Multiple identification of a particular type of hereditary C1q deficiency in the Turkish population: Review of the cases and additional genetic and functional analysis

Complete selective deficiencies of the complement component C1q are rare genetic disorders that are associated with recurrent infections and a high prevalence of lupus erythematosus-like symptoms. All C1q deficiencies studied at the genetic level revealed single-base mutations leading to termination codons, frameshifts or amino acid exchanges and these were thought to be responsible for the defects as no other aberrations were found. One particular mutation, leading to a stop codon in the C1qA gene, was first identified in members of a Gypsy family from the Slovak Republic. The same mutation has been found in all cases of C1q deficiency from Turkey that have been investigated. Here we present the results of genetic analysis of the C1q genes from three families and give information on further C1q-deficient members of two families that have not been reported elsewhere. Reviewing all cases of C1q deficiency from Turkey prompted us to hypothesize that one particular defective allele is present in the population of southeast Europe and Turkey. With a novel polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis and allele-specific PCR we are able to detect even asymptomatic, heterozygous carriers of the mutation, which will enable genetic counseling of the affected individuals.