What are the common clinical features of Down syndrome?

Common Clinical Features of Down Syndrome

Virtually all individuals with Down syndrome present with hypotonia and characteristic dysmorphic features, including upslanting palpebral fissures, epicanthal folds, flat nasal bridge, Brushfield spots of the iris, shortened incurving fifth finger, and transverse palmar crease. 1

Neurodevelopmental and Neurological Features

• Intellectual disability is universal, ranging from moderate to severe, making Down syndrome one of the most common genetic causes of cognitive impairment 1
• Hypotonia is present in virtually all individuals and is often one of the earliest recognizable signs 1
• Increased risk of autism spectrum disorder and attention deficit disorder compared to the general population 2
• Epilepsy, particularly infantile spasms, occurs at higher rates and is associated with poor neurodevelopmental outcomes 2
• Alzheimer disease pathology develops universally in adults with Down syndrome, with neuronal degeneration identical to that in the general population 1, 3

Craniofacial and Dysmorphic Features

The most frequently observed characteristic features include:

• Upslanting palpebral fissures 1, 4
• Epicanthal folds 1, 4
• Flat nasal bridge 1, 4
• Brushfield spots of the iris 1
• Protruding tongue 4

Musculoskeletal Features

• Transverse palmar crease (simian crease) 1, 4
• Sandal gap (increased space between first and second toes) 4
• Shortened, incurving fifth finger (clinodactyly) 1
• Joint laxity and dislocations 5
• Atlantoaxial subluxation and upper cervical spine instability 5

Cardiovascular Manifestations

• Congenital heart disease occurs in 40-60% of infants, with septal defects (particularly atrioventricular canal defects) being most common 1, 2, 5
• Persistent pulmonary hypertension of the newborn develops in 5-34% of infants, even in those without congenital heart disease 2
• Approximately 48.9% require cardiac surgical repair 6

Gastrointestinal Abnormalities

• Gastrointestinal anomalies occur in 5% of cases 1
• Duodenal atresia is a characteristic association 1, 5
• Hirschsprung disease 1, 5
• Anal atresia 5
• Feeding problems are present in 42-49.7% of children 6
• Dysphagia affects 26.2% 6

Respiratory Complications

• Obstructive sleep apnea is highly prevalent, affecting 56.8% of children 6
• Recurrent lower respiratory tract infections 2
• Aspiration risk is increased 2
• Pulmonary hypoplasia may be present 5
• Oxygen requirement affects 53.7% of neonates 6

Hematologic and Oncologic Features

• Childhood leukemia incidence is increased 18-20 fold compared to the general population 1, 5
• Paradoxically, solid tumors occur at lower rates than in the general population 3

Endocrine Abnormalities

• Thyroid dysfunction is common throughout childhood and adulthood 2, 7
• Diabetes mellitus occurs at increased rates 2
• Increased weight gain is frequently observed, particularly during adolescence 7

Sensory Impairments

• Hearing deficits are well-recognized associations 2
• Visual impairment is common 2, 7
• Congenital cataracts may require immediate attention 7
• Keratoconus affects 3.6% 6

Autoimmune and Immunologic Features

• Autoimmune diseases occur at higher rates 2
• Celiac disease is more common 2
• Arthropathy 2
• Infectious diseases occur with increased frequency during childhood 7

Dermatologic Manifestations

• Skin infections are more common, particularly during adolescence 7
• Various dermatological conditions occur at increased rates 2

Neonatal Complications

• 80% of newborns require NICU admission 6
• Respiratory distress syndrome affects 14.7% 6
• Feeding problems are present in 49.7% of neonates 6

Important Clinical Caveats

Mosaic Down syndrome (3.85% of cases) presents a diagnostic challenge, as only 37.5% are diagnosed clinically based on physical features, compared to 90% of trisomy 21 cases 4. These individuals may lack obvious dysmorphic features and should be considered in any person with unexplained intellectual disability 4.

The six most common features (simian crease, sandal gap, epicanthic folds, hypotonia, upslanting palpebral fissures, and protruding tongue) can also appear in karyotypically normal individuals, potentially causing unnecessary parental anxiety 4. Therefore, karyotyping remains the definitive diagnostic test 1.

Prognosis

Individuals with Down syndrome without congenital heart disease can live beyond 60 years of age 1, though accelerated aging and Alzheimer disease pose significant challenges in adulthood 3, 7.