MD and CP supported the project. CD and JPH conceived and designed the experiments. CD, LT, and CF performed the experiments. CD and JPH analyzed the data. JL, PB, MLK, JL, ALR, MM, AM, GM, AM, JET, SW, and JY contributed reagents/materials/analysis tools. JPH wrote the paper.
The authors have declared that no competing interests exist.
Kallmann syndrome combines anosmia, related to defective olfactory bulb morphogenesis, and hypogonadism due to gonadotropin-releasing hormone deficiency. Loss-of-function mutations in
Kallmann syndrome is a developmental disease that affects both the hormonal reproductive axis and the sense of smell. In addition, various nonreproductive and nonolfactory anomalies are occasionally observed in a fraction of the patients. There is a developmental link between the reproductive and olfactory disorders: neuroendocrine cells producing the gonadotropin-releasing hormone that is deficient in the patients normally migrate from the nose to the forebrain along olfactory nerve fibers during embryonic life, and they most probably fail to do so in the patients. Affected individuals usually do not undergo spontaneous puberty. Hormone replacement therapy is the treatment to initiate virilization in males or breast development in females, and later, to develop fertility in both sexes. This is a hereditary disease with complex genetic transmission. Mutations in either of two different genes,
Kallmann syndrome (KS) combines hypogonadotropic hypogonadism and anosmia or hyposmia, i.e., a deficiency of the sense of smell [
This is a genetically heterogeneous disease, which affects 1:8000 males and approximately five times less females. Two different genes have so far been identified. Loss-of-function mutations in
Because the common infertility in affected individuals and, most importantly, the incomplete penetrance of the disease impede linkage analysis, the positional cloning strategies that have been taken to find causative genes were based on the analysis of rare KS individuals who carry chromosomal rearrangements detectable by cytogenetics techniques [
We first considered
Filled symbols denote clinically affected individuals with both hypogonadism and anosmia (or hyposmia). Half-filled symbols denote individuals with either anosmia only (right black part) or hypogonadism only (left black part). Genotypes, if available, are indicated below. The symbol + denotes normal allele, and fs stands for frameshift mutation. In several pedigrees the mutation is associated with varying phenotypes. Notably, in family A the disease apparently segregates according to a semi-dominant mode of transmission. The schematic representation of PROKR2 shows the locations of the nine missense mutations found in familial and non-familial KS cases, with respect to the putative N-terminal (N ter), C-terminal (C ter), extracellular loop (e1-e3), intracellular loop (i1-i3), and transmembrane (T1–T7) domains [
Prokineticin-2 (PROK2) [
Considering both the phenotypes of the Prokr2- or Prok2-deficient mice and the likely deleterious effect of the human frameshift mutations on protein synthesis, the various
It is noteworthy that KS patients who carry mutations in
In human monogenic disorders, genuine dominance, where heterozygotes and homozygotes have the same phenotype, is unusual. In particular, most dominant developmental diseases are far more severe in the homozygous state. Therefore, the finding of both heterozygous and homozygous (or compound heterozygous) KS patients for a given mutation in
Written informed consent was obtained from all the individuals who participated in the study. Genomic DNA was obtained from peripheral blood samples or lymphoblastoid cell lines by using a standard phenol chloroform extraction procedure. The genomic DNA from 250 unrelated Caucasian individuals was used as a control (control individuals were not examined to look for Kallmann syndrome features). We used the ENSEMBL (
PROK2_1F: 5′-GGCGGGGCTAGCCTTTAT-3′
PROK2_1R: 5′-CCTCTAGCCTGCCCTTCAG-3′
PROK2_2F: 5′-CCCACTTTCGAAAAATGAGAA-3′
PROK2_2R: 5′-TGTTTGTCGAGCACGTTACC-3′
PROK2_3F: 5′-GGCTTGGCTGTATCTTGCTC-3′
PROK2_3R: 5′-TGGGGCTGAACTGATAGGAC-3′
PROK2_4F: 5′-GGGTAGTTAACGCTCAGTAAACA-3′
PROK2_4R: 5′-GAGCATTTCTTTCTGGCACA-3′
PROKR2_1F: 5′-GGCTCACTGACCCTGAAAGA-3′
PROKR2_1R: 5′-TGTCAGCCTGTCAGAGCCTA-3′
PROKR2_2F: 5′-GGATTCACTGTGCCACTGC-3′
PROKR2_2R: 5′-CCATGCAGCCTATGAACTTG-3′
Normal sequences are shown on the top, mutated sequences at the bottom. Asterisks denote sequences from the non-coding DNA strand. Mutations are indicated by vertical arrows. All the mutations were found in the heterozygous or compound heterozygous state in Kallmann syndrome patients. In addition, two
(2.4 MB TIF)
The missense mutations found in Kallmann syndrome patients are indicated by arrowheads. In the PROK2 sequence, the additional peptide encoded by exon 3 (alternative splicing) is underlined, and the N-terminal AVITGA motif that is critical for the bioactivity of the protein is highlighted in yellow.
(91 KB PDF)
Control electrophoretograms are shown on the top. The mutations in
Alignment of the KAL1 amino acid sequences from man, cow, chicken, zebrafish (kal1.1 and kal1.2),
(943 KB TIF)
We thank all the patients and family members who participated in this study. We are grateful to the Service de Séquençage de l'Institut Cochin for sequencing facilities.
Kallmann syndrome
prokineticin-2
prokineticin receptor-2