Down syndrome

Most rare conditions on this site share one problem: nobody finds them. A child with seizures and delay can be cared for, kindly and competently, for years before anyone orders the one test that names the cause. SYNGAP1-related disorder, elsewhere in this book, is that story.

Down syndrome is its mirror image. It is usually recognised before or at birth, so the label is there from the first day. The risk runs the other way: once a name explains so much, it starts to explain everything. A new silence, a slower walk, a bad night's sleep, a lost skill: each can be filed under the label instead of being looked into. Specialists have a name for this: diagnostic overshadowing, when a known condition casts a shadow that hides a new one, the way a big tree hides the sapling growing under it. Good evidence Experts in Alzheimer's disease in Down syndrome name it directly: dementia is hard to diagnose here partly because its symptoms "are overshadowed by the intellectual disability" (Fortea J et al., Lancet Neurology 2021; PMID 34687637).

None of this is anyone's failure of care. It is a gap in the structure. Life expectancy has more than doubled within one working lifetime, so adults with Down syndrome are a new population. Good evidence The first evidence-based guideline for their medical care appeared only in 2020, and its authors found the evidence base "limited": 22 usable studies, and only one strong recommendation (Tsou AY et al., JAMA 2020; PMID 33079159). Children's care has had a detailed schedule for decades; adult care is still building one. People fall between the two.

The person who closes that gap is usually the primary care doctor (the PCP): the coordinator who knows this person over years, holds the list, and can tell a new change from an old trait. The family's part is to bring the observations, because they see the baseline every day.

Person first. "A man with Down syndrome", not "a Down's patient". The condition is one fact about a person, not the person. In the United States the usual form is "Down syndrome"; in Britain and elsewhere "Down's syndrome" is still common. Both are correct.

• Trisomy 21: three copies of chromosome 21 instead of two, like a recipe written with one ingredient tripled where it called for two. Most people have it in every cell; in mosaic Down syndrome only some cells carry the extra copy; in translocation Down syndrome the extra piece is attached to another chromosome, which matters for family planning.
• Baseline: what is usual for this person, their own normal. Every change is measured against it. A short written note of it (words used, walking, sleep, favourite activities, how they show discomfort) is one of the most useful things a family can keep.
• Atlantoaxial instability: extra looseness between the top two bones of the neck, the ones that let the head turn. Picture a hinge with a worn pin. Usually it causes nothing. Myelopathy is the problem it can lead to: pressure on the spinal cord, like a garden hose being pinched, so signals to the arms, legs, bladder and bowel get through less well.
• Obstructive sleep apnoea: the airway closes over and over in sleep, like a soft straw being sucked flat. The result is broken sleep and daytime tiredness, irritability or behaviour change.
• Down syndrome regression disorder: a loss of skills (speech, self-care, interest) over weeks to months, usually in the teens or twenties, often with freezing or slowed movement. The name dates from a 2022 international consensus Good evidence (Santoro JD et al., Frontiers in Neurology 2022; PMID 35911905).
• Transient abnormal myelopoiesis: a temporary overgrowth of immature blood cells in some newborns with Down syndrome. It usually settles on its own, but it marks a higher later risk of leukaemia.

How to describe a change. "He has stopped going upstairs on his own since about six weeks ago" gives a clinician something to work with. "He's not himself" does not. Say what changed, when it started, and how it differs from the baseline.

Strong evidence Among children with Down syndrome, the American Academy of Pediatrics reports: hearing loss about 75%; obstructive sleep apnoea 50% to 79%; eye problems 60% to 80%; congenital heart defects about 50%; thyroid disease 24% to 50%; coeliac disease 1% to 5%; autism 7% to 19%; symptomatic atlantoaxial instability 1% to 2%; transient abnormal myelopoiesis 4% to 10%; and later leukaemia about 1% (Bull MJ et al., American Academy of Pediatrics, Pediatrics 2022; PMID 35490285).

In childhood Strong evidence the schedule includes an echocardiogram (a heart ultrasound) in the newborn period, a thyroid blood test (TSH) at 6 and 12 months and then yearly, a sleep study for every child between ages 3 and 4, regular hearing and eye checks, and asking about coeliac symptoms at every visit (Bull MJ et al., American Academy of Pediatrics, Pediatrics 2022; PMID 35490285). The sleep-study advice rests on a pooled analysis of 18 studies: with the usual child threshold, about three in four children with Down syndrome had sleep apnoea Strong evidence (Lee CF et al., Journal of Clinical Sleep Medicine 2018; PMID 29734982).

In adulthood Good evidence the 2020 guideline recommends: a thyroid test every 1 to 2 years from age 21; a diabetes test every 3 years from age 30, or every 2 to 3 years from 21 if overweight; weight checked yearly; a yearly question about coeliac symptoms; a yearly review of behaviour and daily function; and, from age 40, a yearly conversation with the person and their caregiver about any change from baseline, to catch early dementia or a treatable condition that looks like it (Tsou AY et al., JAMA 2020; PMID 33079159). It is graded B here because the guideline itself rates most of its evidence as low.

