[Phenotype variability in Noonan syndrome patients with and without PTPN11 mutation]

Noonan syndrome-causing genes: Molecular update and an assessment of the mutation rate

Noonan syndrome is a common autosomal dominant disorder characterized by short stature, congenital heart disease and facial dysmorphia with an incidence of 1/1000 to 2500 live births. Up to now, several genes have been proven to be involved in the disturbance of the transduction signal through the RAS-MAP Kinase pathway and the manifestation of Noonan syndrome. The first gene described was PTPN11, followed by SOS1, RAF1, KRAS, BRAF, NRAS, MAP2K1, and RIT1, and recently SOS2, LZTR1, and A2ML1, among others. Progressively, the physiopathology and molecular etiology of most signs of Noonan syndrome have been demonstrated, and inheritance patterns as well as genetic counseling have been established. In this review, we summarize the data concerning clinical features frequently observed in Noonan syndrome, and then, we describe the molecular etiology as well as the physiopathology of most Noonan syndrome-causing genes. In the second part of this review, we assess the mutational rate of Noonan syndrome-causing genes reported up to now in most screening studies. This review should give clinicians as well as geneticists a full view of the molecular aspects of Noonan syndrome and the authentic prevalence of the mutational events of its causing-genes. It will also facilitate laying the groundwork for future molecular diagnosis research, and the development of novel treatment strategies.

Cardiovascular disease in Noonan syndrome

BACKGROUND

Noonan syndrome (NS), a relatively common autosomal dominant disorder with an incidence of 1 in 1000 to 2500 live births, is the most common syndromic cause of congenital heart disease after Trisomy 21.

OBJECTIVE

To comprehensively define the spectrum of cardiac morphology and specific clinical course of a large cohort of NS patients.

DESIGN

Retrospective, descriptive case series study.

PATIENTS

An international Harvard-based NS registry was combined with clinical data from NS patients followed at Boston Children's Hospital, Massachusetts, USA.

RESULTS

We identified 293 patients with NS. Cardiovascular disease was seen in 81% (n=237) including pulmonary stenosis in 57%, secundum atrial septal defects in 32% and hypertrophic cardiomyopathy in 16%. A genetic mutation of the RAS-MAPK signalling pathway was identified in 62% (n=136). Genotype-phenotype associations were noted between PTPN11 mutations and atrial septal defects (p=0.001), and pulmonary stenosis (p<0.001). RAF1 mutations were associated with hypertrophic cardiomyopathy (p<0.001). Cardiovascular outcomes that differed specifically in a NS cohort included high re-intervention rates (65%) after percutaneous balloon pulmonary valvuloplasty for valvar pulmonary stenosis. Additionally, in NS patients with hypertrophic cardiomyopathy, a clinically significant regression of hypertrophy (17%) was observed as was a markedly higher incidence of concomitant congenital heart defects (70%).

CONCLUSIONS

Patients with NS have a distinct spectrum of cardiac phenotypes that may have a natural history and response to therapy atypical to that normally seen in non-syndromic heart disease. A diagnosis of NS in a patient with pulmonary stenosis or infant-onset hypertrophic cardiomyopathy would facilitate condition-specific counselling on outcome and prognosis.

Phenotypic spectrum of 80 Greek patients referred as Noonan syndrome and PTPN11 mutation analysis: the value of initial clinical assessment

Noonan syndrome (NS) is a common multiple congenital anomaly entity, the diagnosis of which, on clinical grounds, is based on a comprehensive scoring system in order to select patients for molecular confirmation. Our aim was to evaluate the phenotypic characteristics in the light of PTPN11 mutations. The study revealed 80 patients who were referred with initial indication of NS or Noonan-like syndrome (NLS) and further assessed by a clinical geneticist; 60/80 index patients, mean age 5.9 ± 5.3 years, fulfilled the NS criteria. Molecular analysis of PTPN11 gene (exons and their flanking regions) of the total population revealed mutations in 17/80 patients, all belonging in the group of the patients screened with the scoring system. All mutations were heterozygous missense changes, mostly clustering in exon 3 (8/17), followed by exons 13 (3/17), 8 (2/17), 7 (2/17), 2 (1/17) and 4 (1/17). We conclude that (a) most of our clinically diagnosed NS cases were sporadic (b) PTPN11 analysis should be limited to those fulfilling the relevant NS criteria (c) Cardiovascular evaluation should comprise all NS patients, while pulmonary stenosis, short stature, and thorax deformities prevailed among those with PTPN11 mutations.

Analysis of the PTPN11 gene in idiopathic short stature children and Noonan syndrome patients

BACKGROUND

Mutations in the PTPN11 gene are the main cause of Noonan syndrome (NS). The presence of some NS features is a frequent finding in children with idiopathic short stature (ISS). These children can represent the milder end of the NS clinical spectrum and PTPN11 is a good candidate for involvement in the pathogenesis of ISS.

OBJECTIVE

To evaluate the presence of mutations in PTPN11 in ISS children who presented NS-related signs and in well-characterized NS patients.

PATIENTS AND METHODS

We studied 50 ISS children who presented at least two NS-associated signs but did not fulfil the criteria for NS diagnosis. Forty-nine NS patients diagnosed by the criteria of van der Burgt et al. were used to assess the adequacy of these criteria to select patients for PTPN11 mutation screening. The coding region of PTPN11 was amplified by polymerase chain reaction (PCR), followed by direct sequencing.

RESULTS

No mutations or polymorphisms were found in the coding region of the PTPN11 gene in ISS children. Nineteen of the 49 NS patients (39%) presented mutations in PTPN11. No single characteristic enabled us to distinguish between NS patients with or without PTPN11 mutations.

CONCLUSION

Considering that no mutations were found in the present cohort with NS-related signs, it is unlikely that mutations would be found in unselected ISS children. The van der Burgt et al. criteria are adequate in attaining NS diagnosis and selecting patients for molecular studies. Mutations in the PTPN11 gene are commonly involved in the pathogenesis of NS but are not a common cause of ISS.