Congenital Hypogonadotropic Hypogonadism with Anosmia and Gorlin Features Caused by a PTCH1 Mutation Reveals a New Candidate Gene for Kallmann Syndrome.

BACKGROUND: Two loci (CHD7 and SOX10) underlying Kallmann syndrome (KS) were discovered through clinical and genetic analysis of CHARGE and Waardenburg syndromes, conditions that include congenital anosmia caused by olfactory bulb (CA/OBs) defects and congenital hypogonadotropic hypogonadism (CHH). We hypothesized that other candidate genes for KS could be discovered by analyzing rare syndromes presenting with these signs. Study Design, Size, Duration: We first investigated a family with Gorlin-Goltz syndrome (GGS) in which affected members exhibited clinical signs suggesting KS. Participants/Materials, Methods: Proband and family members underwent detailed clinical assessment. The proband received detailed neuroendocrine evaluation. Genetic analyses included sequencing the PTCH1 gene at diagnosis, followed by exome analyses of causative or candidate KS/CHH genes, in order to exclude contribution to the phenotypes of additional mutations. Exome analyses in additional 124 patients with KS/CHH probands with no additional GGS signs. RESULTS: The proband exhibited CA, absent OBs on magnetic resonance imaging, and had CHH with unilateral cryptorchidism, consistent with KS. Pulsatile Gonadotropin-releasing hormone (GnRH) therapy normalized serum gonadotropins and increased testosterone levels, supporting GnRH deficiency. Genetic studies revealed 3 affected family members harbor a novel mutation of PTCH1 (c.838G> T; p.Glu280*). This unreported nonsense deleterious mutation results in either a putative truncated Ptch1 protein or in an absence of translated Ptch1 protein related to nonsense mediated messenger RNA decay. This heterozygous mutation cosegregates in the pedigree with GGS and CA with OBs aplasia/hypoplasia and with CHH in the proband suggesting a genetic linkage and an autosomal dominant mode of inheritance. No pathogenic rare variants in other KS/CHH genes cosegregated with these phenotypes. In additional 124 KS/CHH patients, 3 additional heterozygous, rare missense variants were found and predicted in silico to be damaging: p.Ser1203Arg, p.Arg1192Ser, and p.Ile108Met. CONCLUSION: This family suggests that the 2 main signs of KS can be included in GGS associated with PTCH1 mutations. Our data combined with mice models suggest that PTCH1 could be a novel candidate gene for KS/CHH and reinforce the role of the Hedgehog signaling pathway in pathophysiology of KS and GnRH neuron migration.

Pathogenic mosaic variants in congenital hypogonadotropic hypogonadism.

PURPOSE: Congenital hypogonadotropic hypogonadism (CHH) is a rare disorder resulting in absent puberty and infertility. The genetic architecture is complex with multiple loci involved, variable expressivity, and incomplete penetrance. The majority of cases are sporadic, consistent with a disease affecting fertility. The current study aims to investigate mosaicism as a genetic mechanism for CHH, focusing on de novo rare variants in CHH genes. METHODS: We evaluated 60 trios for de novo rare sequencing variants (RSV) in known CHH genes using exome sequencing. Potential mosaicism was suspected among RSVs with altered allelic ratios and confirmed using customized ultradeep sequencing (UDS) in multiple tissues. RESULTS: Among the 60 trios, 10 probands harbored de novo pathogenic variants in CHH genes. Custom UDS demonstrated that three of these de novo variants were in fact postzygotic mosaicism-two in FGFR1 (p.Leu630Pro and p.Gly348Arg), and one in CHD7 (p.Arg2428*). Statistically significant variation across multiple tissues (DNA from blood, buccal, hair follicle, urine) confirmed their mosaic nature. CONCLUSIONS: We identified a significant number of de novo pathogenic variants in CHH of which a notable number (3/10) exhibited mosaicism. This report of postzygotic mosaicism in CHH patients provides valuable information for accurate genetic counseling.

Clinical Management of Congenital Hypogonadotropic Hypogonadism.

The initiation and maintenance of reproductive capacity in humans is dependent on pulsatile secretion of the hypothalamic hormone GnRH. Congenital hypogonadotropic hypogonadism (CHH) is a rare disorder that results from the failure of the normal episodic GnRH secretion, leading to delayed puberty and infertility. CHH can be associated with an absent sense of smell, also termed Kallmann syndrome, or with other anomalies. CHH is characterized by rich genetic heterogeneity, with mutations in >30 genes identified to date acting either alone or in combination. CHH can be challenging to diagnose, particularly in early adolescence where the clinical picture mirrors that of constitutional delay of growth and puberty. Timely diagnosis and treatment will induce puberty, leading to improved sexual, bone, metabolic, and psychological health. In most cases, patients require lifelong treatment, yet a notable portion of male patients (∼10% to 20%) exhibit a spontaneous recovery of their reproductive function. Finally, fertility can be induced with pulsatile GnRH treatment or gonadotropin regimens in most patients. In summary, this review is a comprehensive synthesis of the current literature available regarding the diagnosis, patient management, and genetic foundations of CHH relative to normal reproductive development.

Congenital hypogonadotropic hypogonadism and constitutional delay of growth and puberty have distinct genetic architectures.

