The MENDEL-study will investigate whether the use of gene panel or whole genome sequencing (WGS) will:

1. improve the rate of diagnosis and through this compare the performance of the two diagnostic approaches (gene panel vs. WGS),
2. investigate whether use of said sequencing approaches early in the diagnostic process results in reduced health care spending, and
3. result in an improved quality of life for the patients and their parents.

Patients will be recruited from in- and outpatient clinics at the Otto Heubner Center, the Berlin Center for Rare Diseases, and the Institute for Medical Genetics and Human Genetics at Charité-Universitätsmedizin Berlin, Germany. Following informed consent, 5 ml EDTA blood will be obtained from the index case and 10 ml blood from each parent. Disease related phenotype information and the outcome of previous diagnostic tests and procedures will be recorded as part of Study visit #1.

[1] Study visit #1

1. A medical genetics physical will be performed. Detailed clinical symptoms (phenotype) will be recorded using Human Phenotype Ontology (HPO) terminology.
2. A detailed pedigree will be drawn.
3. Age of disease onset will be determined.
4. Results from previous diagnostic tests and procedures, as well as hospital stays, will be recorded.
5. The parents will be asked to complete a validated, standardized quality of life questionnaire adapted for for rare disease. The questionnaire is available online or in paper form.

[2] Study visit #2a (optional)

This study visit will only take place in the event that gene panel sequencing identifies a variant of uncertain significance, where additional information would be needed in order to determine its pathogenicity (e.g. confirmational biochemical testing, collection of additional information). Relevant research findings will be discussed and the nature and necessity of the additional testing will be explained.

[3] Study visit #2b (optional)

This study visit will only take place in the event that WGS identifies a variant of uncertain significance where additional information is needed in order to determine its pathogenicity > see Study visit #2a.

[4] Study visit #3 (results session)

Results will be returned in the context of a genetic counseling session.

[5] Study visit #4 (6 months after Study visit #3)

The parents will be asked to complete the validated, standardized quality of life questionnaire adapted for rare disease again.

Inclusion Criteria:

1. Diagnosis: Suspicion of genetic disease. (Only one of the following criteria is required.) [1.1] Family member(s) with similar phenotype OR [1.2] At least two affected organ systems OR [1.3] One affected organ system that is known to be associated with multiple disease causing genes (e.g. long QT syndrome) OR [1.4] Multiple birth defects
2. Both parents must be available for blood draw in order to confirm phase (segregation analysis) or in order to perform WGS of the trio at a later time point.
3. Age: from birth up until age 18 years
4. Gender: Both sexes will be included

Exclusion Criteria:

1. Suspicion that the phenotype is due to an acquired disease
2. Missing informed consent from both parents or from all legal guardians for genetic testing in the setting of a clinical trial.
3. Clinical diagnosis of a disease with a known monogenic cause, e.g. Phenylketonuria or Cystic fibrosis.

Index patients: Children (age newborn to 18 years) who present with a suspected genetic disorder

Parents: biological mother and father of each index case.