Discussion
Phenotypically Noonan syndrome especially in female share similar
features with Turner syndrome such as short stature, webbed neck, wide
space nipple, mental retardation, urogenital and cardiac abnormalities,
and craniofacial dysmorphism. Karyotyping is the only investigation on
the basis of which we can differentiate between these two conditions.
[5] Noonan syndrome is a genetic condition and the common mutations
involve are PTPN11, SOS1, RAF1, KRAS, NRAS, and BRAF genes. Among these
mutations, PTPN11 gene mutations account for about 50%, SOS1 gene
mutation for 10%–15%, and RAF1 gene mutation for 5%–10% of Noonan
syndrome. KRAS, NRAS, and BRAF genes account for a relatively small
percentage of Noonan syndrome. [6, 7] Diagnosis of Noonan syndrome
can be made either by genetic testing or clinical diagnostic criteria.
Both are equally specific because 25 percent of the genetic testing for
Noonan syndrome is nonconclusive. The scoring system for the diagnosis
of Noonan syndrome was developed by Van der Burgt et al in 1997 which
are made of 6 major features and 6 minor features. According to this
criteria, Noonan syndrome can be diagnosed with typical facial features
plus 1 major or 2 minor characteristics or suggestive facial features
plus 2 major or 3 minor signs. [8] Our patient had typical facial
features with 1 major criterion i.e. short stature (below 3rd
percentile). The following shows table shows the scoring system for
Noonan syndrome (Table.2)
Differential diagnoses of Noonan syndrome include Turner syndrome (45,
XO), Cardio-Facio-Cutaneous (CFC) syndrome, Costello syndrome,
Neurofibromatosis type 1 (NF1), and LEOPARD syndrome. Syndromes that are
characterized by facial dysmorphology, short stature, and cardiac
defects may sometimes be difficult to differentiate from NS, notably
Williams syndrome and Aarskog syndrome. As the syndrome has a wide
spectrum of disorders, patients with Noonan syndrome have to undergo
hematological investigations, karyotyping and mutation analysis cardiac
investigations, and Assessment of development (IQ, Identifying any
delays, mental retardation). [9,10]
Previously a study has shown the association between hypothyroidism and
Noonan’s syndrome although few studies report autoimmune thyroiditis the
cause is unknown, but factors that may predispose to the condition
include genetics, high iodine consumption, and age. Vesterhus P et al in
a study showed thyroid antibodies were found to be more common in Noonan
syndrome, but hypothyroidism is not more common in Noonan syndrome
compared to the general population. [11,12] There is no single
treatment available for Noonan syndrome, a multidisciplinary approach is
needed to address the patient’s concerns and to treat the complications
or associated conditions.