Symptoms, Seizures, and Brain Development

Because SLC35A2-CDG primarily affects the brain, the symptoms are mostly neurological. While the diagnosis can be frightening, it is important to know that the severity of these symptoms can vary significantly from one child to another ^[1][2].

Understanding the “Encephalopathy” Pattern

Many children with this condition present with what doctors call Developmental and Epileptic Encephalopathy (DEE). This means that developmental impairment arises from both the underlying genetic neurodevelopmental disorder and the disruptive electrical activity from seizures ^[3][4]. Developmental delay can occur before seizures begin, or persist despite seizure control.

The most common way this starts is through infantile spasms (also called West Syndrome). These are not typical “shaking” seizures; instead, they often look like sudden, brief clusters of head drops or the body “scrunching” forward ^[3]. When a child has these spasms, their EEG (a test that measures brain waves) often shows a chaotic, high-voltage pattern called hypsarrhythmia ^[4]. Suspected infantile spasms require urgent neurologic assessment even when individual events are brief. If left untreated, this chaotic brain activity can significantly slow down or even “pause” a child’s development.

Seizure Variability

While epilepsy is frequent in reported cohorts, the experience is not the same for everyone:

• Early Encephalopathy: Some infants start having spasms very early, often leading to more significant intellectual challenges ^[1].
• Focal Epilepsy: Other children may have seizures that come from one specific spot in the brain ^[1].
• Seizure-Free Cases: There are reported cases of children with SLC35A2-CDG who have never had a seizure at all, or who have only minor neurological symptoms ^[5][2].

Seizures in this condition can sometimes be drug-resistant, meaning they don’t respond well to standard medications. Some doctors have found success using hormonal treatments like ACTH, though the benefit may sometimes be temporary ^[4][6].

Developmental Milestones and Muscle Tone

Many children with SLC35A2-CDG experience some level of Global Developmental Delay (GDD), which affects physical movement, speech, and social interaction ^[3].

• Hypotonia: This is the medical term for low muscle tone. You might notice your child feels “floppy” or has difficulty holding their head up or sitting without support ^[3].
• Motor Skills: Many children face significant challenges with mobility. In some studies, many children remained “nonambulatory” (meaning they did not learn to walk on their own), while others developed spasticity (stiffness) in their legs ^[3][7].
• Vision: Some children have cortical visual impairment (CVI), where the eyes are healthy but the brain has trouble processing what it sees ^[7].

What the Brain MRI Shows

When doctors look at a brain MRI of a child with SLC35A2-CDG, they often see variable signs that can point to the diagnosis, though MRI alone cannot confirm or predict long-term outcomes:

• Delayed Myelination: Myelin is the protective coating around nerve fibers (like insulation on a wire). In this condition, the brain may be slow to develop this coating, which slows down the signals sent between brain cells ^[3].
• Thin Corpus Callosum: The corpus callosum is the bridge that allows the left and right sides of the brain to talk to each other. In many patients, this bridge is smaller or thinner than usual ^[3][8].
• Cerebral Atrophy: This refers to a slight shrinking or “thinning” of the brain tissue. While it is reported, it is not always progressive ^[3][7].
• White Matter Abnormalities: Doctors may see patchy “bright spots” in the white matter of the brain, which usually stay stable over time rather than getting worse ^[3].

Understanding these findings helps your care team tailor therapies—such as physical, occupational, and speech therapy—to your child’s specific needs.