Compound heterozygote

Compound Heterozygote

A compound heterozygoterefers to an individual who has two different mutant alleles at a particular gene locus, one on each chromosome of a pair. This genetic condition can lead to a recessive genetic disorder if both alleles result in a loss of function of the gene product. Compound heterozygosity is a common occurrence in many genetic diseases, where the presence of two different mutations can result in a similar phenotype to that seen in individuals who are homozygous for a single mutation.

Genetic Basis

In humans, most genes are present in two copies, one inherited from each parent. A compound heterozygote has two different mutations at a specific locus, each inherited from one parent. This is in contrast to a homozygote, who has two identical alleles at a locus, and a heterozygote, who has one normal and one mutant allele.

Compound heterozygosity can occur in autosomal recessive disorders, where two defective alleles are necessary to express the disease phenotype. Each parent of a compound heterozygote typically carries one mutant allele, making them carriers of the disorder.

Examples of Disorders

Several genetic disorders can result from compound heterozygosity, including:

• Cystic Fibrosis: This condition is often caused by compound heterozygosity for different mutations in the CFTR gene. Different combinations of mutations can lead to varying severities of the disease.

• Phenylketonuria (PKU)]]: Individuals with PKU may be compound heterozygotes for different mutations in the PAH gene, which encodes the enzyme phenylalanine hydroxylase.

• Tay-Sachs Disease: This neurodegenerative disorder can also result from compound heterozygosity in the HEXA gene.

Diagnosis

The diagnosis of compound heterozygosity typically involves genetic testing, such as sequencing of the gene of interest to identify the specific mutations present. Genetic counseling is often recommended for families with a history of genetic disorders to understand the risks and implications of compound heterozygosity.

Clinical Implications

The clinical presentation of a compound heterozygote can vary depending on the specific mutations involved. Some mutations may result in a complete loss of function, while others may retain partial activity. The combination of these mutations can influence the severity and progression of the disease.

Also see

• Homozygote
• Heterozygote
• Autosomal recessive inheritance
• Genetic counseling