CHD3 Syndrome: Causes, Symptoms, and Diagnosis

CHD3 syndrome, also known as Snijders Blok-Campeau syndrome, is a rare genetic condition that influences brain and body development. It presents with a wide array of signs that can differ from person to person. This article provides an overview of the syndrome’s genetic foundations, its key characteristics, and how it is identified.

Understanding the CHD3 Gene and Its Role

Every cell contains genes, which act as instructions for building and operating the body. The CHD3 gene provides the code for making a protein that is active during the early stages of brain development. This protein plays a part in a process called chromatin remodeling, which helps manage which genes are turned on or off at specific times.

This regulation is important for ensuring that brain cells, or neurons, move to their correct locations as the brain forms. By controlling the activity of other genes, the CHD3 protein helps construct the brain’s complex architecture. A mutation, or change in the genetic code, of the CHD3 gene disrupts the normal function of this protein.

Most mutations in the CHD3 gene are de novo, meaning “new.” This signifies that the genetic change occurred spontaneously in either the sperm or egg cell before conception or very early in embryonic development. In most instances, the mutation is not passed down from a parent. This alteration is the direct cause of the developmental differences seen in the syndrome.

Key Characteristics and Symptoms

The effects of a CHD3 gene mutation impact cognitive and physical growth. Individuals often experience developmental delays, delaying milestones like sitting, standing, and walking. The degree of intellectual disability varies widely among those affected, with IQ scores ranging from just below the typical range to severe.

Speech and language are significantly affected. Many individuals are slow to develop these skills, with some speaking their first words after age two, while others may acquire only a few words or remain nonverbal. Difficulties can include oromotor dysfunction, which is poor coordination of the mouth and tongue, and issues producing the sound sequences needed to form words.

Distinctive physical characteristics are also associated with CHD3 syndrome. A common feature is macrocephaly, or an unusually large head size. Facial differences often include:

• Widely spaced eyes
• A broad or prominent forehead
• Sparse eyebrows
• Low-set ears
• A pointed chin

Other physical signs can include low muscle tone (hypotonia) and unusually flexible joints.

Process of Diagnosis

The journey to a diagnosis often begins when a healthcare provider observes a pattern of developmental delays and specific physical features. These initial observations are the first step in a process that requires more specialized investigation to confirm a suspected genetic cause.

A definitive diagnosis is made through genetic testing. Tests like whole exome sequencing or targeted sequencing of the CHD3 gene can identify the specific mutation responsible for the symptoms. This genetic confirmation is necessary to distinguish CHD3 syndrome from other neurodevelopmental conditions that may present with overlapping features.

The diagnostic process may also involve ruling out other potential causes for the observed symptoms. Once a CHD3 gene mutation is confirmed, the diagnosis of Snijders Blok-Campeau syndrome is established, providing families with a specific explanation for their child’s developmental differences.

Navigating Life with CHD3 Syndrome

There is no cure for CHD3 syndrome, so management focuses on support and therapy tailored to an individual’s needs. Early intervention is used to address developmental delays from a young age, often involving a multidisciplinary team of specialists.

Therapeutic services are central to managing the condition. Speech therapy helps with communication challenges, physical therapy addresses motor delays and low muscle tone, and occupational therapy assists with developing skills for daily living. For school-aged children, an individualized education plan (IEP) can provide support for learning in an academic environment.

Medical monitoring is also part of life with the syndrome. Some individuals may experience vision problems like farsightedness or misaligned eyes, which require ophthalmological care. In some cases, brain abnormalities or heart conditions may be present, necessitating ongoing monitoring by neurologists or cardiologists.

Prevalence and Scientific Discovery

CHD3 syndrome is an extremely rare disorder. As of 2019, medical literature had identified only about 35 people with the condition worldwide, and its prevalence is estimated to be less than one in a million people. The number of diagnosed individuals is expected to grow as genetic testing becomes more widespread.

The condition was first described in scientific publications in 2018, making it a new diagnosis in genetics. Because the syndrome was recognized recently, the medical community is still in the early stages of understanding the full spectrum of its characteristics and long-term progression.

Research is ongoing, and each new diagnosis contributes to a deeper understanding of how CHD3 gene mutations affect human development. This expanding knowledge is important for improving diagnostic methods and refining therapeutic strategies for families affected by the condition.