Introduction

Overview of hanhart syndrome

Definition and rare nature of the condition

Hanhart Syndrome is a rare congenital disorder characterised by an underdevelopment of the mouth, jaw and limbs. It is part of a larger family of syndromes known collectively as oromandibular-limb hypogenesis syndrome (OLHS) and is often called hypoglossia-hypodactylia syndrome. Whilst the syndrome itself doesn't have any obvious implications for the brain, physical factors related to the syndrome can indirectly impact early cognitive development. Hypoglossia is a pathology and refers to a short or incomplete tongue.¹ Hypodactylia refers to the presence of fewer than 5 fingers or toes.² Hanhart syndrome is commonly diagnosed at the neonatal stage during clinical evaluation.³

Causes and symptoms of hanhart syndrome

Genetic and environmental factors

Genetics

The exact cause of Hanhart syndrome is unknown, with both genetic and environmental factors thought to be the source. The syndrome is often referred to as ‘sporadic,’ occurring in scattered patterns, with no apparent cause.¹ However, there are some researchers who believe that instances of the Hanhart syndrome occur within children of affected relatives, inherited in an autosomal recessive manner. A condition is described as recessive when both parents must be carrying the corresponding gene in order for the condition to manifest.

Environmental contributors or unknown factors

Another theory concerning the cause of Hanhart syndrome is that abnormalities during the developmental process, brought about by interruptions to the blood supply to parts of the embryo that would eventually give rise to the extremities, tongue, jaw and mouth. ¹ Interruption of the blood supply can occur due to many reasons.

Importance of studying cognitive development in hanhart syndrome

Understanding the impact on mental and intellectual growth

Cognitive development refers to the development of cognition, the action or process by which we acquire knowledge and understanding through experiences, giving one a perception or sensation of the world around us. The way in which Hanhart Syndrome impacts cognitive development is indirect, being the consequence of the condition’s physical symptoms. As a result, the influence of Hanhart Syndrome on cognition can be difficult for individuals and their families to understand.

Differentiating physical from cognitive symptoms

It's important to differentiate physical symptoms from cognitive ones. Physical symptoms involve the limbs, craniofacial and oral abnormalities such as misshapen limbs and fingers, short or absent tongues and smaller jaws.

On the other hand, cognitive symptoms involve the delayed onset of speech due to the physical oral or jaw abnormalities that directly affect the ability to articulate words. This can cause impairment of language development. To further elaborate, speech and language are major elements in cognitive development, such that their impairment influences social interaction and communication, thereby affecting learning and leading to a delay in intellectual growth as a result.⁴

Limb abnormalities also play a major role in cognitive development. Just as the brain can send signals out to the body, the body can also, in turn, send signals back to the brain. An abnormality in the limbs can affect fine motor skills, such as carrying out tasks using the smaller muscles in the hands, which are related to cognitive functions like problem-solving, spatial awareness and learning.

Developmental milestones can also be delayed, involving motor skills, such as walking, grasping and moving objects, greatly contributing to delayed cognitive development.

Challenges in assessing cognitive development

Since Hanhart syndrome does not influence the architecture of the brain, there is an absence of neurological markers related to cognitive functions found in the brain of an individual with the syndrome.

Difficulty separating cognitive delays due to the syndrome vs other factors, e.g. speech challenges

Assessing cognitive development comes with challenges. Since Hanhart syndrome is often diagnosed during the neonatal or infant stages, there is a difficulty in that the inability to speak or perform tasks can be mistaken for cognitive delay. Additionally, there are other speech challenges which may share similarities to those seen in Hanhart syndrome. As a result, Hanhart syndrome is diagnosed based on extensive evaluation and physical findings.

Limited case studies and small sample sizes

Since Hanhart syndrome is an extremely rare condition, with an incidence of less than 1 in 20,000 births, there are a very limited number of case studies to support the development of diagnostic tools, treatments and understanding of the syndrome.³

Cognitive development interventions and therapies

Speech and language therapy

Speech and language are pivotal for cognitive development. As mentioned previously, any disruption of these can cause developmental delays, preventing an individual from reaching certain milestones.

Language ensures that various cognitive functions such as memory, attention and problem-solving develop. In their absence, cognitive skills do not evolve, leading to a negative impact on intellectual growth.

Since the physical aspects of Hanhart syndrome can impact language, it can be assumed that communication and social interaction are also impacted. Communication allows an individual to understand and interact with their counterparts, ensuring the development of social cognition. Such skills are vital for navigating relationships and building intimate social environments, feeding into cognitive and emotional development. A delay in speech and language may cause a person to struggle during social interaction, thus limiting exposure to the learning aspects of social engagement.

Techniques used to aid communication

Speech and language therapy can aid communication and support cognitive development, which is further enhanced by being introduced early in life. Examples of techniques used are:⁵

• Interactive play-based therapy
• Augmentative and alternative communication (AAC)
• Repetitive language practice and cognitive exercises

Importance of early intervention

It should be noted that there is a significant emphasis on introducing therapeutic interventions early in life. This not only ensures that cognitive delays can be prevented but also builds a foundation for lifelong learning and improves the ability to adapt to emotional and social situations.

Physical and occupational therapy

Physical and occupational therapies aim to improve motor-cognitive connections such as brain-body integration and cognitive development through movement. Brain-body integration refers to the learned behaviour of a child to control their body, along with developing cognitive skills such as spatial awareness. Cognitive development through movement occurs during activities which involve physical actions, helping an individual to understand their environment. Since physical action is linked to cognitive development, a breakdown in physical development can, in turn, affect cognition and delay developmental milestones since an individual can miss out on learning opportunities.

Techniques used to support cognitive development include:

• Occupational therapy
• Physical therapy

Summary

Hanhart syndrome is a rare disorder with the precise cause remaining unknown. The disorder does not directly affect the brain; rather, its features, namely the absent or incomplete tongue and malformation of the extremities, indirectly affect cognitive development. As of right now, there is no permanent cure for Hanhart syndrome, but many supportive therapies exist to improve the life of an individual with the condition. Therapies focus on speech and language as well as physical and occupational therapy to assist with the physical aspects of Hanhart syndrome, thus aiding cognitive development.