Building Your Care Team
There are no HCS clinics. There is no published multidisciplinary care guideline. What exists is a pattern from the literature: the patients who do best are the ones who assemble a coordinated team across multiple specialties and make sure those specialists actually talk to each other. Here are the roles you shoulddd consider getting covered — and why each one matters for HCS specifically.
Endocrinologist
Your quarterback for bone health. Manages bisphosphonates, denosumab, or romosozumab. Orders and interprets DEXA scans. Monitors bone turnover markers (CTX, P1NP). In children, coordinates with pediatric endocrinology for growth tracking.In Alberta, for me anyway, I have a Rheumatologist who manages these things for me.
Neurosurgeon / Neurologist
Basilar invagination and Chiari malformation occur in roughly half of HCS patients and can be life-threatening. Needs to be monitoring with periodic imaging even if you're asymptomatic. Urgent if any neurological symptoms develop.
Cardiologist
Congenital heart defects (patent ductus arteriosus, septal defects) and valve disease (mitral regurgitation, aortic stenosis) are documented in HCS though it only occurs sometimes in some children. One patient required mitral valve replacement at age 14 and a pacemaker at 18. Echocardiographic monitoring may be essential.
Nephrologist
Polycystic kidney disease appears in an estimated 10% of HCS patients and has progressed to end-stage renal failure in documented cases. Renal ultrasound at diagnosis and periodic monitoring are critical — especially since HCS and serpentine fibula-polycystic kidney syndrome are now considered the same condition.
Dental Specialist
HCS causes progressive alveolar bone atrophy, severe periodontal disease, and premature tooth loss. The literature recommends preserving tooth structure and avoiding invasive procedures where possible — especially if you're on bisphosphonates, which carry jaw osteonecrosis risk.
Audiologist
Hearing loss — both sensorineural and conductive — is a recognized feature of HCS. Progressive loss has been documented in multiple cases. Annual audiometry catches changes early enough for hearing aid fitting or other intervention.
Respirologist / Pulmonologist
Thoracic deformities cause restrictive lung disease. Recurrent respiratory infections are common. In severe cases, basilar invagination can cause central respiratory arrest. Vocal cord paralysis has also been documented. If you have any spinal or thoracic involvement, pulmonary function testing matters.
Clinical Geneticist / Genetic Counselor
Confirms diagnosis via NOTCH2 exon 34 sequencing. Essential for family planning discussions, explaining autosomal dominant inheritance to family members, and coordinating preimplantation genetic testing (PGT-M) if desired.
No single specialist can manage HCS alone. The challenge is coordination — making sure your cardiologist knows what your endocrinologist is prescribing, and your dentist knows you're on bisphosphonates before they plan any procedure. Print your medication list and bring it to every appointment. It sounds basic. It's the most protective thing you can do.
Monitoring Schedule
There is no published surveillance protocol for HCS. The schedule below is derived from the clinical literature, case report recommendations, and the pattern of complications documented across the fewer than 100 known cases worldwide. Discuss it with your care team — your specific needs may be different depending on which systems are affected.
DEXA Bone Density Scan
Quantifies osteoporosis severity, tracks treatment response
Bone Turnover Markers (CTX, P1NP)
Tracks osteoclast activity and treatment response between DEXA scans
Hand & Foot X-rays
Documents acro-osteolysis progression — the one thing no treatment currently stops
Skull Base CT or MRI
Screens for basilar invagination and Chiari malformation — occurs in ~50% of patients
Spine X-ray Series
Compression fractures, kyphosis, scoliosis progression, cervical instability
Echocardiogram
Valvular disease, congenital defects (PDA, VSD/ASD), myxomatous degeneration
Renal Ultrasound + Function Panel
Polycystic kidneys in ~10% of patients; has caused end-stage renal failure in documented cases
Audiometry
Progressive sensorineural and/or conductive hearing loss
Pulmonary Function Tests
Restrictive lung disease from thoracic deformities; baseline before any surgery
Dental Exam with Panoramic X-ray
Alveolar bone atrophy, periodontal disease, impacted/supernumerary teeth, root resorption
Keep a binder. With fewer than 100 known cases, most specialists you see will be encountering HCS for the first time. Having your imaging history, DEXA trends, genetic report, and medication list organized in one place saves everyone time and prevents mistakes.
Emergency Red Flags
Some HCS complications are slowly progressive. Others aren't. Basilar invagination and cardiac events have caused sudden death in documented cases. These are the signs that mean you need emergency evaluation — not your next scheduled appointment.
- Severe sudden headache with neck stiffness, vomiting, or vision changes — may indicate hydrocephalus from basilar invagination
- New weakness, numbness, or coordination loss in arms or legs — spinal cord compression from basilar invagination or vertebral collapse
- Difficulty swallowing or breathing that worsens rapidly — upper airway obstruction or brainstem compression; vocal cord paralysis is documented
- Sleep apnea that suddenly worsens or irregular breathing during sleep — central respiratory arrest from basilar invagination is a documented cause of death
- Chest pain, palpitations, or fainting — cardiac valve disease can worsen unpredictably; heart block has required emergency pacemaker placement
- Blood in urine or severe flank pain — may signal renal cyst complication or progressive kidney disease
- New seizures — documented in HCS patients with neurological involvement; one patient developed progressive hemiplegia following seizure onset
- Sudden severe back pain with height loss — vertebral compression fracture; may require surgical stabilization in HCS due to poor bone quality
Carry a medical ID or emergency summary card. In an emergency room, the team treating you will almost certainly not know what HCS is. A card listing your condition, NOTCH2 mutation, current medications, airway concerns (difficult intubation — see Surgery section below), and your specialist contacts can be the difference between safe treatment and a dangerous mistake.
