Slc35a1-cdg is a rare inherited condition that usually begins in infancy and affects the brain, muscles, and blood clotting. Many living with Slc35a1-cdg have developmental delay, low muscle tone, seizures, or feeding problems, and some also have unusual bleeding or bruising. Not everyone will have the same experience, and the early signs of Slc35a1-cdg can range from mild delays to more serious medical problems. Slc35a1-cdg is lifelong, and the outlook depends on how severe it is, with some children facing major health risks while others survive into later childhood or beyond. Treatment for Slc35a1-cdg focuses on supportive care, such as seizure treatment, nutrition support, therapies for development and movement, and careful monitoring for bleeding and other complications.
How many people live with Slc35a1-cdg?
SLC35A1-CDG is so rare that no reliable worldwide estimate has been published; published medical reports describe only a very small number of affected people, and Orphanet does not list a firm global count (Orphanet, 2024). The same is true in the United States, where no trusted estimate is available for how many people are living with it (Orphanet, 2024).
Overview
Slc35a1-cdgSymptoms
SLC35A1-CDG often affects development, movement, and blood clotting. Early signs of SLC35A1-CDG can include low muscle tone, feeding problems, developmental delay, seizures, and unusual bleeding or bruising, though features vary from child to child.
Outlook and prognosis
Slc35a1-cdg often causes lifelong developmental, movement, and blood-clotting problems, but outlook varies widely. Some children have severe disability, while others make gradual gains with therapy and supportive care. Regular follow-up helps manage infections, seizures, and bleeding risks.
Causes and risk factors
SLC35A1-CDG is caused by harmful changes in both copies of the SLC35A1 gene, usually inherited from each parent. Risk is higher with a family history or related parents; lifestyle and environmental factors do not cause it.
Genetic influences
Genetics are central to Slc35a1-cdg, because it is caused by changes in the SLC35A1 gene. Different genetic variations in Slc35a1-cdg can affect severity, so symptoms and day-to-day impact may vary from one person to another.
Diagnosis
SLC35A1-CDG is usually diagnosed by recognizing the pattern of clinical features and checking for supportive lab findings. The genetic diagnosis of SLC35A1-CDG is confirmed with genetic tests, and some people also have imaging or other specialist tests.
Treatment and drugs
Treatment for SLC35A1-CDG focuses on day-to-day needs, such as seizure medicines, feeding support, and physical, occupational, and speech therapy. Regular follow-up helps manage low muscle tone, movement problems, and infections as they change over time.
Symptoms
Signs often begin in infancy or early childhood. For many people with SLC35A1-CDG, the early features of SLC35A1-CDG include delayed milestones, low muscle tone, feeding difficulties, and later learning challenges. Some also have seizures, hearing loss, movement problems, or bleeding issues. Not everyone has the same pattern or severity.
Children with SLC35A1-CDG often sit, walk, and talk later than expected. Speech, learning, and problem-solving can also be affected, so many need extra support at school and in daily life.
Many babies feel unusually floppy and may tire quickly during feeding or play. This can make head control, sitting, crawling, and later walking harder.
Some children have seizures, which may begin in infancy or early childhood. These can look like staring spells, body stiffening, jerking movements, or brief loss of awareness.
Feeding may be slow or difficult, especially early in life. Poor sucking, tiring during feeds, or trouble gaining weight can make growth more challenging.
How people usually first notice Slc35a1-cdg?
The first signs of SLC35A1-CDG are usually noticed in infancy, when a baby may have low muscle tone, feeding difficulties, seizures, or slower-than-expected development. Many living with SLC35A1-CDG also come to medical attention because doctors notice poor growth, a small head size, or unusual blood test results such as low platelets, which can raise concern if there is easy bruising or bleeding. How SLC35A1-CDG is first noticed can vary, but it is most often recognized early in life when several of these problems appear together and lead to genetic testing.
Types of Slc35a1-cdg
No distinct types of Slc35a1-cdg are widely recognized.
Can I slow down the onset of symptoms?
For SLC35A1-CDG, there is currently no good evidence that lifestyle changes or medicines can meaningfully delay when symptoms begin, because this is a rare inherited condition that usually starts very early in life. Good daily care, like treating infections quickly, supporting feeding and growth, and starting physical, occupational, or speech therapy early, may help overall health and day-to-day function, but these steps have not been shown to prevent the condition or postpone its onset; early follow-up with a genetics and neurology team is still important so problems can be spotted and managed promptly. Research is ongoing, and while supportive care can still make a real difference in comfort and development, it cannot yet promise a later start of symptoms.
