Coffin–Lowry syndrome

Rare X-linked genetic disorder with intellectual disability and skeletal abnormalities

Coffin–Lowry syndrome
Synonyms	CLS, Progressive intellectual and skeletal syndrome
Pronounce	N/A
Specialty	N/A
Symptoms	Intellectual disability, kyphoscoliosis, growth retardation, facial dysmorphism, hypotonia, seizures, cardiac abnormalities
Complications	Hearing loss, visual impairment, cardiomyopathy, scoliosis
Onset	Infancy or early childhood
Duration	Lifelong
Types
Causes	Mutations in the RPS6KA3 gene
Risks	Family history of CLS
Diagnosis	Clinical examination, genetic testing
Differential diagnosis	Fragile X syndrome, Angelman syndrome, Lujan–Fryns syndrome
Prevention	Genetic counseling
Treatment	Supportive care, physical therapy, speech therapy, educational support
Medication	As needed for seizures or cardiac issues
Prognosis	Variable; males typically more severely affected than females
Frequency	1 in 50,000 to 1 in 100,000
Deaths	Rare, often related to severe cardiac or neurological complications

Coffin–Lowry syndrome (CLS) is a rare X-linked dominant genetic disorder characterized by intellectual disability, skeletal abnormalities, delayed development, and distinctive facial features. The condition is more severe in males due to their single X chromosome and typically presents during infancy or early childhood.

Genetic Basis

Coffin–Lowry syndrome is caused by loss-of-function mutations in the RPS6KA3 gene, which encodes the enzyme ribosomal S6 kinase 2 (RSK2). RSK2 is a component of the mitogen-activated protein kinase (MAPK) signaling pathway and is involved in regulating cell growth and development, particularly in the brain and skeletal system.

More than 140 different mutations in RPS6KA3 have been identified, including missense mutations, nonsense mutations, and small insertions or deletions. These mutations impair the normal function of RSK2, leading to disrupted cellular signaling and abnormal development.

Most cases of CLS arise from de novo mutations, meaning the mutation occurs spontaneously in the affected individual with no prior family history. However, in 20–30% of cases, the condition is inherited from a carrier mother. Due to X-inactivation in females, the severity of symptoms can vary. Affected females typically have milder manifestations compared to males, although rare cases of homozygous females have been reported with severe phenotypes.

Clinical Features

The clinical presentation of CLS is variable but typically includes:

• Moderate to severe intellectual disability
• Developmental delay, especially in speech and motor skills
• Distinctive craniofacial features such as a broad nasal bridge, prominent forehead, downward-slanting palpebral fissures, thick eyebrows, wide mouth, and large, soft hands
• Progressive kyphoscoliosis and other skeletal dysplasias
• Hypotonia (reduced muscle tone)
• Stimulus-induced drop episodes (sudden loss of muscle tone after loud noises or emotional stimuli)
• Hearing loss, often sensorineural in type
• Visual impairment, such as cataracts or optic atrophy
• Cardiac abnormalities, including mitral valve prolapse and hypertrophic cardiomyopathy
• Seizures (in a minority of patients)

Diagnosis

Diagnosis of Coffin–Lowry syndrome is based on:

• Detailed clinical evaluation and recognition of characteristic features
• Family history and pedigree analysis
• Genetic testing to identify mutations in the RPS6KA3 gene

Prenatal testing is available when there is a known mutation in the family.

Differential Diagnosis

Conditions that may resemble CLS and should be considered include:

• Fragile X syndrome
• Angelman syndrome
• Lujan–Fryns syndrome
• Aarskog syndrome
• Smith–Lemli–Opitz syndrome

Management

There is no cure for CLS. Management is supportive and involves a multidisciplinary approach:

• Regular monitoring and treatment of cardiac and orthopedic complications
• Speech therapy, physical therapy, and occupational therapy
• Use of hearing aids or cochlear implants if hearing loss is present
• Educational support tailored to cognitive ability
• Antiepileptic drugs for seizure control, if needed
• Genetic counseling for affected families

Prognosis

The prognosis for individuals with CLS varies. While some affected individuals may achieve some level of independence, most require lifelong support. Life expectancy may be reduced in cases with severe cardiac or neurological complications. Females generally have milder symptoms and a better prognosis.

Epidemiology

Coffin–Lowry syndrome is considered rare, with an estimated prevalence between 1 in 50,000 and 1 in 100,000 live births. It affects both males and females, although males are usually more severely affected.

History

The syndrome was first described by Dr. Grange S. Coffin and Dr. Robert B. Lowry in the 1960s and 1970s. Advances in molecular genetics have since clarified the genetic basis of the disorder.

See also

• Genetic disorder
• X-linked dominant inheritance
• Intellectual disability
• Kyphoscoliosis
• Mitogen-activated protein kinase pathway
• Ribosomal S6 kinase
• List of cutaneous conditions associated with internal malignancy

External links

• GeneReviews/UW/NIH entry on Coffin–Lowry syndrome
• http://ghr.nlm.nih.gov/condition/coffin-lowry-syndrome

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