Can ARSACS Start in Adulthood? Late-Onset Symptoms

Yes, it is entirely possible to be diagnosed with ARSACS as an adult without having had noticeable symptoms as a child. While “classic” ARSACS is identified by delayed walking in toddlers ^[1], “atypical” or late-onset ARSACS is a well-documented variation of the condition ^[2]. If you spent years experiencing intense confusion or misdiagnosis before finally being identified, your experience is unfortunately very common for adult-onset patients.

Why Do Symptoms Start Later in Life?

ARSACS is caused by variations (mutations) in the SACS gene, which provides instructions for making a protein called sacsin. Sacsin is crucial for the health and function of your nerve cells.

In classic early-onset ARSACS, genetic mutations lead to an almost total loss of the sacsin protein from birth ^[3][4]. However, in atypical late-onset cases, the severity of the specific mutation (its pathogenicity) can be lower ^[5]. Researchers have found that certain specific SACS gene variants—such as specific missense mutations (a single-letter typo in your DNA code)—may allow for some partial sacsin protein function or stability ^[5][2].

This small amount of working protein may be enough to protect your nervous system throughout childhood. It is only when the cumulative stress on your nerve cells reaches a certain threshold over decades that symptoms finally begin to manifest ^[2].

How Adult-Onset ARSACS Differs from the Classic Form

The classic triad of ARSACS symptoms in children involves ataxia (loss of balance and coordination), spasticity (stiff, rigid muscles), and peripheral neuropathy (nerve damage in the arms and legs).

If you developed symptoms as an adult, your clinical presentation might look quite different from this classic triad:

• Lack of Spasticity: Many late-onset patients present with ataxia and polyneuropathy but do not experience the muscle spasticity that defines childhood cases ^[6][7].
• Gait Instability and Weakness: Symptoms often begin as progressive unsteadiness when walking, or subtle weakness in the lower legs, rather than the severe early motor delays seen in classic ARSACS ^[2][7].
• Missing MRI Clues: In early-onset ARSACS, brain MRIs frequently show characteristic “stripes” in the pons (a part of the brainstem). In adult-onset cases, these classic brain-imaging manifestations may be completely absent, making the condition incredibly difficult for general neurologists to identify ^[6][7].

A Highly Specific Clue: The Eyes

Even when physical symptoms and brain MRIs are atypical, most people with ARSACS—regardless of their age of onset—share one highly specific feature: a thickening of the retinal nerve fiber layer (RNFL) ^[8][9]. This is an abnormality in the back of the eye that does not typically affect your vision but can be easily detected with a non-invasive eye scan called Optical Coherence Tomography (OCT). If your doctors were puzzled by your physical symptoms, an eye scan or genetic testing was likely the key to confirming your diagnosis ^[8][4].

Looking Forward

Being diagnosed with a rare genetic condition as an adult can be overwhelming, but understanding that your late-onset form is biologically distinct can be reassuring. Because the disease manifests later in life, researchers suggest that late-onset ARSACS may progress at a different rate and have an extended “therapeutic window” ^[2]. This means you may have more time to intervene with targeted physical therapy, symptom management (such as orthotic devices for gait instability or medications for neuropathy), and potential future treatments compared to those who develop the condition in infancy.