Improved strategy for molecular genetic diagnostics in juvenile nephronophthisis

Juvenile or type 1 nephronophthisis (NPH1), an autosomal recessive cystic k idney disease, represents the most common genetic cause of end-stage renal disease in the first two decades of life. Because the disease is caused by large homozygous deletions of the NPHP1 gene in approximately 66% of patien ts with nephronophthisis, molecular genetic testing offers a method for the definite diagnosis of NPH1 and avoids the invasive procedure of renal biop sy, We recently developed an algorithm for molecular genetic diagnosis of N PH1 that efficiently detects homozygous deletions, However, a major limitat ion remained for the detection of heterozygous deletions that cause NPH1 in combination with point mutations at the other NPHP1 allele, Because a part ial sequence from the NPHP1 region recently became available through the Hu man Genome Projects, we exploited this information to develop novel polymor phic markers from this genetic region for the detection of heterozygous del etions of NPHP1, thus bridging the diagnostic gap, Five novel polymorphic m icrosatellites positioned within the large common NPHP1 deletion were gener ated, Two multiplex polymerase chain reaction sets using two and three poly morphic markers from the NPHP1 deletion region together with one positive c ontrol marker allowed four different diagnostic problems to be solved in on e diagnostic setup: (1) detection of the classic homozygous deletion of NPH 1, (2) detection of a rare smaller homozygous deletion of NPH1, (3) testing for a heterozygous deletion, and (4) potential exclusion of linkage to NPH P1, The newly generated multiplex marker sets will greatly enhance the effi cacy of molecular diagnostics in NPH through improved detection of heterozy gous deletions. (C) 2001 by the National Kidney Foundation, Inc.