Surgical & Anesthesia Safety
HCS is classified in anesthesia literature as one of the most difficult airway-related syndromes. If you need surgery — for any reason, not just HCS-related — this section explains what your surgical team needs to know. Print it. Bring it. Don't assume they've seen this before, because they almost certainly haven't.
Airway Challenges — Why Intubation Is Dangerous
Micrognathia (small jaw), abnormal dentition, short neck, mandibular hypoplasia, and cervical spine deformities combine to create a textbook difficult airway. Published anesthesia case reports recommend video laryngoscopy or fibreoptic intubation rather than standard direct laryngoscopy. Smaller-size endotracheal tubes are typically required.
One published case used fibreoptic nasotracheal intubation for dental surgery, but noted that skull base fragility creates a risk of fracture during nasotracheal approaches — preoperative CT of the skull base was performed first to rule out existing fractures.
Cervical spine instability means neck extension during intubation is dangerous. The anesthesiologist needs to know this before the patient is on the table.
Bleeding Risk & Coagulation
NOTCH2 mutations are associated with bleeding risks. The anesthesia literature recommends preoperative coagulation profile assessment and ensuring adequate blood products are available before any procedure. This isn't theoretical — it's a specific recommendation from published HCS surgical case studies.
Positioning & Fracture Prevention
Severe osteoporosis and joint laxity mean that positioning during surgery can itself cause fractures. Pressure points need extra padding. Prone positioning (face-down, used in spinal surgery) requires particular care. The surgical team needs to handle positioning gently and deliberately — no routine lifting or turning.
Spinal Surgery — Why HCS Makes It Harder
Spinal surgery in HCS is documented as exceptionally challenging. Distorted anatomy from persistent open sutures, reduced bone strength making screw fixation unreliable, and the risk of osteolysis causing fusion failure are all documented complications. One case of basilar invagination repair required a novel cranial vault suspension technique because standard approaches failed — with a 9.5-year follow-up confirming long-term stability.
If spinal surgery is being considered, the surgeon needs to be someone who has experience with severe osteoporosis cases — ideally at an academic center with craniocervical expertise.
Respiratory Considerations During Surgery
HCS patients may have severe restrictive lung disease from thoracic deformities, kyphoscoliosis, and chest wall abnormalities. Mechanical ventilation settings need to account for this. Pulmonary function testing before any planned surgery gives the anesthesia team the data they need to ventilate safely.
The published anesthesia case reports for HCS explicitly recommend: video laryngoscope or fibreoptic scope for intubation, smaller endotracheal tubes, preoperative coagulation profiles, gentle positioning with pressure-point padding, and available blood products. Share these recommendations with your surgical team before the procedure, not the morning of.
Dental Management — The Bisphosphonate Paradox
HCS attacks your teeth from below. The alveolar bone — the ridge of bone that holds teeth in place — progressively atrophies, causing severe periodontal disease and premature tooth loss. Published cases describe generalized alveolar bone destruction, root resorption of multiple teeth, impacted teeth, and even supernumerary teeth.
Here's the paradox: the most commonly prescribed medications for HCS osteoporosis — bisphosphonates — carry a known risk of osteonecrosis of the jaw (ONJ), a condition where jawbone tissue dies after dental procedures. The very medication protecting your spine and hips creates additional risk for your mouth.
What the Literature Recommends
Preserve — Don't Extract
The literature explicitly recommends avoiding invasive dental procedures where possible. Tooth structure should be preserved because the alveolar bone resorption may continue regardless — pulling a tooth doesn't stop the underlying process, and the gap left behind accelerates further bone loss. Conservative restorations are preferred over extractions.
Bisphosphonate-Jaw Risk Coordination
If you're on bisphosphonates (zoledronic acid, alendronate, pamidronate), your dentist must know before any invasive procedure. Bisphosphonate-related osteonecrosis of the jaw (BRONJ) is a recognized complication. If surgery is unavoidable, timing relative to bisphosphonate dosing matters — this is a conversation between your endocrinologist and your oral surgeon, not something to figure out in the dental chair.
Frequent Monitoring Protocol
Dental exams every six months with panoramic X-rays to track alveolar bone levels, identify root resorption early, and catch impacted teeth before they cause problems. Aggressive preventive care — professional cleanings, fluoride, meticulous home hygiene — is the best defense against the periodontal disease that HCS accelerates.
Beyond Bones — Heart, Kidneys & Lungs
HCS is primarily known for its skeletal effects, but NOTCH2 signaling is involved in the development of the heart, kidneys, and other organs. The extraskeletal complications are less discussed but can be just as serious.
