Apert Syndrome

Apert syndrome (acrocephalosyndactyly type I) is one of the most recognisable craniosynostosis syndromes and the one with the most severe hand involvement.

• Genetics: Autosomal dominant. Caused by FGFR2 (Fibroblast Growth Factor Receptor 2) mutations.
• Birth prevalence: Roughly 1 in 65,000-80,000 live births.
• New mutations: Almost all cases arise as new (de novo) mutations; there is a strong paternal age effect.
• The orthopaedic angle: Apert is the syndrome where the hand surgeon plays a central role. The complex (bony) syndactyly is more severe than in any other common craniosynostosis syndrome.

FGFR2 gain-of-function

According to PubMed, Wilkie and colleagues showed that essentially all Apert cases result from one of two adjacent missense mutations in FGFR2: Ser252Trp or Pro253Arg (Wilkie, Nat Genet 1995). These sit in the linker between the second and third immunoglobulin-like domains of the receptor.

• FGFR signalling normally coordinates suture and limb morphogenesis.
• The Apert mutations cause a gain of function - enhanced ligand binding and prolonged signalling.
• The result is premature fusion of cranial sutures (craniosynostosis) and abnormal fusion of the developing digital rays (syndactyly).

Allelic with Crouzon

Apert is allelic with Crouzon syndrome: both are caused by FGFR2 mutations, but Crouzon mutations affect the third Ig domain and produce craniosynostosis with normal limbs, whereas the Apert linker mutations produce craniosynostosis plus severe syndactyly (Wilkie, Nat Genet 1995).

Genotype-phenotype correlation

• The Ser252Trp mutation tends to produce more severe craniofacial disease (more cleft palate).
• The Pro253Arg mutation tends to produce more severe syndactyly of the hands and feet (Wilkie, Novartis Found Symp 2001).

Why almost every case is new and paternally derived

The overview notes that Apert is "almost always a new (de novo) mutation with a strong paternal age effect" - but the reason is never explained, and it is a high-yield genetics point. Apert is the textbook example of a "paternal age effect" disorder driven by selfish spermatogonial selection.

• The two recurrent FGFR2 mutations arise as new mutations on the paternally derived allele in essentially all cases - they occur during spermatogenesis, not oogenesis.
• These specific gain-of-function mutations give the mutant spermatogonial stem cell a selective growth/clonal advantage in the testis, so mutant clones expand and accumulate with the man's age ("selfish" selection, analogous to a benign tumour of spermatogonia).
• The result is that the risk rises with advancing paternal age, the mutation is paternal in origin, and the small number of mutable nucleotides explains why the same two substitutions recur across unrelated families.

This is why the recurrence risk for unaffected parents is very low (a sporadic de novo event), whereas an affected individual transmits it as autosomal dominant with a 50% risk - the distinction families need for counselling.

The classification box flags "elbow and shoulder stiffness", the clinical exam says to "check elbow and shoulder range (often reduced)", and the complications list "reduced elbow/shoulder motion - proximal joint involvement" - but the topic never explains why. The Apert upper limb is abnormal proximally as well as distally: there is progressive synostosis and dysplasia of the elbow and shoulder, and it compounds the hand disability.

• Elbow - the hallmark is humeroradial (radiohumeral) synostosis: the radius and capitellum progressively fuse, so the elbow loses flexion-extension and, with it, the ability to bring the hand to the mouth and midline. (This is distinct from proximal radioulnar synostosis, which limits forearm rotation and is covered in its own topic.)
• Shoulder - glenohumeral dysplasia with a small, abnormally shaped glenoid/proximal humerus and progressive loss of abduction and elevation.
• Progressive - like the cranial sutures and the cervical spine, these joints are often mobile in infancy and stiffen with growth, so range of motion documented early may not last.

Why it matters:

The clinical lesson is that the disability is a whole-limb problem: a technically excellent hand reconstruction can be undermined if the child cannot position the hand because the elbow and shoulder are stiff, so the proximal joints must be assessed and the family counselled accordingly. Surgery to the proximal joints is uncommon; therapy and adaptive strategies dominate.

Other FGFR-related craniosynostosis syndromes:

Key Distinguishing Points:

• Apert: The most severe hand syndactyly (bony fusion, conjoined nail).
• Crouzon: FGFR2 like Apert, but limbs are normal - this is the classic contrast.
• Pfeiffer: Broad thumbs and big toes are the clue.
• Saethre-Chotzen: Milder, with ptosis and a low frontal hairline.

Surgical Complications of Hand Reconstruction

Functional and Long-Term Issues

Perioperative and Anaesthetic Considerations

Critical considerations for any surgery in Apert syndrome:

• Difficult airway: Midface hypoplasia and a high-arched/cleft palate make intubation challenging - plan ahead.
• Cervical fusion: Progressive vertebral fusion (often C5-C6) limits safe neck extension - avoid forced positioning.
• Obstructive sleep apnoea: Common; optimise and monitor in the perioperative period.
• Raised intracranial pressure: Must be excluded/treated by the craniofacial team before elective limb surgery.

Why It Matters for the Exam

Apert syndrome is the classic viva case linking genetics, craniofacial surgery and hand surgery. Examiners expect you to:

• Name the FGFR2 mutations and the link to Crouzon.
• Describe the Upton hand classification and the border-first, staged release principle.
• Explain why symphalangism caps the functional outcome.

Functional Outcomes

According to PubMed, even with expert staged reconstruction the goal is a functional, opposable hand with a rudimentary but useful pinch rather than normal fingers; symphalangism is repeatedly cited as the factor that "darkens" the functional prognosis (Salazard, Chir Main 2008). Early, specialist, staged surgery completed by 2-4 years gives the best functional and aesthetic results with acceptable revision rates (Roje, Acta Chir Plast 2012).

Counselling Families

• The hand will not look or move normally, but most children achieve independent grasp and pinch.
• Multiple operations are expected; this is a planned, staged journey, not a single fix.
• Care is lifelong and multidisciplinary (craniofacial, neurosurgery, hand, ENT, genetics, development).

Global Epidemiology

• Birth prevalence around 1 in 65,000-80,000; one of the more common craniosynostosis syndromes worldwide.
• Almost all cases are de novo FGFR2 mutations with a strong paternal age effect.
• Two recurrent mutations (Ser252Trp, Pro253Arg) account for the overwhelming majority of cases globally.

Side-by-Side Guidance

Practice Variation

• High-resource settings: Specialist craniofacial units, distraction osteogenesis, multi-stage hand reconstruction and FGFR2 testing are available.
• Limited-resource settings: Diagnosis is clinical; care prioritises airway/feeding safety and the most functionally important hand release (thumb and first web) where full multi-stage programmes are not feasible.
• Family support organisations (craniofacial and Apert-specific groups) are valuable everywhere for psychosocial support and shared decision-making.

Timing and number of hand operations There is no single agreed protocol. Most centres favour an early, border-first, staged release completed by 2-4 years, but the exact age to start, the number of stages, and how aggressively to pursue a five-fingered hand in type III cases vary between units (Roje 2012; Theman/Upton 2018).

How far to go in the type III hand Central coalition osteotomy can create five digits in severe hands, but it requires more operations. Whether the extra aesthetic and functional gain justifies the additional surgery is a judgement made with each family (Theman/Upton 2018).

Feet Toe syndactyly is usually left alone because it rarely impairs function; routine separation is not recommended, and indications for foot surgery remain selective.

Genotype-guided counselling The Ser252Trp/Pro253Arg phenotype gradient (worse face vs worse hands) is real but not absolute, so genotype informs but does not dictate individual prognosis (Wilkie 2001).