Down syndrome produces a recognizable pattern of physical features, developmental differences, and associated health conditions that range from mild to significant. About 1 in every 640 babies born in the United States has Down syndrome, making it the most common chromosomal condition. Not every person with Down syndrome has the same symptoms or the same severity, but the overall pattern is consistent enough that many signs are visible at birth.
Physical Features Visible at Birth
Most babies with Down syndrome are identified shortly after delivery based on a cluster of physical characteristics. These include a flattened facial profile and nose, eyes that slant upward, and a skin fold covering the inner corner of each eye. Newborns also tend to have decreased muscle tone, which makes them feel noticeably floppy when held. A single deep crease running across the palm of the hand, rather than the typical two creases, is another classic sign.
Other common features include a shorter neck, small ears, a tongue that may protrude from the mouth, and small hands and feet with a wider gap between the first and second toes. No single feature confirms Down syndrome on its own. Doctors look for a combination of these traits and confirm the diagnosis with a blood test that examines the chromosomes.
There are three genetic types of Down syndrome, but the physical features and behaviors overlap across all three. People with the mosaic form, where only some cells carry an extra chromosome, may have fewer or milder physical features.
Developmental Milestones and Timing
Children with Down syndrome reach the same developmental milestones as other children, but on a significantly different timeline. A large study published by the American Academy of Pediatrics tracked when 75% of children with Down syndrome achieved specific skills, offering families a realistic picture of what to expect.
For motor skills, most children sit unsupported by about 1.2 years. Walking independently around the home happens by around 4.5 years for 75% of children. Running comes closer to age 8, and using stairs independently follows around 8.5 years. These numbers are averages, and many children fall on either side.
Speech develops more slowly than motor skills. About 75% of children use at least one word, sign, or picture by 1.5 years, but using two-word phrases takes until about age 7.7 for that same threshold. Following simple one-step directions is typical by 5.6 years, while two-step directions take until nearly age 15. Building a vocabulary of 50 or more words, signs, or pictures reaches the 75% mark at 15.8 years. Conversational speech develops gradually: only about 15% of children hold conversations by age 7, rising to roughly 60% by age 21.
Toilet training during the day follows a wide range. About 15% of children are trained by age 4, 75% by age 9, and 90% by age 12. These timelines can help families set realistic goals and measure progress in a meaningful way.
Intellectual Disability
Nearly all people with Down syndrome have some degree of intellectual disability, typically in the mild to moderate range. This affects reasoning, problem-solving, and the ability to learn new concepts, but the range is wide. Some individuals live and work with a high level of independence, while others need more daily support throughout their lives.
Cognitive strengths often include visual learning and social understanding. Many children with Down syndrome are described as social and motivated by relationships, which can be a real advantage in educational and therapeutic settings. Memory for routines tends to be strong, while abstract thinking and processing spoken language are typically more challenging.
Heart Defects
About half of all babies born with Down syndrome have a congenital heart defect. A pooled analysis of over 60,000 individuals found the prevalence to be 49.9%. The most common types involve holes or malformations in the walls separating the heart’s chambers. These are often detected by ultrasound before birth or by physical exam and testing shortly after.
Many of these heart defects require surgical repair in the first year of life. Some are minor and close on their own or need only monitoring. Because heart problems are so common, all newborns with Down syndrome receive a cardiac evaluation, typically an echocardiogram, within the first few weeks.
Sleep Apnea
Obstructive sleep apnea is strikingly common in children with Down syndrome. Studies report prevalence rates between 45% and 83%, far higher than in the general pediatric population. The combination of low muscle tone, a smaller airway, and a relatively large tongue creates conditions where the airway partially or fully collapses during sleep.
Signs to watch for include loud snoring, pauses in breathing, restless sleep, unusual sleep positions (like sleeping sitting up or with the neck hyperextended), and daytime sleepiness or irritability. Because sleep apnea can affect behavior, learning, and heart health, sleep studies are recommended for children with Down syndrome even if symptoms aren’t obvious.
Thyroid Problems
Thyroid dysfunction occurs at much higher rates in people with Down syndrome than in the general population. About 11% to 13% have significant thyroid underactivity, either present at birth or developing later in childhood. An underactive thyroid slows metabolism and can cause fatigue, weight gain, constipation, and dry skin. Because these symptoms overlap with features of Down syndrome itself, thyroid problems can be easy to miss without regular blood testing. Most guidelines recommend checking thyroid levels at birth and annually throughout life.
Behavioral Patterns
Children with Down syndrome are often warm and socially oriented, but behavioral challenges are common. Impulsivity, difficulty with transitions, and a strong preference for routine can lead to stubbornness or refusal behaviors. “No” tends to be a favorite word. Some children have little sense of danger and may run away in unfamiliar settings, which creates real safety concerns for families.
These behaviors are tied to underlying differences in how the brain processes information. Slower processing speed, difficulty understanding complex verbal instructions, and sensory sensitivities all contribute. Behavioral challenges tend to improve with consistent structure, visual supports, and therapies tailored to each child’s profile.
Vision and Hearing
Vision problems are common in Down syndrome. Refractive errors like nearsightedness and farsightedness affect a large proportion of children, and conditions like crossed eyes and cataracts occur at higher rates than in the general population. Regular eye exams starting in infancy help catch problems early, since uncorrected vision issues can compound learning difficulties.
Hearing loss is also frequent, affecting a significant number of children with Down syndrome. It can be present at birth or develop over time due to fluid buildup in the middle ear, a consequence of the smaller ear canals typical of the condition. Even mild hearing loss can interfere with speech development, making routine hearing screenings essential.
Life Expectancy
Life expectancy for people with Down syndrome has improved dramatically. As recently as 1983, the average life expectancy was 25 years. By 2007, it had risen to about 47 years, driven largely by advances in heart surgery and better medical care throughout childhood. Many adults with Down syndrome now live into their 50s and 60s. Early-onset Alzheimer’s disease is a significant concern as people age, with symptoms appearing earlier than in the general population, often in the 40s or 50s.