The neck. Good evidence About one adult in ten under 30 shows the looseness on X-ray, yet spinal-cord injury from it is uncommon. Both guidelines therefore advise against routine neck X-rays in people without symptoms. Instead, every year, someone asks and examines for the signs of myelopathy: changed walking, new incontinence, brisk reflexes (Tsou AY et al., JAMA 2020; PMID 33079159); (Bull MJ et al., American Academy of Pediatrics, Pediatrics 2022; PMID 35490285). If those signs appear, the American Academy of Pediatrics calls for neck X-rays and prompt referral to a spine specialist, and for neck-positioning care during any anaesthetic or surgery.

Later life. Strong evidence Alzheimer-type changes start silently: in a study of 388 adults with Down syndrome in Spain and the UK, markers in blood and spinal fluid shifted in the 20s and 30s, memory and thinking changed in the 50s, and symptomatic Alzheimer's disease reached 90% to 100% by the 60s (Fortea J et al., Lancet 2020; PMID 32593336). That long quiet stretch is why the baseline written down at 30 or 35 is so valuable at 45.

This book began with a family in a hospital library, trying to decide whether a child with Down syndrome and leukaemia could take a more intensive chemotherapy. They found a paper suggesting that people with Down syndrome respond differently to these drugs, and it shaped the decision they took with the oncology team. Decades later, checking that memory against the literature taught a sharper lesson than the story alone: the word "resistant" was doing two jobs.

Question one: does the cancer resist the drug? Good evidence In laboratory tests, leukaemia cells from children with Down syndrome behaved very differently by type. Myeloid leukaemia cells were far more sensitive than usual (cytarabine about 12-fold, etoposide about 20-fold). Lymphoblastic leukaemia cells were no more sensitive than in other children, methotrexate included (Zwaan CM et al., Blood 2002; PMID 11756178; DOI 10.1182/blood.v99.1.245).

Question two: does the body tolerate the drug? Good evidence Children with Down syndrome cleared high-dose methotrexate more slowly: blood levels two days after the dose ran roughly double those of matched children, and serious gut and blood-count toxicity was far more common (Garré ML et al., Journal of Pediatrics 1987; PMID 2958611). The study was small, five children. A 2024 review still lists chemotherapy toxicity as a central challenge in treating children with Down syndrome (Barwe SP et al., Blood Reviews 2024; PMID 38016838).

Both at once. Strong evidence In 653 children with Down syndrome and lymphoblastic leukaemia across 16 international trials, relapse was higher (about 26% against 15% at eight years) and treatment-related deaths were higher (about 7% against 2%, mostly from infection) than in other children (Buitenkamp TD et al., Blood 2014; PMID 24222333). So the treating team is weighing two risks that pull in opposite directions. Too little treatment risks relapse; too much risks harm. That is why the answer comes from specialists who know this population, with better supportive care alongside.

The general lesson. Early evidence For any serious medicine, it is worth asking: "Is there evidence specific to Down syndrome for this drug or this disease?" Often there is, in a specialist journal. And "people with Down syndrome are more resistant" or "more sensitive" is never a whole sentence. Resistant to what: the illness, or the side effects? Measured in cells, or in people? No dose in this book is a rule to copy.

Each item below is a pattern to raise, not a diagnosis to make at home.

• Noticed: flinching from a light touch on the neck or shoulders, a new head tilt, a change in walking. Might mean: pain from the neck, or early myelopathy. Would clarify: a neurological examination, then imaging with specialist input. Early evidence Pain may not be put into words: in a Dutch study of 224 adults with Down syndrome, more had painful conditions than controls (50% against 35%), yet fewer reported pain when asked (58% against 73%) (de Knegt NC et al., Pain Medicine 2017; PMID 27694149).
• Noticed: withdrawal, less speech, loss of interest, slowness. Might mean: depression, which in Down syndrome can show as apathy and quietness rather than sadness; or underactive thyroid; or sleep apnoea; or hearing or vision loss. Would clarify: thyroid test, sleep study, hearing and eye checks, a review of recent losses or changes in routine. Good evidence The adult guideline asks clinicians to look for medical causes first whenever mental-health concerns arise (Tsou AY et al., JAMA 2020; PMID 33079159).
• Noticed: in a teenager or young adult, a loss of skills over weeks, with freezing, mutism or sleep upset. Might mean: Down syndrome regression disorder. Would clarify: referral to a neurologist who knows the condition; the 2022 consensus lists the blood, urine, imaging and other tests to run (Santoro JD et al., 2022; PMID 35911905). Good evidence It is worth naming because it can respond to treatment: in an observational study of 212 people, both lorazepam and intravenous immunoglobulin outperformed no treatment over 24 weeks (Santoro JD et al., Neurology and Therapy 2026; PMID 41795763). Treatment was not randomised, so the size of the benefit is uncertain.
• Noticed: repetitive behaviour, little shared attention, or social interest falling below the person's other skills. Might mean: co-occurring autism, found in about one in six people with Down syndrome Strong evidence (Richards C et al., Lancet Psychiatry 2015; PMID 26341300). Would clarify: a specialist autism assessment. Many people with Down syndrome are socially strong, so this is easy to overlook (Bull MJ et al., American Academy of Pediatrics, Pediatrics 2022; PMID 35490285).
• Noticed: coughing or a wet voice at meals, repeated chest infections. Might mean: swallowing difficulty, with food or drink going down the wrong way. Would clarify: a swallow study. Strong evidence Feeding and swallowing problems are reported in 31% to 80% of children with Down syndrome (Bull MJ et al., American Academy of Pediatrics, Pediatrics 2022; PMID 35490285).
• Noticed: constipation that does not respond to the usual measures, especially alongside neck or walking changes. Might mean: thyroid, coeliac disease, or, rarely, the spinal cord. Would clarify: thyroid and coeliac blood tests; a neurological examination if there are other signs. Early evidence The link between symptoms that sit in different specialties (bowel, neck, mood) is easiest to see for the one doctor who holds the whole picture.

