From clinical suspect to molecular confirmation of noonan syndrome; contribution of “best practice” genetic counseling and new technical possibilities

Abstract

Noonan syndrome (NS) is an autosomal dominant disorder, characterized by variable expressivity of clinical features such as: postnatal growth reduction, congenital heart disease, characteristic facial dysmorphisms and development delay. In ~75% of all NS cases, germline mutations involving RAS-MAPK signaling pathway genes (PTPN11, SOS1, RAF1, KRAS, NRAS, BRAF, SHOC2, MEK1, CBL) are causative. We reported a case of 13-year-old girl [born at 36w by CS (BW 3250 g (~95?), BL 48 cm (~75?)] referred for genetic counseling due to growth retardation, facial dysmorphisms, development delay and learning disability. After birth she presented frequent vomiting, with failure to thrive and at 5 months of age underwent surgery for intestinal malrotation. Because of short stature, Growth Hormone (GH) therapy have been introduced at age of 3yrs up to 11yrs. Negative molecular testing for PTPN11 and SOS1 genes, normal female karyotype and aCGH analysis were observed. Objective examination: H 138 cm, (<3?); W 33 kg, (<3?), no menarche, hypertelorism, eyelids ptosis with down slanting palpebral fissures, low-set and posteriorly rotated ears, high-arched palate, micrognathia, short and webbed neck, low hairline at the back of the neck, pectus excavatum, prominent scoliosis, joint hyperextensibility, bilateral pes planus and mitral valve prolapse disclosed by US. Phenotype of our patient was suggestive to NS, thus further mutational screening has been requested. Missense mutation in exon 2 of KRAS gene (c.40G>A; p.Val14Ile) has been identified. Even though KRAS mutations are usually associated with NS severe phenotype with cardiac involvement (hypertrophic cardiomyopathy), this finding is not present in our patient.