independent 25% chance. If a family already has an affected child, genetic counselling can help with decisions about future pregnancies.

Is there a treatment?

Care today

There is currently no approved treatment that targets the underlying cause of SMARD1. Care today is supportive — aimed at maintaining a child’s function and quality of life as far as possible, and usually delivered by several specialties working together:

  • Respiratory support: non-invasive or invasive ventilation, and secretion clearance
  • Nutrition: feeding tubes, nutritional assessment and weight management
  • Rehabilitation and positioning: physiotherapy and occupational therapy to slow contractures
  • Orthopaedic follow-up: management of scoliosis and joint deformity
  • Other: pain management, autonomic symptom management, and psychological support for the family

Research

Treatments targeting the cause of SMARD1 are being researched, including gene therapy approaches. Most of the published work is at a preclinical stage; results in animal models have been considered encouraging, but more work is needed before a treatment is available for people.

This is the section that changes fastest. If you are looking for treatment options for your child, please confirm the current position with your healthcare team, and consider searching clinical trial registries.

International SMARD1 Patient Registry

There is an international patient registry dedicated to SMARD1. Registries exist to gather the very small number of cases scattered around the world into one place — the more cases are recorded, the better the chance that research can move forward.

Go to the SMARD1 Patient Registry

Sources

This page is compiled from the following published medical sources:

Last reviewed: August 2026

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