Diagnostic approaches to apparent homozygosity

Area of Science:

• Genetics
• Molecular Biology
• Diagnostic Medicine

Background:

• Sanger sequencing is a standard method for gene mutation identification in molecular diagnostics.
• Autosomal recessive disorders can present challenges, with heterozygous mutations sometimes appearing homozygous due to amplification failures.

Purpose of the Study:

• To determine the frequency of apparently homozygous mutations in autosomal recessive disorders being caused by other molecular etiologies.
• To investigate the reliability of Sanger sequencing in identifying homozygous mutations for genetic testing.

Main Methods:

• Reviewed 12,406 cases across 40 genetic tests analyzed by Sanger sequencing.
• Investigated the molecular status of 291 apparently homozygous cases through parental testing and other molecular methods.

Main Results:

• Identified 291 cases of apparent homozygosity, with frequencies varying by gene.
• Parental carrier status was confirmed in 88% of investigated cases.
• Identified deletions, allele dropout, and uniparental isodisomy as causes for apparent homozygosity in remaining cases.

Conclusions:

• Parental testing is essential to confirm diagnoses in individuals with apparent homozygous mutations for autosomal recessive disorders.
• Confirmatory testing can differentiate true homozygosity from other molecular events like allele dropout, copy number variations, and uniparental isodisomy.