Monosomy 22q13.3 is a genetic condition caused by missing DNA at the end of chromosome 22. People with Monosomy 22q13.3 often have low muscle tone, developmental delay, and limited or absent speech. Many also have feeding challenges, sensory differences, and behaviors seen in autism spectrum, and doctors may notice slower growth. Signs begin in infancy and the condition is lifelong, but not everyone will have the same experience. Care focuses on supportive therapies, seizure and sleep management if needed, and regular follow-up, and the outlook varies but many people live into adulthood.
Overview
Monosomy 22q13.3Symptoms
Monosomy 22q13.3, also called Phelan‑McDermid syndrome, mainly features global developmental delay, very limited or absent speech, and low muscle tone. Early signs can include feeding difficulties, poor eye contact, autism‑like behaviors, decreased pain sensitivity, sleep problems, and sometimes seizures.
Outlook and prognosis
Many living with Monosomy 22q13.3 grow slowly and reach milestones later, but progress continues across childhood and adulthood with tailored therapies. Epilepsy, low muscle tone, and feeding or breathing issues often stabilize with consistent care. Lifespan can be near typical, especially with early intervention and close monitoring of seizures, sleep, and infections.
Causes and risk factors
Monosomy 22q13.3 results from a missing segment of chromosome 22, usually a new (de novo) change before birth. Risk increases when a parent carries a balanced translocation or mosaic change; deletion size influences features. No proven lifestyle or environmental triggers.
Genetic influences
Genetics is central in Monosomy 22q13.3: it results from missing genetic material at the end of chromosome 22. Most cases are de novo, though some come from a balanced parental rearrangement. Genetic testing clarifies the deletion size, inheritance risk, and family planning.
Diagnosis
Diagnosis of Monosomy 22q13.3 starts with clinical features, then confirmation by genetic testing. Chromosomal microarray or targeted testing detects a 22q13.3 deletion. This approach supports the genetic diagnosis of Monosomy 22q13.3 and helps guide care.
Treatment and drugs
Treatment for Monosomy 22q13.3 focuses on supportive care tailored to each person’s needs. Care teams often combine early developmental therapies, speech and communication support, seizure management if needed, nutritional and feeding plans, and sleep or behavior strategies. Regular hearing, vision, heart, kidney, and orthopedic checks guide adjustments over time.
Symptoms
Many families first notice delays in movement and speech, softer muscle tone, and feeding challenges in infancy. Early on, this might look like a baby who feels floppy, tires easily during feeds, and takes longer to sit, crawl, or say first words. As children grow, social communication differences, sensory seeking, sleep problems, or seizures can appear. These are common features of Monosomy 22q13.3; if you’re wondering about early features of Monosomy 22q13.3, they often center on movement, feeding, and language.
Sitting, crawling, and walking may happen later than in other children. Climbing stairs or keeping up on the playground can take extra effort. Physical therapy often helps build skills over time.
Babies may feel “floppy,” with loose joints and less body stability. Clinicians call this hypotonia, which means muscles feel looser and tire more easily. It can affect posture, chewing, and drooling.
Many with Monosomy 22q13.3 have few spoken words or none. Understanding language is often stronger than speaking. Picture boards or speech devices can open up communication.
Eye contact, gestures, and back-and-forth interaction may be limited. Repetitive interests or routines are common. These traits overlap with autism spectrum features.
How people usually first notice Monosomy 22q13.3?
Families often notice the first signs of Monosomy 22q13.3 (also called Phelan-McDermid syndrome) in early infancy as low muscle tone that makes a baby feel “floppy,” along with feeding difficulties and delayed milestones like rolling or sitting. As months pass, many see limited babbling or words, reduced eye contact, and sensory differences, prompting early referral to developmental services; doctors may also note larger head size, decreased pain sensitivity, or subtle facial features. Confirmation usually comes later through genetic testing after concerns about global developmental delay or autism features, which is how the first signs of Monosomy 22q13.3 are often recognized.
Types of Monosomy 22q13.3
People living with Monosomy 22q13.3 can have different patterns of challenges, from developmental delays to medical issues that vary in severity. Researchers describe these categories to better understand patterns of the condition. Not everyone will experience every type. When learning about types of Monosomy 22q13.3, it helps to focus on well-recognized genetic variants rather than symptoms alone, since these variants can influence how early symptoms of Monosomy 22q13.3 appear and how strong they are.
