Snijders Blok-Campeau Syndrome (SBCS) is a rare neurodevelopmental disorder impacting multiple body systems. It is classified as an autosomal dominant condition, meaning a change in a single copy of the responsible gene causes the syndrome. First described in 2018, SBCS is characterized by global developmental delays, intellectual disability, and a spectrum of speech and language impairments. The variable severity of its effects impacts a person’s development and quality of life.
The Role of the CHD3 Gene
The underlying cause of Snijders Blok-Campeau Syndrome (SBCS) is a pathogenic variant in the CHD3 gene, which stands for Chromodomain Helicase DNA-binding protein 3. This gene is located on chromosome 17 and provides instructions for creating a protein that is fundamental to gene regulation. The CHD3 protein is a component of a larger assembly known as the NuRD complex, which is an adenosine triphosphate (ATP)-dependent chromatin remodeling factor.
Chromatin is the tightly packed structure of DNA and proteins that forms chromosomes within the cell’s nucleus. The CHD3 protein helps remodel this chromatin structure, essentially deciding whether DNA is tightly packed or loosely packed. This “remodeling” process is how the cell controls which genes are turned “on” or “off” at specific times, a mechanism that is particularly important during early brain development.
In SBCS, the gene variants are almost always de novo, meaning the genetic change occurs spontaneously and is not inherited. These variants disrupt the CHD3 protein’s function, altering the chromatin remodeling process. This leads to the misregulation of genes crucial for development. This disruption in gene expression during brain formation ultimately causes the syndrome’s neurodevelopmental and physical characteristics.
Recognizing the Clinical Features
The clinical presentation of Snijders Blok-Campeau Syndrome is highly variable but centers on a core set of neurodevelopmental and physical characteristics. Global developmental delay and impaired intellectual development are nearly universal features of the syndrome, with intellectual disability ranging from mild to severe. Speech and language difficulties are prominent, including a high frequency of expressive language deficits like dysarthria and speech apraxia.
Dysarthria involves difficulties with the muscle control needed for clear speech, while speech apraxia is a problem with planning muscle movements for speech. Low muscle tone (hypotonia) is common, contributing to delays in motor milestones like walking. Behavioral challenges are frequently reported, often including traits consistent with autism spectrum disorder (ASD) or attention deficit hyperactivity disorder (ADHD).
Physical and craniofacial features are often distinctive in SBCS, though not all individuals exhibit every sign. Macrocephaly, or an unusually large head size, is a common feature, along with a prominent forehead, sometimes referred to as frontal bossing. Other facial characteristics can include widely spaced eyes, known as hypertelorism, and a broad nasal bridge or pointed chin.
Associated medical issues can affect other organ systems. Vision problems are common, including strabismus (misaligned eyes) or farsightedness (hyperopia). Less common features include structural heart problems, such as an atrial septal defect, or skeletal anomalies like scoliosis. Approximately half of affected individuals may also have brain abnormalities visible on imaging, such as enlarged spaces containing cerebrospinal fluid.
Establishing a Diagnosis
The process of establishing a diagnosis for Snijders Blok-Campeau Syndrome begins with a high degree of clinical suspicion based on the patient’s pattern of symptoms. A clinician, often a developmental pediatrician or geneticist, will observe the combination of global developmental delay, severe speech impairment, and characteristic physical features. However, a definitive diagnosis cannot be made based on clinical findings alone due to the variability and overlap with other neurodevelopmental disorders.
Genetic testing is necessary to confirm the condition by identifying the pathogenic variant in the CHD3 gene. The most common method for this confirmation is Whole Exome Sequencing (WES), which analyzes the protein-coding regions of an individual’s entire genome. Targeted gene panels that include the CHD3 gene may also be used if there is a strong initial suspicion.
Confirmation of a de novo variant in CHD3 provides a clear molecular explanation for the symptoms observed. This genetic confirmation allows for a more accurate prognosis and connects families with relevant resources and support groups. The diagnosis provides a specific understanding of the underlying cause, which is crucial for therapeutic planning. Genetic counseling is offered to discuss the low risk of recurrence in future pregnancies, given the de novo nature of the mutation.
Multidisciplinary Care Strategies
Since there is currently no cure for Snijders Blok-Campeau Syndrome, the long-term management focuses entirely on supportive care and maximizing the individual’s developmental potential. This requires a coordinated approach involving a multidisciplinary team of specialists to address the wide range of symptoms. Therapeutic interventions are often initiated early to capitalize on the brain’s plasticity during childhood.
Speech and language therapy is a primary treatment, addressing communication challenges like apraxia and dysarthria. This therapy focuses on articulation, motor planning for speech, or alternative communication methods. Physical and occupational therapy are essential for addressing hypotonia and motor delays, improving strength, coordination, and fine motor skills for daily living.
Specialized educational support is also a fundamental part of the care strategy, including the implementation of Individualized Education Plans (IEPs) in school settings. These plans ensure that learning environments and instruction are tailored to the individual’s specific intellectual and behavioral needs. Behavioral support strategies are often necessary to manage symptoms related to ASD or ADHD, focusing on communication skills and adaptive behaviors.
Medical oversight involves regular monitoring by a neurologist for conditions like seizures. Developmental pediatricians and specialists, such as ophthalmologists and cardiologists, manage associated issues like vision problems and congenital heart defects. This comprehensive support is provided throughout the individual’s life.