Cardiovascular Complications
Documented cardiac findings in HCS include patent ductus arteriosus, atrial and ventricular septal defects, and mitral and aortic valve abnormalities. The valve disease can be progressive — one well-documented case showed myxomatous degeneration of the mitral valve requiring replacement at 14, heart block requiring a pacemaker at 18, and worsening aortic stenosis requiring valve replacement at 20.
This doesn't mean every HCS patient will develop severe cardiac disease. It means baseline echocardiography and periodic monitoring are non-negotiable. Romosozumab (Evenity), which is one of the most promising bone treatments for HCS, carries a black-box cardiovascular warning — if you have any cardiac involvement, this needs careful discussion with both your endocrinologist and cardiologist.
Kidney Involvement — The SFPKS Connection
What used to be called serpentine fibula-polycystic kidney syndrome (SFPKS) is now recognized as the same condition as HCS — caused by the same NOTCH2 mutations. Polycystic kidneys have been documented in approximately 10% of HCS patients, with at least one case progressing to end-stage renal failure by age 14.
The exact mechanism linking NOTCH2 to kidney cyst formation isn't well understood, but the clinical reality is clear: renal ultrasound at diagnosis and annual monitoring afterward catches problems while they're still manageable. Flank pain or blood in urine warrants urgent evaluation.
Respiratory System
Three respiratory threats exist in HCS. First, thoracic deformities (kyphoscoliosis, chest wall changes) create restrictive lung disease, reducing lung capacity. Second, recurrent respiratory infections are a recognized feature. Third — and most dangerous — basilar invagination can compress the brainstem, causing Cheyne-Stokes respiration (irregular breathing patterns) and, in documented cases, central respiratory arrest.
Bilateral vocal cord paralysis has also been reported, causing upper airway obstruction. If you develop a hoarse voice, breathing difficulty, or stridor (a high-pitched sound when breathing in), this warrants ENT evaluation.
Hearing & Voice Changes
A deep, gravelly voice is one of the recognized features of HCS — distinctive enough that it's listed as a diagnostic clue. Hearing loss is more consequential. Both sensorineural loss (inner ear or nerve damage) and conductive loss (middle ear bone changes) have been documented, and in some cases the loss is progressive.
One documented case developed progressive hearing loss alongside renal failure and seizures. Bilateral sensorineural hearing loss was confirmed in a child with the related SFPKS presentation. Because hearing loss can develop gradually, annual audiometry is the only way to catch it before it significantly impacts daily life — especially in children, where undetected hearing loss affects speech and language development.
Hearing aids are the primary intervention. If you or your child is experiencing difficulty with conversations in noisy environments, turning up volumes, or asking people to repeat themselves, request an audiology referral rather than waiting for the next scheduled test.
How HCS Changes Over Time
HCS is present from birth, but it doesn't look the same at every age. The most comprehensive review of age-dependent features (Brennan & Pauli, 2001 — 57 cases) documented a clear pattern: different systems become affected at different life stages, and the condition generally worsens over time. Understanding this trajectory helps you and your care team anticipate what's coming rather than react to it after the damage is done.
The age-dependent pattern is why early diagnosis matters — not because we have a cure, but because starting bone treatment earlier, establishing baseline monitoring across all systems, and building a care team before complications develop gives you the best chance of staying ahead of the progression rather than chasing it.
Family Planning & Inheritance
HCS follows autosomal dominant inheritance. The genetics are straightforward even if the decision-making isn't. Here's what that means in practical terms.
pregnancy
If one parent has HCS, each pregnancy carries a 50% chance of the child inheriting the NOTCH2 variant and being affected. This applies equally to sons and daughters. The other 50% of pregnancies would result in a child without the condition.
However, many cases of HCS are de novo — meaning the mutation occurred spontaneously and was not inherited from either parent. If your child has HCS but neither parent does, the recurrence risk for future siblings is very low (though not zero, due to the small possibility of germline mosaicism).
There is nothing a parent did to cause the mutation. This is not caused by anything during pregnancy.
Preimplantation Genetic Testing (PGT-M)
Families who wish to have children without HCS can use preimplantation genetic testing for monogenic disorders (PGT-M). This involves creating embryos through IVF, testing each embryo for the specific NOTCH2 variant, and transferring only embryos that don't carry the mutation. A genetic counselor can walk you through the process, success rates, and costs — which vary significantly by region and healthcare system.
Prenatal testing is also available through chorionic villus sampling (CVS) or amniocentesis once a pregnancy is already established, for families who want diagnostic information during pregnancy.
A genetic counselor is your best resource here. They can explain the specifics for your family's situation, coordinate testing, and connect you with reproductive specialists experienced in PGT-M. If you don't have one on your care team yet, ask your geneticist for a referral — or contact your provincial/state genetics program directly.
For more on the NOTCH2 pathway, preclinical research, and what's being tested in the lab —
View HCS ResearchYou know more about HCS than most doctors you'll meet.
That's the reality of living with an ultra-rare condition. The knowledge you carry — about your body, your progression, your responses to treatment — is data that doesn't exist anywhere else. Share it. It matters.