Terminal deletion
A segment at the very end of chromosome 22’s long arm is missing. This is the most common variant and often links to low muscle tone, speech delay, and developmental differences. Larger deletions generally correlate with more pronounced features.
Interstitial deletion
A middle section of 22q13.3 is missing while the chromosome ends remain. Symptoms can overlap with terminal deletions but may be milder or more specific depending on which genes are involved. The exact size and location often shape learning and communication impacts.
Ring chromosome 22
The chromosome forms a ring after breaks at both ends, sometimes losing 22q13.3 material. People may have developmental delay, reduced muscle tone, and seizures, with variability tied to how stable the ring is in cells. Mosaicism can lead to a broader range of severity.
Unbalanced translocation
Extra or missing material occurs because chromosome 22 swaps segments with another chromosome and the exchange is uneven. Features depend on both the lost 22q13.3 region and any gained material from the partner chromosome. Parental chromosome studies can clarify recurrence risk for families.
SHANK3-only deletion
The missing region mainly involves the SHANK3 gene within 22q13.3. This variant often centers on speech and social-communication challenges with relatively fewer medical complications. Motor tone and sensory differences may still be present.
Mosaic deletions
Only a portion of cells carry the 22q13.3 loss, while others are typical. Severity can be reduced compared with non-mosaic forms, though it varies with the percentage of affected cells. Testing different tissues can sometimes reveal mosaic patterns.
What genetics can tell you about symptoms
Some people with monosomy 22q13.3 (also called Phelan‑McDermid syndrome) have missing SHANK3 gene material, which can lead to low muscle tone, delayed speech or absent speech, sensory differences, and autistic features. Larger deletions on 22q13.3 can add seizures, feeding problems, and more significant developmental delays.
Causes and risk factors
Most cases start with a new change in the egg or sperm, where a small end piece of chromosome 22 is missing.
The genetic causes of Monosomy 22q13.3 most often involve a missing segment that includes the SHANK3 gene.
Less often, a parent carries a balanced chromosome rearrangement or low level mosaic change, which can raise the chance of having a child with Monosomy 22q13.3.
There are no known lifestyle, diet, or pregnancy exposures that cause it, and most families have no history.
Genes set the stage, but environment and lifestyle often decide how the story unfolds.
Environmental and biological risk factors
Families often want to know what might raise the chance of Monosomy 22q13.3 occurring. Because early symptoms of Monosomy 22q13.3 can be subtle, questions about risk come up early. Doctors often group risks into internal (biological) and external (environmental). Most cases appear unexpectedly with no clear trigger.
Many cases result from a chance loss of chromosome material at conception. This biological event is not caused by anything parents did. Most Monosomy 22q13.3 cases appear to occur this way.
Older maternal age clearly raises risk for whole-chromosome conditions, but a consistent link to this microdeletion has not been shown. Monosomy 22q13.3 can occur at any maternal age.
Advanced paternal age can increase some new DNA changes in sperm. A clear association with the 22q13.3 terminal loss has not been demonstrated. Risk appears across paternal age groups.
Ionizing radiation can break DNA and raise the chance of chromosomal errors in cells. Medical imaging in pregnancy usually uses low doses and shielding to keep exposure minimal.
Genetic risk factors
Monosomy 22q13.3 usually happens when a piece from the long arm of chromosome 22 is missing, often including a gene called SHANK3. Most cases start as a new change at conception, but some are inherited through a family chromosome rearrangement. Some risk factors are inherited through our genes. Understanding the genetic causes of Monosomy 22q13.3 can help clarify recurrence risk for future pregnancies.
De novo deletion: A new deletion at 22q13.3 can arise in the egg, sperm, or just after fertilization. It is not typically inherited and usually means a low chance of it happening again. Genetic counseling can explain the small but real possibility of recurrence due to hidden mosaicism.
SHANK3 loss: Many deletions remove the SHANK3 gene, which is important for brain cell connections. Losing SHANK3 helps explain common features in people with Monosomy 22q13.3. Testing can show whether SHANK3 is included in the missing segment.