What genetics can tell you about symptoms
In SLC35A1-CDG, genetics can confirm the diagnosis and give some clues about the pattern of symptoms, but it usually cannot predict the exact course for one individual. Different changes in the SLC35A1 gene can be linked with a range of features, including developmental delay, low muscle tone, seizures, and sometimes blood-related problems, and some variants seem to cause milder or more severe symptoms than others. Because this condition is very rare, doctors still cannot reliably use the gene change alone to say exactly which symptoms will appear or when they will begin.
Causes and risk factors
SLC35A1-CDG is caused by changes in both copies of the SLC35A1 gene, and these are usually inherited from carrier parents. The main risk factor is family history, especially when both parents carry a change in the same gene. In some families, the chance is also higher if the parents are related by blood. Lifestyle and environment do not cause SLC35A1-CDG, but infections, nutrition, and other health problems can affect how strongly symptoms show up. Genetic testing can sometimes clarify your personal risk.
What are the most common causes or risk factors?
SLC35A1-CDG is almost always caused by inherited changes in both copies of a gene called SLC35A1, which helps the body process certain sugar parts needed for normal cell function. The main risk factor is being born to two parents who each carry one changed copy of this gene, so a family history of the condition or parents who are closely related by blood can raise the chance. There are no known lifestyle, diet, or environmental risk factors, so this is not caused by anything a parent did or did not do during pregnancy.
Environmental and biological risk factors
When people look for risk factors for SLC35A1-CDG, the key point is that no well-established environmental or non-genetic biological factors are known to raise the chance of it occurring. Awareness of both biological and environmental influences helps you feel prepared, but for SLC35A1-CDG, factors such as diet, stress, infections, pollution, or routine pregnancy exposures have not been shown to cause it. If this condition is a concern in a family, a medical genetics team can explain what is known and what remains uncertain.
Genetic risk factors
For families trying to understand why SLC35A1-CDG happened, the answer is usually in the genes passed down from both parents. This condition develops when both copies of the SLC35A1 gene are not working as they should. Some risk factors are inherited through our genes. Knowing the genetic causes of SLC35A1-CDG can help with testing, family planning, and understanding chances in future pregnancies.
SLC35A1 changes: SLC35A1-CDG happens when there are harmful changes in the SLC35A1 gene. This gene helps cells attach an important sugar marker called sialic acid to many proteins. When that step is disrupted, several body systems can be affected.
Two altered copies: People living with this condition usually have a disease-causing change in both copies of the SLC35A1 gene, with one inherited from each parent. Having only one altered copy usually does not cause the disorder.
Carrier parents: Parents who each carry one altered SLC35A1 gene are usually healthy and may not know they are carriers. When both parents are carriers, each pregnancy has a 25% chance of SLC35A1-CDG, a 50% chance of a healthy carrier child, and a 25% chance of a child with neither altered copy.
Family history: A brother, sister, or other close relative with the same condition can raise the chance that the gene change runs in the family. This is often one of the clearest clues when doctors consider genetic testing.
Related parents: When parents are biologically related, such as cousins, the chance is higher that both carry the same rare gene change inherited from a shared ancestor. That can increase the risk of recessive conditions like this one, although many affected families are not related.
Lifestyle risk factors
SLC35A1-CDG is an inherited condition, so lifestyle habits do not cause it. However, how lifestyle affects SLC35A1-CDG can matter for day-to-day function, symptom control, and the chance of complications. Because this disorder can affect feeding, growth, development, and sometimes blood cells or immunity, supportive routines are often an important part of care. The main lifestyle risk factors for SLC35A1-CDG are the habits that worsen nutrition, physical conditioning, sleep, infection exposure, and adherence to therapies.
Poor intake, long gaps between meals, or unaddressed swallowing and feeding problems can worsen low energy, poor growth, and weakness in people with SLC35A1-CDG. A structured eating plan and dietitian-guided nutrition may help maintain weight and support development.
Too little movement can worsen deconditioning, stiffness, and delayed motor skills, while overly intense activity may increase fatigue in those with muscle weakness or neurologic symptoms. Regular, adapted exercise and therapy can help preserve mobility and function.
