A. Sorlin

Molecular diagnosis of PIK3CA -related overgrowth spectrum (PROS) in 162 patients and recommendations for genetic testing

Purpose:Postzygotic activating mutations of PIK3CA cause a wide range of mosaic disorders collectively referred to as PIK3CA-related overgrowth spectrum (PROS). We describe the diagnostic yield and characteristics of PIK3CA sequencing in PROS.Methods:We performed ultradeep next-generation sequencing (NGS) of PIK3CA in various tissues from 162 patients referred to our clinical laboratory and assessed diagnostic yield by phenotype and tissue tested.Results:We identified disease-causing mutations in 66.7% (108/162) of patients, with mutant allele levels as low as 1%. The diagnostic rate was higher (74%) in syndromic than in isolated cases (35.5%; P = 9.03 × 10−5). We identified 40 different mutations and found strong oncogenic mutations more frequently in patients without brain overgrowth (50.6%) than in those with brain overgrowth (15.2%; P = 0.00055). Mutant allele levels were higher in skin and overgrown tissues than in blood and buccal samples (P = 3.9 × 10−25), regardless of the phenotype.Conclusion:Our data demonstrate the value of ultradeep NGS for molecular diagnosis of PROS, highlight its substantial allelic heterogeneity, and confirm that optimal diagnosis requires fresh skin or surgical samples from affected regions. Our findings may be of value in guiding future recommendations for genetic testing in PROS and other mosaic conditions.Genet Med advance online publication 02 February 2017

Vitamin D-dependent rickets type 1B (25-hydroxylase deficiency): a rare condition or a misdiagnosed condition?†

Vitamin D requires a two‐step activation by hydroxylation: The first step is catalyzed by hepatic 25‐hydroxylase (CYP2R1, 11p15.2) and the second one is catalyzed by renal 1α‐hydroxylase (CYP27B1, 12q13.1), which produces the active hormonal form of 1,25‐(OH)2D. Mutations of CYP2R1 have been associated with vitamin D–dependent rickets type 1B (VDDR1B), a very rare condition that has only been reported to affect 4 families to date. We describe 7 patients from 2 unrelated families who presented with homozygous loss‐of‐function mutations of CYP2R1. Heterozygous mutations were present in their normal parents. We identified a new c.124_138delinsCGG (p.Gly42_Leu46delinsArg) variation and the previously published c.296T>C (p.Leu99Pro) mutation. Functional in vitro studies confirmed loss‐of‐function enzymatic activity in both cases. We discuss the difficulties in establishing the correct diagnosis and the specific biochemical pattern, namely, very low 25‐OH‐D suggestive of classical vitamin D deficiency, in the face of normal/high concentrations of 1,25‐(OH)2D. Siblings exhibited the three stages of rickets based on biochemical and radiographic findings. Interestingly, adult patients were able to maintain normal mineral metabolism without vitamin D supplementation. One index case presented with a partial improvement with 1alfa‐hydroxyvitamin D3 or alfacalcidol (1α‐OH‐D3) treatment, and we observed a dramatic increase in the 1,25‐(OH)2D serum concentration, which indicated the role of accessory 25‐hydroxylase enzymes. Lastly, in patients who received calcifediol (25‐OH‐D3), we documented normal 24‐hydroxylase activity (CYP24A1). For the first time, and according to the concept of personalized medicine, we demonstrate dramatic improvements in patients who were given 25‐OH‐D therapy (clinical symptoms, biochemical data, and bone densitometry). In conclusion, the current study further expands the CYP2R1 mutation spectrum. We note that VDDR1B could be easily mistaken for classical vitamin D deficiency.

Performance of Semiconductor sequencing platform for non‐invasive prenatal genetic screening for fetal aneuploidies: results from a multicenter prospective cohort study in a clinical setting

To validate and evaluate the performance metrics of the high‐throughput semiconductor sequencing platform, Ion Proton®, in non‐invasive prenatal genetic screening (NIPS) for common fetal aneuploidies in a clinical setting.

McCune–Albright syndrome, natural history and multidisciplinary management in a series of 14 pediatric cases

BACKGROUND McCune-Albright syndrome is a rare disorder characterized by endocrine disorders, café-au-lait spots and fibrous dysplasia of bone that occurs early in life. METHODS A series of 14 pediatric cases were followed between 1994 and 2013 by the competence center for rare endocrine diseases and constitutional bone diseases at CHU de Nancy (France). The diagnosis is based on the presence of at least two symptoms. RESULTS The mean follow-up was 6 years (1-17 years). The sex ratio was six girls per boy. The incidence was 0.28 cases/million population/year. Mean age at diagnosis was 6 years. A mutation in the GNAS gene was found in 33% of patients tested. Gonadal involvement (13/14 cases), including early peripheral puberty and ovarian cysts in girls (82%) occurred on average at 4 years of age. Bone involvement (10/14 cases) appeared on average at 5 years of age and was most often multiple (80%) with fracture risk, and the skull, with a neurosensory risk. CONCLUSION Clinical definition and methods of screening and monitoring can be improved to allow for an earlier intervention. It must be multidisciplinary and take into account the disability and quality of life of the patient.