Balanced translocation carrier: A parent may carry a balanced swap of chromosome pieces that causes no symptoms. When passed to a child, it can become unbalanced and produce a 22q13.3 deletion. This raises the chance of having another affected child.
Ring chromosome 22: Rarely, chromosome 22 forms a circle after its ends break and join. This can delete 22q13.3 and lead to mosaic or full monosomy. If a parent carries a ring 22, recurrence risk is higher.
Unbalanced rearrangement: An unbalanced derivative chromosome can include missing 22q13.3 material along with extra material from another chromosome. The result is Monosomy 22q13.3 plus possible duplication from the partner chromosome. Families may notice variable findings depending on which segments are involved.
Parental mosaicism: A parent may have the deletion in only some cells or only in eggs or sperm. The parent may be healthy, but the chance of recurrence is higher than in a fully de novo case. Specialized tests may be needed to detect low-level mosaicism.
Interstitial microdeletion: Instead of the very end, a small internal piece of 22q13.3 can be missing. This can still remove key genes and cause Monosomy 22q13.3. Most arise as new changes with low recurrence risk.
Genomic fragile spots: Repetitive DNA near 22q13 can make the region prone to breaks. These natural hotspots can set up a deletion without any trigger from outside the body. This helps explain why many cases are sporadic.
Lifestyle risk factors
Monosomy 22q13.3 (Phelan-McDermid syndrome) is a genetic condition; lifestyle habits do not cause it, but they can shape symptom control, day-to-day function, and long‑term complications. Understanding how lifestyle affects Monosomy 22q13.3 helps families prioritize supports that improve feeding, sleep, movement, and communication. The elements below focus on routines and choices that can make symptoms easier to manage and quality of life better.
Tailoring food textures and pacing meals can reduce choking and aspiration in children with swallowing difficulty. Consistent feeding strategies may lower reflux and respiratory complications.
Ensuring adequate calories and protein supports growth and muscle strength despite hypotonia. Attention to micronutrients (like vitamin D and calcium) may help bone health when mobility is limited.
Ample fluids and fiber can ease constipation, a common issue that worsens discomfort and behavior. Regular bowel routines may reduce abdominal pain that interferes with therapies and learning.
Daily assisted movement and physiotherapy can improve muscle tone, balance, and endurance in hypotonia. Better mobility may enhance participation in school, play, and self-care.
Risk prevention
Monosomy 22q13.3 is a genetic condition, so you can’t prevent the chromosome change itself, but you can lower the chance of complications and support development early. Prevention is about lowering risk, not eliminating it completely. Recognizing early symptoms of Monosomy 22q13.3—like low muscle tone, feeding challenges, or delayed speech—can prompt early therapies that make a real difference. Work with your care team to create a plan that fits your child’s needs and your family’s routine.
Keep routine vaccines up to date to reduce serious infections that can hit harder in kids with low muscle tone. Ask about additional flu and pneumonia protection based on your child’s health.
Start physical, occupational, and speech or communication therapy as soon as concerns appear. Early practice builds skills and prevents secondary problems like joint stiffness or poor balance.
Learn seizure signs and have a clear rescue plan if seizures occur. Regular follow-up can fine-tune medicines and lower emergency visits.
Address reflux, constipation, or feeding difficulties early to support growth. A dietitian and feeding therapist can help reduce choking risk and ensure enough calories.
Transmission
Monosomy 22q13.3 is a genetic condition caused by a missing piece of chromosome 22; it is not an infection and cannot be caught or spread through contact, air, or food. In most families, it happens for the first time as a new change in the egg or sperm or very soon after conception.
Sometimes it can be inherited when a parent carries a balanced chromosome rearrangement—a swap of pieces that doesn’t affect the parent’s health—but can lead to a child having a missing piece. Rarely, a parent has mosaicism (the change in only some cells), which can also raise the chance of having another child with the condition. A genetics professional can explain how Monosomy 22q13.3 is inherited in your family and discuss the genetic transmission of Monosomy 22q13.3, including recurrence risks and options for future pregnancies.
