Diagnostic yield of various genetic approaches in patients with unexplained developmental delay or mental retardation.
The underlying cause of mental retardation remains unknown in up to 80% of patients. As chromosomal aberrations are the most common known cause of mental retardation, several new methods based on FISH, PCR, and array techniques have been developed over recent years to increase detection rate of subtle aneusomies initially of the gene rich subtelomeric regions, but nowadays also genome wide. As the reported detection rates vary widely between different reports and in order to compare the diagnostic yield of various investigations, we analyzed the diagnostic yield of conventional karyotyping, subtelomeric screening, molecular karyotyping, X-inactivation studies, and dysmorphological evaluation with targeted laboratory testing in unselected patients referred for developmental delay or mental retardation to our cytogenetic laboratory (n = 600) and to our genetic clinic (n = 570). In the cytogenetic group, 15% of patients showed a disease-related aberration, while various targeted analyses after dysmorphological investigation led to a diagnosis in about 20% in the genetic clinic group. When adding the patients with a cytogenetic aberration to the patient group seen in genetic clinic, an etiological diagnosis was established in about 40% of the combined study group. A conventional cytogenetic diagnosis was present in 16% of combined patients and a microdeletion syndrome was diagnosed in 5.3%, while subtelomeric screening revealed only 1.3% of causes. Molecular karyotyping with a 10 K SNP array in addition revealed 5% of underlying causes, but 29% of all diagnoses would have been detectable by molecular karyotyping. In those patients without a clear diagnosis, 5.6% of mothers of affected boys showed significant (>95%) skewing of X-inactivation suggesting X-linked mental retardation. The most common diagnoses with a frequency of more than 0.5% were Down syndrome (9.2%), common microdeletion 22q11.2 (2.4%), Williams-Beuren syndrome (1.3%), Fragile-X syndrome (1.2%), Cohen syndrome (0.7%), and monosomy 1p36.3 (0.6%). From our data, we suggest the following diagnostic procedure in patients with unexplained developmental delay or mental retardation: (1) Clinical/dysmorphological investigation with respective targeted analyses; (2) In the remaining patients without an etiological diagnosis, we suggest conventional karyotyping, X-inactivation screening in mothers of boys, and molecular karyotyping, if available. If molecular karyotyping is not available, subtelomeric screening should be performed.
Rauch
Anita
A
Institute of Human Genetics, Friedrich-Alexander University Erlangen-Nuremberg, Erlangen, Germany. arauch@humgenet.uni-erlangen.de
Hoyer
Juliane
J
Guth
Sabine
S
Zweier
Christiane
C
Kraus
Cornelia
C
Becker
Christian
C
Zenker
Martin
M
Hüffmeier
Ulrike
U
Thiel
Christian
C
Rüschendorf
Franz
F
Nürnberg
Peter
P
Reis
André
A
Trautmann
Udo
U
D002675:Child, Preschool; D002869:Chromosome Aberrations; D003582:Cytogenetics; D002658:Developmental Disabilities / Q000235:genetics*; D005260:Female; D030342:Genetic Diseases, Inborn / Q000175:diagnosis / Q000235:genetics; D005820:Genetic Testing; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008607:Intellectual Disability / Q000235:genetics*; D008297:Male; D038901:X-Linked Intellectual Disability / Q000175:diagnosis / Q000235:genetics; D010641:Phenotype; D013577:Syndrome; D049951:X Chromosome Inactivation