Kees Noordam

Genotypic and phenotypic characterization of Noonan syndrome : New data and review of the literature

Noonan syndrome (NS) is an autosomal dominant disorder, characterized by short stature, minor facial anomalies, and congenital heart defects. In approximately 50% of cases the condition is caused by missense mutations in the PTPN11 gene on chromosome 12, resulting in a gain of function of the protein SHP‐2. In this study, PTPN11 mutation analysis was performed in 170 NS patients. In 76 (45%) of them a mutation was identified. We report on the distribution of these mutations, as well as on genotype–phenotype relationships. The benefit of the NS scoring system developed by van der Burgt et al. [( 1994 ); Am J Med Genet 53:187–191] is shown, among physicians who consequently based their diagnosis on the NS scoring system the percentage mutation positive subjects was 54%, whereas this percentage was only 39% among physicians who made less use of the scoring system. In two patients with some uncommon manifestations mutations were found in the C‐SH2 domain, a region in which defects are not often identified in NS. A trend was observed in patients carrying the 922A → G change (Asn308Asp) receiving normal education. In one patient with NS and mild juvenile myelomonocytic leukemia (JMML) the mutation 218C → T (Thr73Ile) was found. This confirms previous findings indicating that individuals with NS with specific mutations in PTPN11 are at risk of developing JMML.

Cancer risk in patients with Noonan syndrome carrying a PTPN11 mutation

Noonan syndrome (NS) is characterized by short stature, facial dysmorphisms and congenital heart defects. PTPN11 mutations are the most common cause of NS. Patients with NS have a predisposition for leukemia and certain solid tumors. Data on the incidence of malignancies in NS are lacking. Our objective was to estimate the cancer risk and spectrum in patients with NS carrying a PTPN11 mutation. In addition, we have investigated whether specific PTPN11 mutations result in an increased malignancy risk. We have performed a cohort study among 297 Dutch NS patients with a PTPN11 mutation (mean age 18 years). The cancer histories were collected from the referral forms for DNA diagnostics, and by consulting the Dutch national registry of pathology and the Netherlands Cancer Registry. The reported frequencies of cancer among NS patients were compared with the expected frequencies using population-based incidence rates. In total, 12 patients with NS developed a malignancy, providing a cumulative risk for developing cancer of 23% (95% confidence interval (CI), 8–38%) up to age 55 years, which represents a 3.5-fold (95% CI, 2.0–5.9) increased risk compared with that in the general population. Hematological malignancies occurred most frequently. Two malignancies, not previously observed in NS, were found: a malignant mastocytosis and malignant epithelioid angiosarcoma. No correlation was found between specific PTPN11 mutations and cancer occurrence. In conclusion, this study provides first evidence of an increased risk of cancer in patients with NS and a PTPN11 mutation, compared with that in the general population. Our data do not warrant specific cancer surveillance.

Genetics and variation in phenotype in Noonan syndrome.

Noonan syndrome is a well-known clinical entity comprising multiple congenital anomalies characterized by typical facial features, short stature and congenital heart defect. Approximately 50% of cases are sporadic. Familial cases are generally autosomal dominant. In 2001 a gene responsible for Noonan syndrome, PTPN11, encoding for the non-receptor protein tyrosine phosphatase SHP-2, was identified. Mutation analysis of the PTPN11 gene was carried out in Nijmegen in 150 patients with Noonan syndrome. Mutations were found in 68 patients (45%), the most common being A922G in exon 8. In exon 4 a mutation was found that encoded the C-SH2 domain of the PTPN11 gene in two unique patients who shared some uncommon features. A 218C→T mutation was found in exon 3 in one patient with Noonan syndrome and mild juvenile myelomonocytic leukaemia.

Denys–Drash syndrome and congenital diaphragmatic hernia: Another case with the 1097G > A(Arg366His) mutation†

Congenital diaphragmatic hernia (CDH) is a disorder of the development of the lung and diaphragm and is associated with pulmonary hypoplasia and pulmonary hypertension. Denys–Drash syndrome (DDS) is a well‐known syndrome caused by several different germline mutations in the WT1‐gene. CDH in DDS is rare. We present the third case of CDH with clinical features of DDS and the same, rare Arg366His mutation in the WT1‐gene, as reported in the other two known cases. This report provides additional evidence that WT1 mutations can result in diaphragmatic hernia.

Expanding the genetic spectrum of Noonan syndrome

Background: The autosomal-dominant Noonan syndrome (MIM 163950) is characterized by short stature, typical facial dysmorphology and heart defects. Noonan syndrome is genetically heterogeneous. Over the last few years, germline mutations in four genes have been found in people with clinical signs of Noonan syndrome, accounting for approximately 65% of cases. All four genes encode proteins involved in the Ras–mitogen-activated protein kinase pathway and result in upregulation of this pathway. Recently, more data on final height after long-term growth hormone (GH) therapy has become available that shows its effectiveness in increasing final height for individuals with Noonan syndrome. Conclusions: The genetics underlying Noonan syndrome has been partially clarified over the last 5 years and further findings will undoubtedly be reported in the next few years. GH therapy has been used to treat patients with Noonan syndrome for approximately 15 years and is effective in improving adult height in affected children.

Spinal stenosis with paraparesis in albright hereditary osteodystrophy. Case report and review of the literature.

We describe thoracic spinal stenosis with progressive myelopathy in association with Albright hereditary osteodystrophy (AHO) in a 12-year-old child with delayed diagnosis and review the relevant literature in order to identify the pathophysiological mechanism. The child was successfully treated by decompressive upper thoracic laminoplasty with full neurological recovery. The pathological changes of the skin also dissolved. Ten more cases of myelopathy and paraparesis in association with AHO, of whom two were children, could be found in the literature. Basically, two different causes for the spinal canal stenosis could be identified: abnormal ossifications of ligaments and congenital narrow spinal canal due to short vertebral pedicles. Awareness of structural spinal column changes in AHO is essential in order to appreciate the neurological symptoms of a beginning myelopathy before irreversible damage to the myelum occurs.

Benign course after acute high dose levothyroxine intoxication in a 3-year-old boy

Abstract. Acute ingestion of thyroid hormone preparations is a common intoxication, with 181 cases in children <12 yr in 2009 in the Netherlands, but generally has a mild course. However, some reports show that even low dosages may cause serious events such as seizures, thyroid storm and coma. We report a 3 yr old boy case with an acute intoxication with high dose levothyroxine (0.5 mg/kg). We describe the proper management of levothyroxine intoxication in children. A 3-year-old boy with no notable medical history ingested sixty tablets of levothyroxine 150 µg. His vital-signs were normal and the only symptom during admission was a tachycardia the following day. Laboratory data showed elevated T3, fT3 and fT4 levels; and decrease TSH levels. He was treated prophylactically and therapeutically with activated charcoal and propranolol. Despite very high levels, his clinical symptoms were relatively mild. After clinical follow-up for 3 d he was discharged. We propose that children with thyroid hormone intoxication with either a levothyroxine dose >0.1 g/kg, a short interval since ingestion, symptomatic presentation, and/or a fT4 >100 pmol/l should be monitored in the hospital during at least 48–72 h post-ingestion and on an outpatient basis for 14 d.