When to test your genes
Monosomy 22q13.3 is a genetic condition; consider genetic testing at diagnosis or if there are unexplained developmental delays, low muscle tone, feeding issues, or autism features. Testing also helps guide therapies, surveillance, and family planning. If a family member is affected or a pregnancy shows concerning ultrasound findings, ask about testing.
Diagnosis
Doctors usually suspect Monosomy 22q13.3 when a child has a pattern of developmental delays, very limited speech, low muscle tone, and certain physical traits, then confirm it with genetic tests. Getting a diagnosis is often a turning point toward answers and support. The genetic diagnosis of Monosomy 22q13.3 typically involves a stepwise approach that starts broadly and becomes more targeted based on results and family history.
Providers look for global developmental delay, very limited or absent speech, low muscle tone, and autism-like behaviors. Physical traits such as larger hands, full cheeks, or decreased pain sensitivity can raise suspicion.
Standardized assessments of speech, motor, and learning skills document delays and guide therapies. These results support concern for Monosomy 22q13.3 but are not specific on their own.
This first-line genetic test can detect a missing segment on 22q13.3. It also estimates the deletion size and which genes are involved.
If microarray is normal but suspicion remains, sequencing or deletion/duplication analysis of SHANK3 can find smaller changes. This can confirm Monosomy 22q13.3 when only this gene is affected.
Stages of Monosomy 22q13.3
Monosomy 22q13.3 does not have defined progression stages. It’s a lifelong neurodevelopmental condition where abilities and medical needs can change over time and differ from person to person, rather than following predictable steps of worsening. Doctors diagnose it by reviewing development and behavior, doing a physical and neurological exam, and confirming with genetic testing such as chromosomal microarray or targeted tests; early symptoms of Monosomy 22q13.3 often include low muscle tone and delayed or limited speech. Genetic testing may be offered to clarify certain risks.
Outlook and prognosis
Looking ahead can feel daunting, but most children with Monosomy 22q13.3 make progress over time, especially when therapies start early. Daily routines often adapt—speech therapy, occupational therapy, and extra support at school can help kids build communication, motor, and self‑care skills. Doctors call this the prognosis—a medical word for likely outcomes. Some children will use a few words or a communication device, while others communicate mainly through gestures and behavior; the range is wide and can shift with age and support.
Serious, life‑shortening complications are uncommon in Monosomy 22q13.3, and many people live into adulthood. When medical issues occur, they often relate to seizures, low muscle tone, feeding difficulties, or breathing and heart concerns; careful monitoring usually helps manage these. Early symptoms of Monosomy 22q13.3 that influence outlook can include delayed speech, low muscle tone, and developmental delays, which is why early evaluation and care matter. In medical terms, the long-term outlook is often shaped by both genetics and lifestyle.
Everyone’s journey looks a little different. With ongoing care, many people maintain steady gains in mobility, communication, and learning, though progress may be gradual. The future may look uncertain now, but coordinated care—developmental therapies, seizure management if needed, nutrition support, and behavior strategies—tends to improve quality of life. Talk with your doctor about what your personal outlook might look like.
Long-term effects
Monosomy 22q13.3 has lifelong effects that usually center on development, communication, behavior, and several body systems. Long-term effects vary widely, and strengths and challenges can look different from one person to the next. Many families recall early symptoms of Monosomy 22q13.3 such as low muscle tone and feeding difficulties, which may evolve into ongoing differences in speech, learning, and sensory processing. Over time, needs can change from childhood into adulthood as learning, movement, and health patterns settle into a long-term rhythm.
Spoken words may remain limited or absent. Understanding of language is often stronger than the ability to speak.
Learning typically progresses slowly across childhood and adulthood. Most people with Monosomy 22q13.3 continue to build skills but at a different pace.
Low muscle tone and coordination challenges can persist. Balance, endurance, and fine motor control may remain weaker than peers.
Many have social communication differences and repetitive behaviors. Sensory sensitivities to sound, touch, or light are common.
How is it to live with Monosomy 22q13.3?
