Kallmann syndrome associated with complex chromosome rearrangement

Hypergonadotropic hypogonadism and chromosomal aberrations: clinical heterogeneity and implications on the health of elderly men, case series

BACKGROUND

Hypogonadism in older men is often considered as late onset hypogonadism. However, this clinical condition results from primary testicular failure which could be of genetic origin with Klinefelter syndrome being the most common chromosomal abnormality associated with it.

CASE PRESENTATION

We report a heterogeneous group of cases who were diagnosed with hypergonadotropic hypogonadism in their adulthood and were found to have rare chromosomal aberrations. All were elderly men (in their 70 s and 80 s) for whom the diagnosis was made during the evaluation of incidental symptoms suggestive of endocrinopathy. The first had hyponatremia; the other two had gynaecomastia and features of hypogonadism noted during admission for various acute medical problems. With respect to their genetic results; the first had a male karyotype with balanced reciprocal translocation between the long arm of chromosome 4 and the short arm of chromosome 7. The second case had a male karotype with one normal X chromosome and an isochrome for the short arm of the Y chromosome. The third case was an XX male with unbalanced translocation between the X & Y chromosomes with retention of the SRY locus.

CONCLUSION

Hypergonadotrophic hypogonadism in the elderly, may be due to chromosomal aberrations, resulting in heterogeneous and diverse clinical phenotypes. Vigilance must be exercised when seeing cases with subtle clinical findings. This report suggests that in selected cases of adult hypergonadotropic hypogonadism, chromosomal analysis may be indicated.

Clinical manifestations of impaired GnRH neuron development and function

Gonadotropin-releasing hormone (GnRH) and olfactory neurons migrate together in embryologic development, and disruption of this process causes idiopathic hypogonadotropic hypogonadism (IHH) with anosmia (Kallmann syndrome (KS)). Patients with IHH/KS generally manifest irreversible pubertal delay and subsequent infertility due to deficient pituitary gonadotropins or GnRH. The molecular basis of IHH/KS includes genes that: (1) regulate GnRH and olfactory neuron migration; (2) control the synthesis or secretion of GnRH; (3) disrupt GnRH action upon pituitary gonadotropes, or (4) interfere with pituitary gonadotropin synthesis or secretion. KS patients may also have midline facial defects indicating the diverse developmental functions of genes involved. Most causative genes cause either normosmic IHH or KS except FGFR1, which may cause either phenotype. Recently, several balanced chromosomal translocations have been identified in IHH/KS patients, which could lead to the identification of new disease-producing genes. Although there are two cases reported who have digenic disease, this awaits confirmation in future larger studies. The challenge will be to determine the importance of these genes in the 10-15% of couples with normal puberty who have infertility.

Renal dysgenesis and KAL1 gene defects in patients with sporadic Kallmann syndrome

OBJECTIVE

To correlate the presence of renal agenesis/dysgenesis to the prevalence of KAL1 gene defects in patients with sporadic Kallmann syndrome (KS).

DESIGN

Prospective assessment of renal structure and DNA sequence analysis of the KAL1 gene.

SETTING

Outpatient clinics of the divisions of endocrinology of university hospitals.

PATIENT(S)

Sixteen male patients with sporadic KS.

INTERVENTION(S)

Assessment of renal structure by abdominal ultrasounds scans and DNA extraction, polymerase chain reaction amplification, and DNA sequence analysis of all 14 exons of the KAL1 gene.

MAIN OUTCOME MEASURE(S)

KAL 1 gene structure and presence of renal dysgenesis.

RESULT(S)

Renal dysgenesis was identified in only two of 16 KS patients. Genetic defects were found in only two patients with KS, that is, in those with the identified renal dysgenesis. The first gene defect was identified in a patient with associated right renal agenesis who had two point mutations in the KAL1 gene: the first was a G to A transition in exon 11, turning codon 514 encoding glutamic acid into lysine; and the second was a G to A transition in exon 13, turning codon 660 encoding alanine into threonine. The second gene defect was identified in a patient with ichthyosis, right renal agenesis, and mirror movements of the upper limbs (synkinesia) and comprised a deletion of exons 5-10 of the KAL1 gene and a complete deletion of the steroid sulphatase gene.

CONCLUSION(S)

The phenotype of renal agenesis/dysgenesis strongly indicates the existence of KAL1 gene defects in the genotype of patients with sporadic KS, providing evidence for the X-linked mode of inheritance and offering the opportunity for genetic counseling.

Kallmann syndrome: fibroblast growth factor signaling insufficiency?

Kallmann syndrome (KAL) is a developmental disease that combines hypogonadotropic hypogonadism and anosmia. Anosmia is related to the absence or hypoplasia of the olfactory bulbs. Hypogonadism is due to GnRH deficiency and is likely to result from the failed embryonic migration of GnRH-synthesizing neurons. These cells normally migrate from the olfactory epithelium to the forebrain along the olfactory nerve pathway. KAL is phenotypically and genetically heterogeneous. The gene responsible for the X-chromosome linked form of the disease (KAL1) has been identified in 1991. KAL1 encodes anosmin-1, an approximately 95-kDa glycoprotein of unknown function which is present locally in various extracellular matrices during the period of organogenesis. The recent finding that FGFR1 mutations are involved in an autosomal dominant form of Kallmann syndrome (KAL2), combined with the analysis of mutant mouse embryos that no longer express Fgfr1 in the telencephalon, suggests that the disease results from a deficiency in FGF signaling at the earliest stage of olfactory bulb morphogenesis. We propose that the role of anosmin-1 is to enhance FGF signaling and suggest that the gender difference in anosmin-1 dose (because KAL1 partially escapes X-inactivation) explains the higher prevalence of the disease in males.

