Introduction 

Inherited peripheral neuropathies, or IPNs, encompass a charmingly diverse group of conditions affecting the peripheral nervous system. These illnesses come with a variety of genetic causes, clinical presentations, and age of onset. They’re among the most common hereditary nervous system disorders, though their symptoms can differ quite a lot. Charcot–Marie–Tooth disease type 1 (CMT1) and Dejerine–Sottas Syndrome (DSS) are two key examples within this group.¹

Both of these are mainly demyelinating neuropathies, which means they affect the myelin sheath around nerves. This can slow down nerve signals and cause muscle weakness or sensory issues. Although they share similar underlying mechanisms, these two conditions often appear and progress in different ways. CMT1 often begins in late childhood or adolescence, with gradually worsening weakness and sensory issues in the hands and feet, usually allowing people to walk well into adulthood.² In contrast, DSS typically shows up in infancy or early childhood, causing more severe weakness, delayed motor milestones, and a faster decline into significant disability.

The purpose of this article is to critically distinguish DSS from CMT1, examining their historical classification, clinical manifestations, genetic underpinnings, neuropathological features, and diagnostic approaches.

Historical Background and Classification

Dejerine–Sottas Syndrome (DSS) was first described in 1893 by French neurologists Joseph Jules Dejerine and Jules Sottas, who reported children with profound muscle weakness, delayed motor development, and striking nerve hypertrophy on pathological examination.³ At the time, the condition was termed “hypertrophic interstitial neuritis of infancy” to reflect both its early onset and its distinctive pathological features. In parallel, Charcot–Marie–Tooth disease (CMT) had already been characterised in 1886 by Jean-Martin Charcot, Pierre Marie, and Howard Henry Tooth as a hereditary motor and sensory neuropathy with progressive distal weakness and sensory loss.

Over the 20th century, advances in electrophysiology led to the distinction between CMT type 1, characterised by primary demyelination and slowed nerve conduction, and CMT type 2, marked by axonal degeneration. With the advent of molecular genetics in the 1990s, mutations in genes such as PMP22 and MPZ were identified in both CMT1 and DSS, blurring the historical separation between these syndromes.⁴ This overlap has fuelled debate as to whether DSS should be regarded as a distinct nosological entity or as a severe, early-onset variant within the demyelinating CMT1 spectrum.

Charcot–Marie–Tooth Disease Type 1 (CMT1)

CMT1 is the most prevalent demyelinating hereditary neuropathy, typically manifesting clinically in late childhood or adolescence. The first indicators are usually trouble running, falling a lot, or being clumsy because the muscles in the feet and legs are weak. Patients usually get foot abnormalities such as pes cavus and hammertoes as the disease gets worse.⁵ This is because the muscles have been out of balance for a long time. Foot drop is a common problem that makes it hard to walk.

The weakness in CMT1 usually starts in the lower limbs and moves up to the upper limbs. As time goes on, muscle atrophy becomes more noticeable, especially in the calves, which gives rise to the "stork leg" look. Patients may notice numbness, tingling, or a decreased sense of vibration in their hands and feet, but sensory involvement is usually less noticeable than motor impairment. Tendon reflexes are often diminished or absent, indicative of demyelinating neuropathy.

The course of CMT1 is slowly progressive. Importantly, despite the visible muscle wasting and foot deformities, many individuals with CMT1 maintain good functional ability and remain ambulant well into adulthood, often with the help of orthoses or supportive footwear. Disability is usually classified as mild to moderate, and life expectancy is not affected.⁶

The variability of expression is wide, even within families, but overall, CMT1 follows a predictable trajectory of childhood onset, gradual progression, distal predominance, and long-term preservation of mobility. These hallmarks distinguish it from more severe neuropathies such as Dejerine–Sottas Syndrome, which present earlier, progress more rapidly, and lead to significant disability at a much younger age.

Dejerine–Sottas Syndrome (DSS)

When compared to CMT1, Dejerine–Sottas Syndrome (DSS) shows up much earlier and is severity is higher. Usually, it starts when the person is a baby or very young child, usually in their first two years of life. Some parents may notice that their child has extreme hypotonia, is behind on motor milestones like sitting or walking, and is generally "floppy."