Living with monosomy 22q13.3 (also known as Phelan‑McDermid syndrome) often means navigating global developmental delays, limited or absent speech, low muscle tone, and sensory differences that can affect learning, communication, and daily routines. Many families build structured days with visual supports, therapies, and adaptive equipment to help with mobility, feeding, sleep, and behavior, while also coordinating frequent medical visits for issues like seizures, gastrointestinal problems, or recurrent infections. Caregivers and siblings may feel both joy and fatigue as they balance advocacy, appointments, and everyday life, so practical respite, school-based services, and community support can make a real difference. With early therapies and a consistent care team, many children and adults gain new skills over time and participate meaningfully in home and community activities.
Treatment and drugs
Treatment for Monosomy 22q13.3 focuses on easing symptoms, building skills, and preventing complications, since there’s no cure yet. Care usually includes early intervention with speech, occupational, and physical therapy; many children benefit from augmentative and alternative communication tools to support limited or absent speech. Doctors sometimes recommend a combination of lifestyle changes and drugs, such as medicines for seizures, sleep problems, reflux, constipation, or behavioral symptoms, along with nutrition support and feeding therapy when growth is a concern. For many, coordinated care with neurology, genetics, gastroenterology, rehabilitation, and mental health services helps tailor support across childhood and adulthood; hearing, vision, heart, and kidney checks are guided by individual needs. Supportive care can make a real difference in how you feel day to day, and regular follow-up helps adjust therapies as abilities and health needs change.
Non-drug treatment
Daily life often revolves around therapies that build communication, movement, and everyday skills. Non-drug treatments often lay the foundation for progress at home, school, and in the community. Many early symptoms of Monosomy 22q13.3—like low muscle tone, feeding challenges, and speech delays—respond best to structured, hands-on support. Plans are tailored and adjusted over time to match changing needs and goals.
Home- and clinic-based services in infancy and toddler years target communication, motor skills, and feeding. Coordinated, frequent practice can accelerate developmental gains.
Speech-language therapy focuses on understanding language and using it to communicate. Augmentative and alternative communication—like picture boards, tablets, or eye-gaze devices—can give many with Monosomy 22q13.3 a reliable voice.
Targeted exercises build strength, balance, and coordination affected by low muscle tone. Therapists teach safe movement patterns and play-based activities to support walking and endurance.
Training builds hand skills, self-care, and attention for daily routines. Therapists also adapt seating, utensils, and toys to make tasks easier and safer for people with Monosomy 22q13.3.
Your genes may have an impact on how drugs work for you
Even when two people share Monosomy 22q13.3, small DNA differences can change how their bodies absorb, break down, and respond to medications. Pharmacogenetic testing can sometimes guide choices and dosing, but clinicians still tailor treatment through careful monitoring.
Pharmacological treatments
Monosomy 22q13.3, also known as Phelan-McDermid syndrome, doesn’t have a single curative medicine. Treatments focus on easing day-to-day issues like seizures, sleep disruption, reflux, constipation, irritability, and anxiety. Not everyone responds to the same medication in the same way. Early symptoms of Monosomy 22q13.3 like frequent waking or reflux often guide which treatments doctors try first.
Levetiracetam, valproate, lamotrigine, or topiramate are commonly used to prevent seizures. Doctors choose based on seizure type and side‑effect profile.
Diazepam nasal spray or rectal gel, or intranasal midazolam, can stop a prolonged seizure. Caregivers are often taught when and how to give them.
Melatonin at bedtime is often tried first for delayed sleep or frequent waking. Some may benefit from clonidine or guanfacine at night if melatonin alone isn’t enough.
Risperidone or aripiprazole may ease severe irritability or aggression, especially when behaviors resemble autism‑related irritability seen in Monosomy 22q13.3. Weight, glucose, and movement effects are monitored.
Genetic influences
In Monosomy 22q13.3, a small piece from the tip of chromosome 22 is missing, leaving just one working copy of several genes; loss of a key gene called SHANK3 likely explains many features. This usually happens as a new change around conception and isn’t caused by anything done during pregnancy. In some families, the deletion comes from a parent who carries a balanced chromosome change without symptoms, which raises the chance it could happen again. When no parent carries such a change, the chance of it happening in another pregnancy is generally low. The size and exact position of the missing piece vary, and that can shape how the condition looks from one person to the next. Understanding whether a condition is inherited can guide next steps. Genetic testing for Monosomy 22q13.3 can confirm the missing segment and clarify family risks so you and your care team can plan supports early.