Irregular or poor-quality sleep can aggravate daytime fatigue, irritability, attention problems, and seizure vulnerability in people who are prone to neurologic symptoms. Consistent sleep habits may improve daily functioning and recovery.
Missed hand hygiene, crowded exposure during outbreaks, or delayed attention to early illness can be more problematic if SLC35A1-CDG is affecting immune function or overall resilience. Reducing infection risk may help prevent setbacks in feeding, strength, and development.
Risk prevention
SLC35A1-CDG is a rare inherited condition, so there is usually no way to prevent the disorder itself in someone who is born with it. In practice, prevention focuses on lowering the chance of complications, supporting development, and catching problems early. Some families also want genetic counseling to understand recurrence risk before or during pregnancy. Prevention is flexible—it adapts to your life and health background.
If SLC35A1-CDG has been diagnosed in a child or runs in a family, genetic counseling can help clarify the chance of it happening again. Carrier testing and pregnancy-related testing may be options for some families planning future pregnancies.
Ongoing care with a metabolic or genetics team can help spot issues before they become more serious. This can be especially helpful when early symptoms of SLC35A1-CDG are subtle or overlap with other childhood problems.
Some people with SLC35A1-CDG may be more vulnerable when they get common infections, so routine vaccines, hand hygiene, and quick attention to fevers can help reduce complications. Prevention works best when combined with regular check-ups.
If swallowing is difficult, a feeding evaluation can lower the risk of choking, poor growth, and food or liquid going into the lungs. Thickened feeds or other feeding strategies may help when recommended by the care team.
Can you prevent Slc35a1-cdg?
No, Slc35a1-cdg cannot currently be prevented, because it is a rare inherited condition caused by a gene change that is present from the start of life. If this condition runs in your family, genetic counseling and family testing may help you understand the chance of passing it on and talk through reproductive options, but they do not prevent the condition itself.
Transmission
SLC35A1-CDG is not contagious, so it cannot spread from one person to another through touch, coughing, sex, food, or everyday contact. Instead, how SLC35A1-CDG is inherited is the key issue: it is usually passed down in an autosomal recessive pattern.
This means a child develops SLC35A1-CDG only if they inherit a nonworking copy of the gene from both parents. In most families, each parent carries one changed copy but does not have the condition, and with each pregnancy there is a 1 in 4, or 25%, chance that the child will have SLC35A1-CDG.
When to test your genes
Consider genetic testing if a baby or child has unexplained developmental delay, low muscle tone, seizures, growth problems, or unusual blood clotting or bleeding. Testing is also important when more than one family member is affected or after newborn findings suggest a congenital disorder of glycosylation, because the result can confirm the diagnosis and guide care.
Diagnosis
Slc35a1-cdg is usually diagnosed when a child has a pattern of early health and developmental problems that do not fit a more common condition. Doctors look at the overall picture, including growth, development, muscle tone, blood-related problems, and any unusual findings on exam. Getting a diagnosis is often a turning point toward answers and support. Because this is a rare inherited disorder, the genetic diagnosis of Slc35a1-cdg often combines clinical clues with specialized lab and genetic tests.
Doctors first look for signs that can fit Slc35a1-cdg, such as developmental delay, low muscle tone, feeding problems, seizures, or blood clotting concerns. The pattern of symptoms, along with the child’s exam and medical history, helps raise suspicion for a congenital disorder of glycosylation.
Blood tests may show clues such as anemia, low platelets, or other changes linked to how blood cells are made and function. These tests do not prove Slc35a1-cdg on their own, but they can support the diagnosis and help rule out more common causes.
Specialized lab tests look for abnormal sugar attachment to proteins in the blood, which is a key clue in many CDG conditions. An abnormal result can point doctors toward Slc35a1-cdg and help decide which genetic test to order next.
Genetic tests are used to look for disease-causing changes in the SLC35A1 gene. Finding harmful changes in both copies of the gene can confirm the diagnosis of Slc35a1-cdg in most people.
How is Slc35a1-cdg diagnosed?
Doctors usually suspect SLC35A1-CDG based on a child’s symptoms, growth, and development, then use blood tests that check whether the body is attaching sugar parts to proteins in the usual way. The diagnosis is usually confirmed with genetic testing that looks for disease-causing changes in the SLC35A1 gene, and doctors may also do other tests to rule out similar conditions.
