Scientific Basis for a Newborn Screening for Cystinosis and Primary Hyperoxaluria

Background and aims. Population-based newborn screening (NBS) is an important public health program that has vastly improved the course of several diseases through early detection. The selection of screened disorders generally follows the 10 principles outlined by Wilson and Jungner. In Germany, NBS has been a voluntary National Health Service program since 1969 which currently covers 17 disorders. Current NBS methods, which employ tandem mass-spectrometric analysis of newborn dried blood spots, cannot detect many potentially treatable genetic conditions. At the same time, molecular-based NBS is increasingly feasible because DNA can be extracted from a dried blood spot, next generation sequencing has become economical, and molecular diagnostics have greater reliability and increased validity as genetic databases become more refined and comprehensive. Nephropathic cystinosis and hyperoxaluria (PH) are eligible for molecular-based NBS because effective therapies are available.

In a first pilot project, the scientific basis for NBS for cystinosis could already be established. The aim of this study is to demonstrate the transferability of genetic NBS for Cystinosis to other laboratories and to lay the scientific basis for screening for PH.

Specifically, the study will investigate whether the inclusion of these diseases into general NBS should be recommended. By observing the identified infants in comparison to patients symptomatically diagnosed outside of the pilot project, it will be determined whether and to what extent early diagnosis and therapy lead to a more favorable prognosis.

Cystinosis Nephropathic cystinosis, due to impaired transport of cystine out of lysosomes, occurs with an incidence of 1 in 100-200,000 live births. It is characterized by renal Fanconi syndrome in the first year of life and glomerular dysfunction progression to end-stage kidney disease by approximately 10 years of age. Treatment with oral cysteamine therapy helps preserve glomerular function, but affected individuals eventually require kidney replacement therapy Cysteamine treatment generally begins at the time of diagnosis in the second year of life, but some glomerular and tubular damage has already occurred by then. This situation could be ameliorated by diagnosing patients shortly after birth, employing molecular genetics-based newborn screening. Standard mass spectrometry-based methods for newborn screening cannot detect the increased cystine content of cystinosis leukocytes.

For cystinosis screening, the first tier involved multiplex PCR to detect two of the three most common CTNS mutations in Germany. Heterozygous samples will be submitted to amplicon-based next-generation sequencing for 175 pathogenic CTNS mutations (Labor Limbach, Mainz). A detection rate of 96.5% is predicted using this approach.