Is Monosomy 22q13.3 genetic?
Genetics is central in Monosomy 22q13.3: it results from missing genetic material at the end of chromosome 22. Most cases are de novo, though some come from a balanced parental rearrangement. Genetic testing clarifies the deletion size, inheritance risk, and family planning.
Pharmacogenetics—how genetics influence drug effects
For Monosomy 22q13.3, day-to-day care often relies on medicines for seizures, sleep, irritability, anxiety, or constipation, and genes can shape how well these drugs work and which dose is safest. Many commonly used options—such as certain antidepressants, antipsychotics for irritability, and some seizure medicines—are broken down by liver enzymes that vary from person to person. A “slow metabolizer” may process medicine more slowly, leading to higher levels and more side effects, while a “fast metabolizer” may clear it too quickly to help. Pharmacogenetic testing can guide choices for drugs like risperidone or some SSRIs, and for seizure medicines where known gene risks exist, including rare but serious skin reactions with carbamazepine or phenytoin in people who carry specific immune-system markers. It can also flag when codeine or tramadol may not work as expected, or could cause side effects, because the body converts them at different speeds. These drug–gene insights don’t replace clinical judgment—age, other health conditions, and multiple medicines also matter—but pharmacogenetic testing in Monosomy 22q13.3 can reduce trial-and-error and help tailor treatment more safely.
Interactions with other conditions
Monosomy 22q13.3 often occurs alongside other health issues that shape day-to-day care, such as autism features, epilepsy, gastrointestinal reflux, constipation, and sleep problems. Doctors call it a “comorbidity” when two conditions occur together. When autism is also present, communication and behavioral therapies used for autism can support learning and reduce frustration for people with Monosomy 22q13.3. If epilepsy is part of the picture, fevers and common infections may lower the seizure threshold, so prompt treatment of illness and a coordinated seizure plan are important. Low muscle tone can make reflux and swallowing difficulties worse, which in turn can raise the risk of chest infections and complicate feeding; sleep apnea can also interact with low tone and nasal congestion. Kidney or lymphatic differences reported in some people with Monosomy 22q13.3 may influence fluid balance and how certain medicines are cleared, so sharing all diagnoses with each specialist helps tailor safe, effective 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.
History
Throughout history, people have described infants who were slow to develop speech, had low muscle tone, and faced feeding challenges, yet the exact cause wasn’t clear. Families sometimes noticed that similar features appeared in more than one child, but without modern tools there was no way to see the tiny missing piece on the tip of chromosome 22 that we now associate with Monosomy 22q13.3.
First described in the medical literature as a small deletion at the end of chromosome 22, the condition gradually became clearer as laboratory methods improved. In the 1980s and 1990s, techniques like high‑resolution chromosome studies and FISH testing allowed clinicians to detect subtelomeric deletions that standard karyotypes missed. Early reports focused on shared features—limited speech, low muscle tone, and developmental delays—while later work connected these features to the specific missing region at 22q13.3.
From these first observations, researchers began to recognize that the size of the missing segment could vary from person to person. This helped explain why some people with Monosomy 22q13.3 had more medical needs than others, and why early symptoms of Monosomy 22q13.3 were sometimes subtle in infancy but clearer over time. As medical science evolved, dedicated registries and family networks brought together clinical notes and lived experience, giving a fuller picture of behavior, growth, and health across childhood and adulthood.
In recent decades, awareness has grown as newer genetic tools—like chromosomal microarray and sequencing—have made testing more accurate and more widely available. These methods can pinpoint the exact breakpoints and genes involved, including the critical role of the SHANK3 gene for many individuals, and they also identify people with very small deletions who might previously have gone undiagnosed. With this, the condition moved from being considered very rare to more readily recognized in genetics clinics and developmental programs.
Over time, the way the condition has been understood has changed, but the goal has remained the same: to identify Monosomy 22q13.3 earlier and connect people with targeted therapies and supports. Today’s understanding reflects both careful clinical description and advances in genetic testing. Looking back helps explain why some adults are only now receiving a diagnosis, and it underscores how continued research and family advocacy have shaped the care people receive now.