Stages of Slc35a1-cdg
Slc35a1-cdg does not have defined progression stages. This condition is usually described by the pattern and severity of symptoms rather than by clear step-by-step phases over time, and those symptoms can vary a lot from one person to another. Doctors usually start with a conversation about early symptoms of Slc35a1-cdg, such as developmental delays, low muscle tone, feeding problems, seizures, or blood-related concerns, along with a physical exam and routine lab tests. Diagnosis is usually confirmed with genetic testing, and follow-up focuses on tracking day-to-day function, growth, neurologic health, and any complications that need treatment.
Outlook and prognosis
The outlook for people with SLC35A1-CDG is highly variable and depends on how severely the nervous system and other organs are affected. Reported patients often have significant lifelong developmental and neurologic disability, and many need ongoing multidisciplinary care for seizures, movement problems, feeding issues, and recurrent infections or blood-related complications. Because the condition is extremely rare, the long-term prognosis for SLC35A1-CDG is not well defined, and doctors usually estimate outlook based on the individual’s symptoms and how stable they remain over time. Some children survive into later childhood or beyond with supportive treatment, while others with more severe disease can have a poorer course. Mortality data are limited, but early death has been reported in the most severely affected cases, especially when complications are serious.
Long-term effects
For many living with SLC35A1-CDG, the biggest long-term effects involve development, movement, and brain health, and these can shape day-to-day life over many years. Long-term effects vary widely, with some children having severe disabilities early on while others have a milder course. When families ask about the long-term effects of SLC35A1-CDG, doctors usually look at how feeding, growth, seizures, mobility, and learning change over time.
Many people with SLC35A1-CDG have lasting delays in speech, learning, and everyday skills. In more severe cases, a child may need lifelong help with communication, self-care, and school or work activities.
Low muscle tone, poor coordination, and later stiffness can affect sitting, walking, and hand use over time. For many, this can mean needing support for mobility or having ongoing trouble with balance and posture.
Some people with SLC35A1-CDG develop seizures that continue over the long term or are hard to fully control. Ongoing seizures can add to learning and movement difficulties, although severity differs from one person to another.
Feeding problems in infancy may lead to slower growth and continued nutrition concerns later in childhood. Some may find that chewing, swallowing, or gaining weight remains difficult over time.
How is it to live with Slc35a1-cdg?
Living with SLC35A1-CDG can mean managing a rare condition that often affects movement, muscle tone, development, and sometimes blood clotting, so day-to-day life may involve therapies, medical appointments, and extra help with feeding, communication, learning, or mobility. Some people have milder challenges, while others need substantial support, especially if seizures, weakness, or frequent bruising and bleeding are part of the picture. For families and other close caregivers, this can bring a heavy practical and emotional load, but with coordinated care, rehabilitation, and school or community support, many people living with SLC35A1-CDG can build routines that are safer, more comfortable, and more predictable.
Treatment and drugs
SLC35A1-CDG is usually treated with supportive care, because there is no cure yet that fixes the underlying gene change. Treatment often looks different for each person, but it often includes physical, occupational, and speech therapy for developmental needs, plus medicines or other care for problems such as seizures, feeding difficulties, or low blood cell counts if these occur. Many living with SLC35A1-CDG also need regular follow-up with a team that may include a metabolic specialist, neurologist, blood specialist, and nutrition expert, since symptoms can affect more than one body system. For families wondering about the best treatment for SLC35A1-CDG, day-to-day care may also involve watching for infections, bleeding or bruising, and growth or learning concerns so problems can be treated early. Research is ongoing, but for now the main goal is to ease symptoms, support development, and improve quality of life.
Can you cure Slc35a1-cdg?
No, there is currently no cure for Slc35a1-cdg. Because it is a genetic condition, treatment does not remove the underlying cause, but it can help manage symptoms and support daily life, such as with seizure medicine, feeding support, and physical, occupational, or speech therapy. Research is ongoing, but for now care focuses on improving comfort, development, and quality of life.
Non-drug treatment
Daily care for people with SLC35A1-CDG usually focuses on improving movement, communication, feeding, and day-to-day comfort rather than changing the underlying gene condition. Because symptoms can differ a lot from one person to another, treatment is usually tailored with help from a team that may include rehab therapists, feeding specialists, and school support staff. Supportive therapies can make everyday tasks easier and help children build skills over time. For many families, supportive care for SLC35A1-CDG begins with the areas that most affect home life, such as safe eating, mobility, and learning.
