Hardelin et al. (1993) reported results of a mutation search of the KAL1 gene in 21 unrelated males with familial Kallmann syndrome. In 2 families, large deletions that included the entire KAL gene were detected by Southern blot analysis. By sequencing each of the 14 coding exons and splice site junctions in the other 19 patients, they found 9 point mutations at separate locations in 4 exons and 1 splice site. They emphasized the high frequency of unilateral renal aplasia in X-linked Kallmann syndrome patients; 6 of 11 males with identified alterations of the KAL gene showed this feature.
As a mitochondrial P450 system, P450c11 is dependent on two electron transfer proteins, adrenodoxin reductase and adrenodoxin that transfer 2 electrons from NADPH to the P450 for each monooxygenase reaction catalyzed by the enzyme. In most respects this process of electron transfer appears similar to that of P450scc system that catalyzes cholesterol side chain cleavage.  Similar to P450scc the process of electrons transfer is leaky leading to superoxide production. The rate of electron leakage during metabolism depends on the functional groups of the steroid substrate. 
Hermanussen and Sippell (1985) reported a presumably X-linked recessive kindred. All carrier females had normal sexual and olfactory function. Hipkin et al. (1990) described male twins who were identical by DNA fingerprinting; one had full-blown manifestations of Kallmann syndrome, whereas the other showed normal sexual development and only hyposmia. In a second family, Hermanussen and Sippell (1985) observed 16-year-old twin sisters of whom one had retarded pubertal development and total anosmia, and the other, proven to be monozygotic by blood grouping and HLA typing, had undergone a normal menarche but showed total anosmia. The authors pointed out that sporadic cases of Kallmann syndrome have appeared only in families in which isolated anosmia (see 301700 , 107200 ) is present. They suggested that there is an acquired hypothalamic GnRH deficiency on the basis of preexisting anosmia.