Turner syndrome is found only in females. It is differentiated from Noonan syndrome by demonstration of a sex chromosome abnormality on cytogenetic (chromosome) studies. In Turner syndrome, kidney problems are more common, developmental delay is much less frequently found, and left-sided heart defects occur more often.
Watson syndrome is characterized by short stature, pulmonary valve stenosis, variable intellectual development, and café au lait spots. Watson syndrome also overlaps with neurofibromatosis type 1 .
Cardiofaciocutaneous (CFC) syndrome and Noonan syndrome have the greatest overlap in features. CFC syndrome has similar cardiac and lymphatic findings. In CFC syndrome, intellectual disability is usually more severe, gastrointestinal problems are more severe, and bleeding problems are rare. Four genes are known to cause CFC syndrome including BRAF (~75%), MAP2K1 and MAP2K2 (~25%), and KRAS (<2%-3%).
Costello syndrome shares features with both Noonan syndrome and Cardiofaciocutaneous (CFC) syndrome. Many individuals with Costello syndrome have had genetic testing and no changes in PTPN11 have been found. Genetic changes in HRAS have been shown to cause Costello syndrome.
Noonan syndrome-like disorder with or without JMML is caused by variants in CBL. This condition is characterized by neurologic features, predisposition to juvenile myelomonocytic leukemia, low risk of cardiac defects, reduced growth, and cryptorchidism (undescended testes).
Neurofibromatosis type 1 (NF1) shares some features with Noonan syndrome, including short stature, learning difficulties, and café au lait spots.
Speak to a genetic counselor or a medical geneticist to learn more about these conditions.