Physical therapy can help with low muscle tone, balance problems, and delayed motor skills. Many living with SLC35A1-CDG use it to practice sitting, standing, walking, and safer movement during everyday activities.
Occupational therapy focuses on hand use, play, dressing, and other daily tasks. It may also help with seating, positioning, and simple tools that make eating or schoolwork easier.
Speech and language therapy can support both communication and feeding skills. If speech is limited, therapists may suggest signs, picture boards, or communication devices so children can better express needs and connect with others.
Some people with SLC35A1-CDG have trouble chewing, swallowing, or gaining weight well. Structured programs, like feeding therapy and texture changes, can help make meals safer and support growth.
Your genes may have an impact on how drugs work for you
For people living with SLC35A1-CDG, there are no well-established, condition-specific gene findings that doctors routinely use to predict how common medicines will work. Most treatment is supportive, which means doctors usually choose medicines based on the person’s symptoms, age, liver health, and overall medical needs, then adjust them carefully if side effects or poor response show up. In day-to-day care, this can mean one person does well with a seizure or infection treatment while another needs a different dose or a different medicine, so close follow-up matters more than gene-based drug matching at this time.
Pharmacological treatments
For people living with SLC35A1-CDG, there is no approved medicine that corrects the underlying genetic problem, so treatment usually focuses on symptoms and day-to-day comfort. Drugs are chosen based on the issues a person actually has, such as seizures, muscle stiffness, reflux, or constipation. Not everyone responds to the same medication in the same way, and many living with SLC35A1-CDG need care that is tailored over time.
There is currently no established disease-specific medication for SLC35A1-CDG that fixes the core glycosylation problem. In practice, doctors use supportive medicines based on symptoms rather than one standard drug for everyone.
If seizures are part of SLC35A1-CDG, standard anti-seizure medicines such as levetiracetam, valproate, or clobazam may be used. The best choice depends on seizure type, age, side effects, and what shows up among the early symptoms of SLC35A1-CDG.
For stiffness or spasticity, medicines such as baclofen or diazepam may help relax muscles and reduce discomfort. Some people with abnormal movements may also be considered for treatments such as trihexyphenidyl, depending on their symptoms.
If feeding is difficult because of reflux, doctors may use medicines such as omeprazole or lansoprazole to lower stomach acid. This can make meals less painful and may reduce vomiting or back-arching after feeds.
Genetic influences
For families coping with feeding trouble, low muscle tone, or bleeding issues, it can help to know that SLC35A1-CDG has a clear genetic cause. It happens when a child inherits a changed copy of the SLC35A1 gene from each parent; this gene helps cells add an important sugar called sialic acid to many proteins and fats so they can work properly. A carrier means you hold the gene change but may not show symptoms, which is why parents are usually healthy even though each pregnancy has a 25% (1 in 4) chance of SLC35A1-CDG when both parents are carriers. When both gene copies are not working well, many parts of the body can be affected, which helps explain early symptoms of SLC35A1-CDG such as developmental delay, low muscle tone, or bleeding problems. Understanding how SLC35A1-CDG is inherited can help families make sense of testing results and consider genetic counseling for future pregnancies.
Is Slc35a1-cdg genetic?
Genetics are central to Slc35a1-cdg, because it is caused by changes in the SLC35A1 gene. Different genetic variations in Slc35a1-cdg can affect severity, so symptoms and day-to-day impact may vary from one person to another.
Having a genetic risk is not necessarily a diagnosis
Changes in genes, known as genetic variants, are a normal part of human biology and are common in the general population. Most of these variants do not directly affect health and are simply part of natural human diversity. For many genes, having a variant linked to a condition suggests a possible association rather than a definite diagnosis, especially when multiple genes and environmental factors also play a role. In some cases, though, a single well-understood variant in a specific gene can be enough to confirm a diagnosis.