When someone has DSS, their weakness gets a lot worse over time. It affects both the proximal and distal muscles and makes it hard for them to move quickly. Lack of reflexes and more noticeable sense loss than in CMT1, often affecting both large and small fibre types. A big sign is ataxia, which shows both sensory participation and motor weakness. Deformities of the bones and joints show up early and are common. These include serious pes cavus, hammertoes, kyphoscoliosis, and joint contractures.⁷

Neuropathology and Electrophysiology

Electrophysiological testing is a key part of telling demyelinating neuropathies apart. Motor nerve conduction velocities (NCVs) are usually slower in people with CMT1, but they stay above 20 m/s. In most cases, they are less than 38 m/s. The slowing is usually the same on all nerves, which means that there is a problem with the myelin all over the nerves instead of just one area that is damaged. Compound muscle action potentials (CMAPs) may have less intensity, but they can usually be recorded.

Conduction speeds are slowed down a lot more in Dejerine–Sottas Syndrome (DSS). NCVs usually go below 10–15 m/s, and reactions may not be able to be recorded because the demyelination is so deep. One of the most important electrophysiological differences between DSS and the weaker CMT1 phenotype is this level of slowing.⁸

From a pathological point of view, nerve biopsies from both diseases show onion bulb formations, which are made up of layers of Schwann cells and collagen around axons. These happen after many rounds of demyelination and remyelination. In DSS, on the other hand, the onion bulbs are bigger, there are more of them, and the peripheral nerves have a lot of extra growth. Segmental demyelination and remyelination are worse, and the myelin sheaths are often very different from what they should be. Because of this, the general histological picture in DSS is much more dramatic than in CMT1, which is in line with the fact that the disease is more severe.

Diagnostic Approaches

It is important to carefully combine clinical, electrophysiological, pathological, and genetic information in order to provide an accurate diagnosis of inherited neuropathies. The first stage is a thorough clinical evaluation that looks at when the symptoms started, how bad they are, and how quickly they are getting worse. Dejerine–Sottas Syndrome (DSS) is likely if there is a history of delayed motor milestones, early hypotonia, and rapid functional deterioration. Charcot–Marie–Tooth disease type 1 (CMT1), on the other hand, is more likely if the symptoms start later and worsen more slowly.

Electrophysiological testing provides crucial objective data. In CMT1, nerve conduction velocities are uniformly slowed to less than 38 m/s, while in DSS, they are dramatically reduced, often below 10–15 m/s, or entirely unrecordable. These differences remain one of the most reliable ways to distinguish between the two.

Historically, nerve biopsy was frequently employed to demonstrate onion bulb formation and assess myelin abnormalities. While this can still highlight the more pronounced hypertrophy in DSS, the procedure is now less common due to its invasive nature and the availability of molecular diagnostics.

Finally, MRI or ultrasound can reveal nerve hypertrophy, which is often more pronounced in DSS. Establishing the correct diagnosis is critical for patient management, prognosis, family planning, and potential inclusion in emerging gene-targeted therapies.

Management and Prognosis

Currently, there is no cure for either Dejerine–Sottas syndrome (DSS) or Charcot–Marie–Tooth disease type 1 (CMT1). Management is therefore supportive, aiming to maximise function and quality of life. Physiotherapy helps maintain muscle strength and flexibility, while orthotic devices such as ankle–foot orthoses support mobility and prevent falls. In cases of severe deformities, orthopaedic surgery may be required to correct pes cavus, hammertoes, or scoliosis. Pain management and occupational therapy are also valuable in maintaining daily independence.

Genetic counselling is a crucial component of care. Families benefit from understanding inheritance patterns, recurrence risks, and implications for family planning.⁹

Prognosis differs markedly between the two disorders. CMT1 generally carries a favourable outlook, with a normal lifespan and only mild to moderate disability; most patients remain ambulant throughout life. In contrast, DSS has a poorer prognosis, with early and severe disability, frequent wheelchair dependency in childhood, and variable life expectancy depending on the severity of complications.

Summary

There are two inherited neuropathies, Dejerine–Sottas Syndrome (DSS) and Charcot–Marie–Tooth disease type 1 (CMT1). Both of them affect the myelin sheath and have similar genetic and clinical traits. CMT1 starts later, has less impairment, and keeps most of its movement, while DSS starts earlier, is worse, and has much slower conduction speeds. People used to think that DSS and CMT were two separate diseases.

However, more and more evidence shows that DSS is actually a serious form of demyelinating CMT that starts early. For patients and their families, getting a precise genetic diagnosis is still very important because it helps them understand their outlook, get genetic counselling, and be a part of future clinical studies. As research goes forward, the main goal is to describe both neuropathies on a scale and make gene-targeted medicines that might be able to change how the illnesses progress.