Snijders Blok–Campeau syndrome

Snijders Blok–Campeau syndrome is a genetic disorder caused by mutations in the CHD3 gene.^[1] It is characterized by impaired intellectual development, macrocephaly, dysarthria and apraxia of speech, and certain distinctive facial features.^[2]

Snijders Blok–Campeau syndrome
Other names	SNIBCPS, IDDMSF
An image displaying 18 individuals who have Snijders Blok-Campeau syndrome
Symptoms	Intellectual disability, Macrocephaly, distinctive facial features
Usual onset	Before birth
Duration	Life long
Causes	Mutations in the CHD3 gene
Frequency	Approximately 60 cases described in scientific literature, with an estimated 150 diagnosed worldwide

Snijders Blok–Campeau syndrome is typically a de novo mutation^[3][4] which generally occurs during the early embryonic stages of development or during the formation of the parent's reproductive cells.^[2] This allows for prenatal diagnosis.^[5]

Signs and symptoms

Snijders Blok–Campeau syndrome almost always comes with both physical and intellectual disabilities. Those with the condition will typically have trouble in the development of speech and language. Around one half typically have some form of macrocephaly, while around one third show signs of autism or similar conditions.^[4]

Characteristics	Percentage	Characteristics	Percentage
Developmental disorder	100%[3][6]	Flexible ligaments	40%[3]
Speech delay or disorder	100%[3][6]	Central nervous system abnormalities	39%[6]
Intellectual disability	95%[6]	Male genital abnormalities	35%[3]
Low muscle tone	92%[6]	Autism or autism-like features	33%[6]
Large or prominent forehead	85%[3]	Neonatal feeding problems	31%[3]
Widely spaced eyes	77%[3]	Strabism	30%[3]
Visual abnormalities	75%[6]	Seizures	21%[6]
Thin upper lip	74%[6]	Congenital heart disease	21%[6]
Broad nasal bridge	71%[6]	Missing teeth	16%[6]
Macrocephaly	58%[3]	Hearing loss	13%[6]
Deep set eyes	54%[6]	Microcephaly	5%[6]

Cause

The CHD3 gene is required for chromatin remodeling, a process that regulates gene expression.^[7] By allowing for the creation of chromatin, the CHD3 gene affects how tightly DNA is packed into chromosomes. A mutation of the CHD3 gene changes the amount of chromatin produced, causing over or underexpression of other genes.^[7][8]

History

Due to the rarity of the condition, with only approximately 60 cases documented in scientific literature,^[7] Snijders Blok–Campeau syndrome was only discovered in 2018 by clinical geneticist Lot Snijders Blok and clinician-scientist Philippe M Campeau. The mutation was first documented in the paper "CHD3 helicase domain mutations cause a neurodevelopmental syndrome with macrocephaly and impaired speech and language".^[3]