disease pattern can be recognized

If a disease pattern can be recognized, the next
decision concerns the category of disease. Although
difficult to establish in practice, the disease
category is important for the next steps to
be taken. For this purpose, the McKusick catalog
of human genes and diseases, Mendelian Inheritance
in Man (MIM) and its online version
(OMIM) are indispensable. The possibility of
genetic heterogeneity must be considered at
this stage. The term genetic heterogeneity refers
to a phenotype (disease) that has different
causes. A particular phenotype may be caused
by mutations at different loci (locus heterogeneity)
or by different mutant alleles at the same
locus (allele heterogeneity). All genetic diagnostic
procedures should be preceded by genetic
counseling, which properly includes obtaining
the (informed) consent of the persons involved.