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Antoine Moya-Plana, Carine Villanueva, Ollivier Laccourreye, Pierre Bonfils and Nicolas de Roux

Objective

Isolated congenital anosmia (ICA) is a rare phenotype defined as absent recall of any olfactory sensations since birth and the absence of any disease known to cause anosmia. Although most cases of ICA are sporadic, reports of familial cases suggest a genetic cause. ICA due to olfactory bulb agenesis and associated to hypogonadotropic hypogonadism defines Kallmann syndrome (KS), in which several gene defects have been described. In KS families, the phenotype may be restricted to ICA. We therefore hypothesized that mutations in KS genes cause ICA in patients, even in the absence of family history of reproduction disorders.

Design and methods

In 25 patients with ICA and olfactory bulb agenesis, a detailed phenotype analysis was conducted and the coding sequences of KAL1, FGFR1, FGF8, PROKR2, and PROK2 were sequenced.

Results

Three PROKR2 mutations previously described in KS and one new PROK2 mutation were found. Investigation of the families showed incomplete penetrance of these mutations.

Conclusions

This study is the first to report genetic causes of ICA and indicates that KS genes must be screened in patients with ICA. It also confirms the considerable complexity of GNRH neuron development in humans.

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Selmen Wannes, Monique Elmaleh-Bergès, Dominique Simon, Delphine Zénaty, Laetitia Martinerie, Caroline Storey, Georges Gelwane, Anne Paulsen, Emmanuel Ecosse, Nicolas De Roux, Jean Claude Carel and Juliane Léger

Objective

Non-idiopathic CPP is caused by acquired or congenital hypothalamic lesions visible on MRI or is associated with various complex genetic and/or syndromic disorders. This study investigated the different types and prevalence of non-isolated CPP phenotypes.

Design and Methods

This observational cohort study included all patients identified as having non-idiopathic CPP in the database of a single academic pediatric care center over a period of 11.5 years. Patients were classified on the basis of MRI findings for the CNS as having either hypothalamic lesions or complex syndromic phenotypes without structural lesions of the hypothalamus.

Results

In total, 63 consecutive children (42 girls and 21 boys) with non-isolated CPP were identified. Diverse diseases were detected, and the hypothalamic lesions visible on MRI (n = 28, 45% of cases) included hamartomas (n = 17; either isolated or with an associated syndromic phenotype), optic gliomas (n = 8; with or without neurofibromatosis type 1), malformations (n = 3) with interhypothalamic adhesions (n = 2; isolated or associated with syndromic CNS midline abnormalities, such as optic nerve hypoplasia, ectopic posterior pituitary) or arachnoid cysts (n = 1). The patients with non-structural hypothalamic lesions (n = 35, 55% of cases) had narcolepsy (n = 9), RASopathies (n = 4), encephalopathy or autism spectrum disorders with or without chromosomal abnormalities (n = 15) and other complex syndromic disorders (n = 7).

Conclusion

Our findings suggest that a large proportion (55%) of patients with non-isolated probable non-idiopathic CPP may have complex disorders without structural hypothalamic lesions on MRI. Future studies should explore the pathophysiological relevance of the mechanisms underlying CPP in these disorders.

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Dominique Simon, Ibrahima Ba, Nancy Mekhail, Emmanuel Ecosse, Anne Paulsen, Delphine Zenaty, Muriel Houang, Monique Jesuran Perelroizen, Gian-Paolo de Filippo, Mariacarolina Salerno, Gilbert Simonin, Rachel Reynaud, Jean-Claude Carel, Juliane Léger and Nicolas de Roux

Context and objective

Idiopathic central precocious puberty (iCPP) is defined as early activation of the hypothalamic–pituitary–gonadal axis in the absence of identifiable central lesions. Mutations of the makorin RING finger 3 (MKRN3) gene are associated with iCPP. We aimed to assess the frequency of MKRN3 mutations in iCPP and to compare the phenotypes of patients with and without MKRN3 mutations.

Design

An observational study was carried out on patients recruited at pediatric hospitals in France and Italy. Forty-six index CPP cases were screened for mutations in the MKRN3 coding sequence: 28 index cases of familial cases and 18 cases did not report any familial history of CPP. The endocrine phenotype was compared between MKRN3 mutated and non-mutated patients.

Results

MKRN3 mutations were identified in one sporadic and 13 familial cases. We identified five new heterozygous missense mutations predicted to be deleterious for protein function and two frameshift mutations, one new and the other recurrent, predicted to result in truncated proteins. Age at puberty onset varied very little among patients with MKRN3 mutations and puberty occurred earlier in these patients than in those without MKRN3 mutations (6.0 years (5.4–6.0) vs 7.0 years (6.0–7.0), P=0.01).

Conclusions

MKRN3 mutations are common in familial iCPP. MKRN3 is one of the gatekeepers of the postnatal activation of the gonadotropic axis.