Renal abnormalities in patients with Kallmann syndrome

OBJECTIVE

To report experience in patients with Kallmann syndrome (KS) in whom urography was used to establish the type and frequency of renal anomalies associated with the disorder.

PATIENTS AND METHODS

Of 19 patients with KS, 15 had the X-linked recessive form of the disease, whereas the remaining four were sporadic. Each patient underwent intravenous pyelography (IVP) using a non-ionic, low osmolarity contrast medium.

RESULTS

Of the 19 patients with KS, 10 had kidney abnormalities; four presented with unilateral renal agenesis and six had less severe forms of renal abnormality (renal malrotation in four and bilateral dilatation of the calyces and pelves in two). One of the patients with unilateral renal agenesis carried a deletion in KAL, the gene responsible for the X-linked type of KS. Three of the four patients with renal malrotation had a confirmed X-linked recessive form and one carried a point mutation in KAL.

CONCLUSION

These results suggest that kidney abnormalities are more frequent and diverse in patients with KS than previously reported. They also indicate that defects in the KAL gene may contribute to abnormal renal development. However, a review of the literature revealed no close correlation between KAL mutations and kidney anomalies in the X-linked type of disease. Taken together, these data suggest that KAL mutations are not invariably associated with failure of renal development and that additional factors (epigenetic or local) may compensate for defects in the KAL protein.

Kallmann syndrome in a boy with a t(1;10) translocation detected by reverse chromosome painting

Prometaphase chromosomes from a 16 year old boy with hypogonadotrophic hypogonadism and anosmia (Kallmann syndrome) showed a tiny chromosome fragment attached to the long arm of one chromosome 1 without a visible reciprocal translocation chromosome. Chromosome painting with libraries from chromosomes 1 and X excluded a t(X;1) translocation, but failed to detect a second translocation chromosome. Through reverse chromosome painting, an unbalanced der(1), t(1;10) (q44;q26) translocation could be detected. This is the third case of Kallmann syndrome with a de novo rearrangement between two autosomes. The distal long arm of chromosome 1 may contain a candidate locus for a gene, mutations of which may cause the Kallmann phenotype; a 10q location seems less likely.

A molecular approach to the pathophysiology of the X chromosome-linked Kallmann's syndrome

The human KAL gene is responsible for the X chromosome-linked Kallmann's syndrome, which consists of an association between hypogonadotropic hypogonadism and anosmia (or hyposmia). Additional symptoms are occasionally observed. The olfactory defect is associated with hypoplasia of the olfactory bulbs and tracts. The hypogonadism may be due to a defect in the embryonic migratory process of GnRH-synthesizing neurones from the olfactory pits up to the brain. The human and chicken KAL genes have been isolated. From the amino acid sequences deduced, it has been postulated that the KAL protein is an extracellular matrix component, with putative antiprotease activity and adhesion function. Various point mutations and, in a few cases, deletions of KAL have been detected in patients. By in situ hybridization, KAL expression has been studied during embryonic development in the chick. From embryonic day 2 (ED2) to ED8, the KAL gene is expressed in various endodermal, mesodermal and ectodermal derivatives, whereas the expression from ED8 is almost entirely restricted to definite neuronal populations in the central nervous system, most of which still express the gene after hatching. According to such a spatiotemporal pattern of expression, we suggest that the KAL gene is involved both in morphogenetic events and in late neuronal differentiation and/or neuronal trophicity. With respect to the olfactory system, the KAL gene is expressed in the mitral cells of the olfactory bulbs from ED8 onwards. In contrast, no expression of the KAL gene is detected at any stage in either the embryonic olfactory epithelium or the surrounding nasal mesenchyme. Therefore, assuming that similar conditions are found in the human embryo, we suggest that the olfactory anomaly in X-linked Kallmann's syndrome results from a central target cell defect. Current hypotheses regarding the pathophysiology of the GnRH deficiency are also discussed. In situ hybridization experiments in the human embryo, as well as characterization of the KAL protein, are in progress.

Complex chromosomal rearrangements: some breakpoints may have cellular adaptive significance

Cytogenetic study of a 3-year-old girl with developmental delay and some minor abnormalities revealed a complex chromosome rearrangement (CCR) involving seven chromosomes with eight breakpoints, leading to monosomy of segment 5q15-q22. According to breakpoint distribution, CCRs may be classified as those with primary intrachromosomal abnormalities (including inversions, insertions, duplications, etc.) and those without them. Only the latter group of CCRs was used in this analysis. Comparison of theoretical and observed breakpoint distributions in 33 cases demonstrated that recurrent involvement of some chromosome(s) ("re-entry") occurs more frequently than expected. One possible explanation for this observation suggests that the initial event leads to an unstable provisional rearrangement, and subsequent breaks are necessary to stabilize the karyotype.