Acute intermittent porphyria: novel missense mutations in the human hydroxymethylbilane synthase gene

PURPOSE

To identify mutations in families with acute intermittent porphyria, an autosomal dominant inborn error of metabolism that results from the half-normal activity of the third enzyme in the heme biosynthetic pathway, hydroxymethylbilane synthase.

METHODS

Mutations were identified by direct solid phase sequencing.

RESULTS

Two novel missense mutations E80G and T78P and three previously reported mutations, R173W, G111R, and the splice site lesion, IVS1+1, were detected, each in an unrelated proband. The causality of the novel missense mutations was demonstrated by expression studies.

CONCLUSION

These findings provide for the precise diagnosis of carriers in these families and further expand the molecular heterogeneity of AIP.

The role of EC 3.4.24.15 in the post-secretory regulation of peptide signals

In the present studies, we characterized the degradation of gonadotropin-releasing hormone (GnRH) by tissues of the ovine hypothalamo-pituitary axis. Membrane and soluble fractions of the medial basal hypothalamus, the pre-optic area, the median eminence and the anterior pituitary demonstrated greater GnRH-degrading activity than either hypophysial-portal or jugular plasma. The primary stable product of the membrane fractions was GnRH1-3, while the major product of the soluble fractions was GnRH1-5, both fragments were generated by plasma. Of all tissue fractions, the highest specific activity was observed in the soluble median eminence. Partial purification and characterization of soluble hypothalamic peptidase activity suggested that GnRH degradation by this tissue occurs via a two-step mechanism involving both post-proline cleaving enzyme and the metalloendopeptidase 3.4.24.15.