Introduction

CDKL5 deficiency disorder (CDD) is a rare, X-linked neurodevelopmental condition that affects brain development and function, primarily due to mutations in the CDKL5 gene. This gene encodes cyclin-dependent kinase-like 5, a protein crucial for early brain development, especially in regulating synaptic function and neuronal communication. The disruption of this protein leads to widespread neurological impairments, including early-onset seizures and profound neurodevelopmental delays.

While the neurological symptoms of CDD are the most widely recognised, many individuals also suffer from a broad spectrum of non-neurological comorbidities that significantly affect their health and daily functioning. The most notable of these involve the gastrointestinal, musculoskeletal (orthopaedic), and visual systems. These manifestations can impact quality of life and require multidisciplinary management approaches.¹

CDD is a lifelong condition with varying levels of severity, although it primarily affects the brain, the downstream effects on other organs and systems highlight the need for comprehensive care. Each patient presents differently, and the pattern and intensity of comorbidities may change over time. Understanding these associated manifestations allows for earlier intervention and better long-term outcomes.

CDKL5 Deficiency Disorder (CDD)

CDD affects an estimated 1 in 40,000 and 60,000 live births worldwide.² Although both males and females can inherit or develop this disorder, females tend to have a higher survival rate due to the protective effect of the second X chromosome.³

Core features of CDD

CDD symptoms typically appear in infancy, often within the first few weeks or months of life, and include:⁴

• Epileptic seizures (often within the first 3 months)
• Global developmental delay
• Intellectual disability 
• Motor dysfunction, including poor head control and a lack of purposeful hand use
• Autonomic dysfunction, such as irregular breathing or temperature rise
• Communication challenges, with many remaining non-verbal 

In many cases, the seizures are refractory to multiple medications and are often misdiagnosed initially as infantile spasms or other early-onset epileptic syndromes. Prompt identification and genetic confirmation are crucial for establishing appropriate treatment plans.

Other associated features may include bruxism (teeth grinding), sleep disturbances, irritability, and increased risk of respiratory infections due to poor coordination of breathing and swallowing.

In addition to these core neurological symptoms, CDD patients often exhibit a constellation of non-neurological comorbidities that require targeted assessment and management. These include issues with the digestive system, musculoskeletal structure, and vision.

Gastrointestinal manifestations in CDKL5 deficiency 

Gastrointestinal (GI) problems are prevalent in individuals with CDD, affecting up to 90% of patients.⁵ The symptoms vary in severity and may persist throughout life. Because many individuals are non-verbal or have limited communication skills, GI issues can be difficult to identify and sometimes misinterpreted as behavioural disturbances or seizure activity.

Key GI issues in CD

Gastroesophageal Reflux Disease (GERD):

GERD is one of the most frequently reported GI issues in CDD. It results from weakened muscle tone in the lower oesophageal sphincter. Symptoms include frequent vomiting, irritability during feeding, coughing, poor weight gain, and discomfort.

Constipation 

Chronic constipation is common and often results from low muscle tone, neurological dysfunction, immobility, and antiseizure medications. It may lead to discomfort, behaviour changes, and decreased appetite.

Feeding difficulties

Many children with CDD have oral motor dysfunction, leading to poor suck-swallow coordination. In moderate to severe cases, nutritional support through gastrostomy tube (G-tube) placement may be required.⁶

Abdominal pain and bloating 

Abdominal discomfort is frequently reported, often due to constipation, motility disorders, or air swallowing. Because many individuals with CDD are non-verbal, pain is sometimes misattributed to seizure activity.

Nutritional deficiencies

Malabsorption, feeding intolerance, and restricted diets may result in deficiencies in key nutrients, including iron, calcium, vitamin D, and overall caloric intake.

Management of GI issues

A multidisciplinary approach is key:³

• Medical: Use of stool softeners, motility agents, and acid reducers
• Nutritional: High-calorie, nutrient-rich diets or elemental formulas
• Surgical: G-tube placement for severe feeding intolerance
• Therapeutic: Involvement of speech and occupational therapists for feeding strategies

Routine abdominal imaging and consultations with a pediatric gastroenterologist can help rule out anatomical abnormalities such as delayed gastric emptying or malrotation.

Orthopaedic (musculoskeletal) manifestations 

Orthopaedic complications are frequent in CDD and are primarily linked to hypotonia (low muscle tone), motor impairments, and abnormal movement patterns.⁷

Common Orthopaedic issues

Scoliosis

Scoliosis, a lateral curvature of the spine, commonly develops in non-ambulatory individuals and can cause pain, postural problems, and compromised lung function.