Averages are not forecasts. Every percentage here describes a group. It does not predict any one person. Many people with Down syndrome have few of these conditions, and the spread of ability and health is as wide as in anyone else.

Adult evidence is still thin. Good evidence The adult guideline graded most of its own recommendations as weak, for lack of studies (Tsou AY et al., JAMA 2020; PMID 33079159). Where this chapter gives a schedule, it reflects expert agreement more than trial proof. Local practice and a person's own history can reasonably differ.

Laboratory is not bedside. The tenfold and twentyfold drug-sensitivity figures were measured on cells in dishes, not in patients. They explain a direction, not a dose.

Where this came from. Early evidence The founding story in the medicines layer is one family's experience, told without identifying detail. It is included because it shows the questions, not because one outcome proves a rule. Not yet tested Some sources in our own archive state that people with Down syndrome are simply "more drug resistant". That sentence is too broad to stand on its own; the layer above shows the parts that the literature supports.

This chapter is general information for people with Down syndrome, their families and their clinicians. It is not a diagnosis or a treatment plan.

Common, and — past childhood — oddly under-served. Down syndrome (Trisomy 21) changes how the body handles some medicines, some cancers, and some risks. That knowledge largely exists; the gap is that it is often not applied, especially once the person is an adult and paediatric care has ended.

The neck no one checks

Atlantoaxial instability — and the pain nobody hears

Good evidence In 10–30% of people with Down syndrome the ligaments between the top two neck vertebrae (C1–C2) are lax — atlantoaxial instability. It can stay silent until minor strain, and here is the trap: a person with DS may not put pain into words. So the signals are behavioural — flinching or pulling away from a light touch on the neck, new sleep disturbance, a change in walking or new clumsiness, guarding the neck. Neck pain past two weeks, or reflex withdrawal from gentle touch, should be treated as a possible spinal-cord problem until proven otherwise — which means asking for a cervical-spine MRI and a neurologic exam, not reassurance.

Different DNA, different drug response

Research exists; it just is not applied

Trisomy 21 affects several drug-handling pathways, and some cancers behave differently in DS — so a standard protocol is sometimes the wrong one. The founding lesson of this whole project was exactly this: a family’s own library research once turned up a paper showing people with Down syndrome respond differently to a particular chemotherapy, and applying it changed a dosing decision — the child lived, where children with standard genetics on the same high-dose regimen did not all fare as well. Early evidence The general point is solid; the specific dose is never a rule to copy. The move is to ask whether Down-syndrome-specific evidence exists for this medicine or this cancer — because it often does, and is often not reached for.

The screening list adults fall off

Down syndrome carries higher rates of hypothyroidism, coeliac and other autoimmune disease, sleep apnoea, hearing and vision loss, and constipation, with earlier Alzheimer-type change in later life. Each has a DS-specific screening schedule — and adults with DS are exactly where that schedule tends to lapse. Low muscle tone (hypotonia) also makes posture and soft-tissue problems slower to heal. None of this is obscure; it just needs someone keeping the list.

Ask: “Has atlantoaxial instability been assessed — and could these behaviour or sleep changes be neck pain we’re not hearing?” · “Is there Down-syndrome-specific evidence for this medicine or treatment?” · “Are we following a DS-specific screening schedule — thyroid, coeliac, sleep, hearing, vision?” · “What behaviour changes should I treat as a health or pain signal?”

From general clinical literature; the story here carries no identifying detail; not a diagnosis; nothing here comes from any individual’s medical record.

Correction (2 Oct 2026 draft): the 2020 adult and 2022 children’s guidelines give about 1 in 10 adults under 30 with neck-joint looseness on X-ray and 1–2% of children with symptoms; they do not support “10–30%” or a set rule about an MRI after two weeks of neck pain.