Stephanie M. Karle

Patients with Mutations in NPHS2 (Podocin) Do Not Respond to Standard Steroid Treatment of Nephrotic Syndrome

Nephrotic syndrome (NS) represents the association of proteinuria, hypoalbuminemia, edema, and hyperlipidemia. Steroid-resistant NS (SRNS) is defined by primary resistance to standard steroid therapy. It remains one of the most intractable causes of ESRD in the first two decades of life. Mutations in the NPHS2 gene represent a frequent cause of SRNS, occurring in approximately 20 to 30% of sporadic cases of SRNS. On the basis of a very small number of patients, it was suspected that children with homozygous or compound heterozygous mutations in NPHS2 might exhibit primary steroid resistance and a decreased risk of FSGS recurrence after kidney transplantation. To test this hypothesis, NPHS2 mutational analysis was performed with direct sequencing for 190 patients with SRNS from 165 different families and, as a control sample, 124 patients with steroid-sensitive NS from 120 families. Homozygous or compound heterozygous mutations in NPHS2 were detected for 43 of 165 SRNS families (26%). Conversely, no homozygous or compound heterozygous mutations in NPHS2 were observed for the 120 steroid-sensitive NS families. Recurrence of FSGS in a renal transplant was noted for seven of 20 patients with SRNS (35%) without NPHS2 mutations, whereas it occurred for only two of 24 patients with SRNS (8%) with homozygous or compound heterozygous mutations in NPHS2. None of 29 patients with homozygous or compound heterozygous mutations in NPHS2 who were treated with cyclosporine A or cyclophosphamide demonstrated complete remission of NS. It was concluded that patients with SRNS with homozygous or compound heterozygous mutations in NPHS2 do not respond to standard steroid treatment and have a reduced risk for recurrence of FSGS in a renal transplant. Because these findings might affect the treatment plan for childhood SRNS, it might be advisable to perform mutational analysis of NPHS2, if the patient consents, in parallel with the start of the first course of standard steroid therapy.

Bladder exstrophy and Epstein type congenital macrothrombocytopenia: evidence for a common cause?

Boris Utsch,* Analisa DiFeo, Annegret Kujat, Stephanie Karle, Volker Schuster, Harald Lenk, Ulla Jacobs, Martin Müller, Jörg Dötsch, Wolfgang Rascher, Heiko Reutter, John A. Martignetti, Michael Ludwig, and Ralf-Bodo Tröbs Department of Pediatrics, University of Erlangen-Nuremberg, Erlangen, Germany Department of Human Genetics, Mount Sinai School of Medicine, New York, NY Department of Human Genetics, University of Leipzig, Leipzig, Germany Department of Pediatrics, University of Leipzig, Leipzig, Germany Department of Human Genetics, University of Bonn, Bonn, Germany Department of Clinical Biochemistry, University of Bonn, Bonn, Germany Department of Pediatric Surgery, University of Leipzig, Leipzig, Germany

Infantile hypophosphatasia due to a new compound heterozygous TNSALP mutation - functional evidence for a hydrophobic side-chain?

BACKGROUND Infantile hypophosphatasia (IH) is an inherited disorder characterized by defective bone mineralization and a deficiency of alkaline phosphatase activity. OBJECTIVE/DESIGN The aim of the study was to evaluate a new compound heterozygous TNSALP mutation for its residual enzyme activity and localization of the comprised amino acid residues in a 3D-modeling. PATIENT We report on a 4-week old girl with craniotabes, severe defects of ossification, and failure to thrive. Typical clinical features as low serum alkaline phosphatase, high serum calcium concentration, increased urinary calcium excretion, and nephrocalcinosis were observed. Vitamin D was withdrawn and the patient was started on calcitonin and hydrochlorothiazide. Nonetheless, the girl died at the age of 5 months from respiratory failure. RESULTS Sequence analysis of the patients TNSALP gene revealed two heterozygous mutations [c.653T>C (I201T), c.1171C>T (R374C)]. Transfection studies of the unique I201T variant in COS-7 cells yielded a mutant TNSALP protein with only a residual enzyme activity (3.7%) compared with wild-type, whereas the R374C variant was previously shown to reduce normal activity to 10.3%. 3D-modeling of the mutated enzyme showed that I201T resides in a region that does not belong to any known functional site. CONCLUSION We note that I201, which has been conserved during evolution, is buried in a hydrophobic pocket and, therefore, the I>T-change should affect its functional properties. Residue R374C is located in the interface between monomers and it has been previously suggested that this mutation affects dimerization. These findings explain the patients clinical picture and severe course.