The aim of this retrospective observational study is to investigate the association between genotype and craniofacial phenotype in orthodontic patients affected by Marfan and Loeys-Dietz syndromes. A total of 39 patients aged between 4 and 18 years were enrolled and stratified into four groups according to the underlying pathogenic genetic variants. Lateral cephalometric radiographs were analyzed to assess sagittal, vertical, and cranial base skeletal relationships. Each patient group was compared with age- and sex-matched controls, as well as between syndromes and among Marfan subgroups. Statistical analyses were performed to evaluate differences in craniofacial parameters and to explore potential genotype-phenotype correlations relevant for orthodontic diagnosis.

This retrospective observational study aims to investigate the association between genotype and craniofacial phenotypic variation in orthodontic patients affected by Marfan syndrome (MFS) and Loeys-Dietz syndrome (LDS). Patients aged between 4 and 18 years who referred to the Unit of Orthodontics and Paediatric Dentistry and had a confirmed genetic diagnosis were considered eligible for inclusion. Parents or legal guardians provided informed consent prior to data collection.

A total of 39 patients were enrolled and divided into four groups according to the underlying pathogenic genetic variant:

• Group FBN1Cys: Marfan patients with missense cysteine variants of the FBN1 gene.
• Group FBN1m: Marfan patients with missense non-cysteine variants of the FBN1 gene.
• Group FBN1tp: Marfan patients with truncating FBN1 variants (nonsense, frameshift or splicing mutations).
• Group LD: Patients with Loeys-Dietz syndrome carrying pathogenic variants in TGFBR1 or TGFBR2 genes.

An age- and sex-matched control group without genetic disorders and without previous orthodontic treatment was selected for each study group. All patients underwent orthodontic diagnostic records including lateral cephalometric radiographs. Due to the retrospective nature of the study and the use of different radiographic units, only angular cephalometric measurements were considered.

Cephalometric analysis was performed using dedicated software according to Giannì's method, evaluating sagittal, vertical and cranial base relationships. Each patient was compared with the corresponding control group, between MFS and LDS patients, and among the Marfan subgroups. All measurements were performed by a single operator and intra-rater reliability was assessed.

Sample size was defined by the availability of patients affected by these rare genetic disorders who met the inclusion criteria during the study period. Descriptive statistics were calculated for all cephalometric parameters. Shapiro-Wilk test was applied to assess data normality. Differences between groups were evaluated using ANOVA, followed by Tukey's post-hoc test when appropriate.

Statistical analysis was conducted using R software, with significance for all tests predetermined at p < 0.05.

Inclusion Criteria:

• Diagnosis of Marfan/Loeys-Dietz syndrome;
• formal request of parents or legal guardians for orthodontic evaluation;
• aged between 4 and 18;
• no previous orthopaedic or orthodontic treatment.

Exclusion Criteria:

• History of craniofacial anomalies (e.g., cleft lip/palate, craniosynostosis) or syndromic conditions other than Marfan/Loeys-Dietz syndrome;
• previous orthopaedic or orthodontic treatment;
• poor quality cephalograms.

Patients referring for orthodontic consultation from the Unit Centre for Inherited Cardiovascular Diseases, IRCCS Foundation, University Hospital Policlinico San Matteo, Pavia, Italy

Data will be available upon motivated request to the Principal Investigator.