Symptoms, Behavior & Development in KdVS

As you navigate a diagnosis of Koolen-de Vries Syndrome (KdVS), it is helpful to look beyond the clinical labels and see the unique “personality” of this syndrome. While every child is an individual, there is a remarkably consistent pattern of development and behavior that characterizes KdVS. Many parents find that their children are among the most social and affectionate individuals they know, often described as having a “sunnier” outlook on life than their peers ^[1][2].

Movement and the “Floppy” Baby

One of the earliest signs of KdVS is neonatal hypotonia, or low muscle tone ^[3][4]. In infancy, this may make a baby feel “floppy” when held and can lead to difficulties with feeding or sucking. If this occurs, early involvement of a feeding therapist and the use of specialized bottles can be highly beneficial ^[3][4]. This low muscle tone is the primary reason for delays in gross motor skills (like sitting up, crawling, and walking) and fine motor skills (like grasping toys or using a spoon) ^[4][5].

Because the muscles have to work harder to stabilize the body, physical therapy is often a cornerstone of early intervention. It is also important to monitor for scoliosis (curvature of the spine), as the same low muscle tone that affects movement can also impact the alignment of the back as a child grows ^[6][1].

The Heart of KdVS: A Friendly Disposition

Perhaps the most striking feature of KdVS is the behavioral phenotype—a term used by doctors to describe the typical behaviors associated with a genetic condition. Children with KdVS are famously sociable, outgoing, and friendly ^[1][2]. Even when facing significant intellectual or communication challenges, their desire to connect with others remains a core strength ^[2].

While this sociability is a wonderful trait, it can sometimes mask the underlying intellectual disability, which typically ranges from mild to moderate ^[1][7]. Some parents also notice that while their children are social, they may still struggle with self-regulation or anxiety, particularly as they transition into new environments or face higher social demands ^[2][8].

The Speech Gap: Words vs. Understanding

Speech and language impairment is a core feature of KdVS, and it often follows a specific pattern ^[9][10]. Most children experience a significant gap between:

• Receptive Language: What they understand (which is often surprisingly high).
• Expressive Language: What they can actually say (which is often severely delayed).

First words often do not appear until after age 3, and some children take longer ^[11][10]. This delay is often caused by apraxia (difficulty planning the mouth movements for speech) or dysarthria (muscle weakness affecting speech) ^[12][11].

Because these children are so social and want to communicate, the inability to speak can be frustrating. This is why experts strongly advocate for Augmentative and Alternative Communication (AAC) ^[9][10]. AAC is not just high-tech devices; it also includes recognizing and validating natural gestures and body language, as well as formal tools like:

• Sign language
• Picture exchange systems (PECS)
• Speech-generating devices (tablets with communication apps)

Using AAC does not stop a child from talking; rather, it provides a “bridge” that allows them to share their thoughts and social nature while their verbal speech develops ^[10][13].

Distinctive Physical Traits

Children with KdVS often share a “family resemblance” to one another. Common facial features include:

• A pear-shaped nose with a bulbous or overhanging tip ^[1][3].
• A long face with a high forehead ^[1].
• Large or prominent ears ^[1].
• Up-slanting eyes, often with ptosis (droopy eyelids) or strabismus (crossed eyes) ^[14][15].

Health Considerations to Watch For

In addition to developmental traits, there are several medical areas that require monitoring:

• Epilepsy: About 50% of children with KdVS develop seizures, which often begin around age 3 or 4 ^[5][8].
• Vision: Many children have vision issues like far-sightedness (hyperopia) that require glasses ^[14].
• Growth: After puberty, there is an increased risk for becoming overweight or obese, so healthy nutritional habits are important to establish early ^[2][1].