Genetically determined low C4: a predisposing factor to autoimmune chronic active hepatitis

Area of Science:

• Immunology
• Genetics
• Hepatology

Background:

• Autoimmune chronic active hepatitis (CAH) is an inflammatory liver disease.
• Complement system deficiencies, particularly C4, are implicated in autoimmune disorders.

Purpose of the Study:

• To investigate the prevalence and potential genetic basis of low C4 serum levels in children with autoimmune CAH.

Main Methods:

• Serum C3 and C4 levels were measured in patients and their families.
• Transferrin, albumin, C3d, and C4d levels were assessed to rule out other causes of low C4.
• C4 phenotyping was performed on patients and parents to identify null allotypes.

Main Results:

• 18 of 26 (69%) pediatric CAH patients had low C4 levels; 5 (19%) had low C3.
• Family studies revealed a higher incidence of low C4 in parents and siblings of affected probands.
• C4 phenotyping showed a significantly higher prevalence of null allotypes in CAH patients (90%) and parents (81%) compared to controls (59%).

Conclusions:

• Low C4 levels in autoimmune CAH are likely genetically determined.
• Defective expression of C4 structural genes may contribute to C4 deficiency and susceptibility to CAH.