Hip dysplasia and dislocation

Caused by reduced weight-bearing and abnormal muscle tone, hip subluxation or dislocation is a serious complication that can interfere with comfort and care.

Joint contractures

Prolonged immobility and abnormal posturing lead to joint stiffness and muscle shortening, particularly in the elbows, knees, and ankles.

Osteopenia/Osteoporosis

Antiepileptic drugs, limited mobility, and poor nutrition contribute to decreased bone mineral density, increasing fracture risk.

Management of Orthopaedic issues 

• Physical/occupational therapy: Crucial for maintaining range of motion and mobility
• Orthopaedic interventions: Bracing or surgery for scoliosis and hip dislocation
• Monitoring bone density: Regular DEXA scans and supplementation with calcium and vitamin D
• Adaptive equipment: Wheelchairs, positioning devices, and standing frames

Hydrotherapy and weight-bearing programs, where feasible, are beneficial in improving strength and reducing spasticity.

Visual manifestations in CDKL5 deficiency 

Visual impairments are another hallmark of CDKL5 deficiency. Most individuals are diagnosed with cortical visual impairment (CVI), a condition wherein the brain struggles to process visual information despite normal ocular anatomy.⁸

Common visual issues

Cortical Visual Impairment (CVI)

CVI manifests as reduced visual attention, inconsistent tracking, and difficulty recognising faces or objects. Individuals may respond more to movement or bright light than to complex static scenes.

Strabismus (Crossed Eyes)

This misalignment of the eyes can affect depth perception and visual focus. It often requires surgical correction or the use of eye patches.

Refractive errors

Nearsightedness, farsightedness, and astigmatism (a change in the shape of the eye lens) are common, further complicating visual interpretation in individuals already struggling with cortical processing issues.

Management of visual impairment

• Ophthalmologic exams: Annual reviews by pediatric and neuro-ophthalmologists
• Early intervention: Using vision stimulation and high-contrast tools, and customised therapy programs
• Environmental adjustments: Including visual simplification, increased lighting, and adapted learning materials

Use of visual aids like lightboxes, tablets with visual apps, and consistent routines can enhance visual engagement and learning.

Integrated care and support

Given the multi-system nature of CDKL5 deficiency disorder, a holistic and collaborative approach is critical. Coordination among specialists ensures optimal management. The team often includes:

• Neurologists - seizure management
• Gastrienterologists - feeding, reflux, and motility 
• Orthopaedic surgeons - bone and joint health
• Ophthalmologists - visual assessments
• Dieticians - nutritional planning
• Physical, occupational, and speech therapists
• Social workers and palliative care specialists - family support and care navigation

Beyond medical care, supporting families through counselling, education, financial aid, and community connection is essential to managing the chronic and evolving needs of the child.

FAQs

Can children with CDKL5 walk or speak?

Abilities vary. While some children may achieve limited mobility or use assistive devices, many remain non-verbal and non-ambulatory. Early and intensive therapy can maximise individual potential. Assistive communication devices, such as eye gaze technology or AAC systems, can support language development in non-verbal children.

Is there a cure for CDKL5 deficiency?

No current cure exists. However, research is ongoing into gene therapy, enzyme replacement, and CDKL5-targeted molecular treatments. Current care focuses on symptom control and improving quality of life. Several clinical trials are currently exploring the safety and efficacy of novel therapeutics that target the underlying genetic mutation.

How is CDKL5 diagnosed?

Genetic testing, such as whole-exome sequencing or epilepsy gene panels, confirms the diagnosis. Early diagnosis allows for quicker intervention and family planning.

Newborn screening and increased awareness among paediatricians have contributed to earlier recognition and referral for testing.

Summary

CDKL5 Deficiency Disorder is a complex condition extending far beyond its neurological hallmark of seizures. Children with CDD face significant gastrointestinal, orthopaedic, and visual challenges, which require lifelong, multidisciplinary management.

While no two individuals with CDD are exactly alike, understanding the range of possible comorbidities allows caregivers and healthcare providers to tailor interventions and improve the child’s quality of life.

Early diagnosis, proactive medical care, and tailored support strategies can improve comfort, function, and overall quality of life for both individuals and their families. As research advances, new treatments offer hope for more targeted therapies in the future, reinforcing the importance of awareness and continued investment in care and support.