Pharmacogenetics—how genetics influence drug effects
In SLC35A1-CDG, the underlying gene change helps explain why treatment is usually focused on day-to-day symptoms rather than one medicine that fixes the condition itself. The gene affects glycosylation, a basic cell process used throughout the body, so many living with SLC35A1-CDG need a care plan that may include seizure treatment, feeding support, developmental therapies, and close monitoring for blood or bleeding problems, depending on their symptoms. Not every difference in response is genetic, but the genetic diagnosis is still important because it confirms the exact type of CDG and helps doctors avoid unnecessary tests or treatments that are unlikely to help. At this point, there is no widely established gene-specific drug for SLC35A1-CDG, so the best treatment for SLC35A1-CDG is usually personalized supportive care. In practice, this means doctors choose medicines based on the problems someone has, their age, and how their body is coping overall, rather than a proven drug-gene rule for this rare condition.
Interactions with other conditions
People living with SLC35A1-CDG often have a mix of brain, muscle, feeding, and blood-related problems, so other illnesses can hit harder than they might in someone without the condition. For many, this can mean that common infections, fever, or a stomach bug may bring on more seizures, poorer feeding, dehydration, or a clear drop in energy. If SLC35A1-CDG also causes low muscle tone or trouble swallowing, chest infections and breathing problems may be more difficult to recover from. Doctors also watch closely for low blood counts, easy bruising, or bleeding, because these can complicate infections, surgery, and some medicines. Interactions can look very different from person to person. Since this is a very rare disorder, there is limited research on specific disease pairings, so care usually focuses on preventing complications and making sure specialists coordinate treatment.
How genes can cause diseases
Humans have more than 20,000 genes, each carrying out one or a few specific functions in the body. One gene instructs the body to digest lactose from milk, another tells the body how to build strong bones and another prevents the body's cells from beginning to multiply uncontrollably and developing into cancer. As all of these genes combined are the building instructions for our body, a defect in one of these genes can have severe health consequences.
Through decades of genetic research, we know the genetic code of any healthy/functional human gene. We have also identified that in certain positions on a gene, some individuals may have a different genetic letter from the one you have. We call these hotspots "Genetic Variations" or "Variants" in short. In many cases, studies have been able to show that having the genetic letter "G" in the position makes you healthy, but having the letter "A" in the same position disrupts the gene function and causes a disease. Genopedia allows you to view these variants in genes and summarizes all that we know from scientific research, which genetic letters (Genotype) have good or bad consequences on your health or on your traits.
What other conditions can cause similar symptoms to Slc35a1-cdg?
SLC35A1-CDG can look a lot like other rare inherited conditions that affect how the body handles sugar building blocks on proteins, especially other conditions in the same family called congenital disorders of glycosylation. It can also be mistaken for problems that cause early developmental delay, low muscle tone, seizures, or unusual movements, such as cerebral palsy, mitochondrial disease, or some seizure disorders. Because the symptoms can overlap so much, doctors usually need blood tests and genetic testing to tell them apart.
History
The story of Slc35a1-cdg began only after doctors had better tools to study the sugar chains attached to proteins and fats in the body. In recent decades, awareness has grown around this wider group of conditions, called congenital disorders of glycosylation, as specialists realized that children and families once thought to have unrelated medical problems could actually share the same underlying disorder.
At first, people living with Slc35a1-cdg were recognized mainly by their day-to-day health challenges rather than by a clear laboratory label. A child might come to medical attention because of developmental delay, low muscle tone, seizures, or unusual blood test results, and only later would a broader pattern become clear. As testing improved, doctors were able to connect these features to problems in the body’s handling of sialic acid, an important sugar added near the end of the glycosylation process.
That shift mattered because it turned a confusing set of symptoms into a recognized subtype within the CDG family. Researchers later identified a genetic cause, which helped confirm that Slc35a1-cdg was a distinct condition rather than a loose collection of findings. This also made diagnosis more accurate for families and allowed doctors to better separate Slc35a1-cdg from other CDGs that can look similar at first.
The history of Slc35a1-cdg is still relatively short compared with more common conditions, and much of what is known has come from carefully described case reports and international collaboration. Because it is very rare, each newly reported person can add useful detail about how the condition may appear across infancy, childhood, and beyond. For many families, this growing medical record helps explain why the early symptoms of Slc35a1-cdg can vary from one person to another.
Today, Slc35a1-cdg is understood far better than when the first patients were described, but there is still more to learn. Ongoing follow-up of affected children and adults continues to refine what doctors know about the condition’s course, possible complications, and supportive care needs.