OBJECTIVE: Congenital hypogonadotropic hypogonadism (CHH) and constitutional delay of growth and puberty (CDGP) represent rare and common forms of GnRH deficiency, respectively. Both CDGP and CHH present with delayed puberty, and the distinction between these two entities during early adolescence is challenging. More than 30 genes have been implicated in CHH, while the genetic basis of CDGP is poorly understood. DESIGN: We characterized and compared the genetic architectures of CHH and CDGP, to test the hypothesis of a shared genetic basis between these disorders. METHODS: Exome sequencing data were used to identify rare variants in known genes in CHH (n = 116), CDGP (n = 72) and control cohorts (n = 36 874 ExAC and n = 405 CoLaus). RESULTS: Mutations in at least one CHH gene were found in 51% of CHH probands, which is significantly higher than in CDGP (7%, P = 7.6 × 10-11) or controls (18%, P = 5.5 × 10-12). Similarly, oligogenicity (defined as mutations in more than one gene) was common in CHH patients (15%) relative to CDGP (1.4%, P = 0.002) and controls (2%, P = 6.4 × 10-7). CONCLUSIONS: Our data suggest that CDGP and CHH have distinct genetic profiles, and this finding may facilitate the differential diagnosis in patients presenting with delayed puberty.

DCC/NTN1 complex mutations in patients with congenital hypogonadotropic hypogonadism impair GnRH neuron development.

Congenital hypogonadotropic hypogonadism (CHH) is a rare genetic disease characterized by absent puberty and infertility due to GnRH deficiency, and is often associated with anosmia [Kallmann syndrome (KS)]. The genetic etiology of CHH is heterogeneous, and more than 30 genes have been implicated in approximately 50% of patients with CHH. We hypothesized that genes encoding axon-guidance proteins containing fibronectin type-III (FN3) domains (similar to ANOS1, the first gene associated with KS), are mutated in CHH. We performed whole-exome sequencing in a cohort of 133 CHH probands to test this hypothesis, and identified rare sequence variants (RSVs) in genes encoding for the FN3-domain encoding protein deleted in colorectal cancer (DCC) and its ligand Netrin-1 (NTN1). In vitro studies of these RSVs revealed altered intracellular signaling associated with defects in cell morphology, and confirmed five heterozygous DCC mutations in 6 probands-5 of which presented as KS. Two KS probands carry heterozygous mutations in both DCC and NTN1 consistent with oligogenic inheritance. Further, we show that Netrin-1 promotes migration in immortalized GnRH neurons (GN11 cells). This study implicates DCC and NTN1 mutations in the pathophysiology of CHH consistent with the role of these two genes in the ontogeny of GnRH neurons in mice.

ß-Klotho deficiency protects against obesity through a crosstalk between liver, microbiota, and brown adipose tissue.

ß-Klotho (encoded by Klb) is the obligate coreceptor mediating FGF21 and FGF15/19 signaling. Klb-/- mice are refractory to beneficial action of pharmacological FGF21 treatment including stimulation of glucose utilization and thermogenesis. Here, we investigated the energy homeostasis in Klb-/- mice on high-fat diet in order to better understand the consequences of abrogating both endogenous FGF15/19 and FGF21 signaling during caloric overload. Surprisingly, Klb-/- mice are resistant to diet-induced obesity (DIO) owing to enhanced energy expenditure and BAT activity. Klb-/- mice exhibited not only an increase but also a shift in bile acid (BA) composition featured by activation of the classical (neutral) BA synthesis pathway at the expense of the alternative (acidic) pathway. High hepatic production of cholic acid (CA) results in a large excess of microbiota-derived deoxycholic acid (DCA). DCA is specifically responsible for activating the TGR5 receptor that stimulates BAT thermogenic activity. In fact, combined gene deletion of Klb and Tgr5 or antibiotic treatment abrogating bacterial conversion of CA into DCA both abolish DIO resistance in Klb-/- mice. These results suggested that DIO resistance in Klb-/- mice is caused by high levels of DCA, signaling through the TGR5 receptor. These data also demonstrated that gut microbiota can regulate host thermogenesis via conversion of primary into secondary BA. Pharmacologic or nutritional approaches to selectively modulate BA composition may be a promising target for treating metabolic disorders.

Mutations in fibroblast growth factor receptor 1 cause Kallmann syndrome with a wide spectrum of reproductive phenotypes.

BACKGROUND: Kallmann's syndrome (KS) is a clinically and genetically heterogeneous disorder consisting of idiopathic hypogonadotropic hypogonadism (IHH) and anosmia. Mutations in KAL1 causing the X-linked form of KS have been identified in 10% of all KS patients and consistently result in a severe reproductive phenotype. KAL1 gene encodes for anosmin-1, a key protein involved in olfactory and GnRH neuronal migration through a putative interaction with FGFR1. Heterozygous mutations in the FGFR1 gene accompanied by a high frequency of cleft palate and other facial dysmorphisms were recently identified in 8% of a large KS cohort, yet the reproductive phenotype of KS patients harboring FGFR1 mutations has not been described. RESULTS: One hundred and fifty probands with KS (130 males and 20 females) were studied to determine the frequency and distribution of FGFR1 mutations and their detailed reproductive phenotypes. Fifteen heterozygous mutations in unrelated probands were identified. Twelve missense mutations (p.R78C, p.V102I, p.D224H, p.G237D, p.R254Q, p.V273M, p.E274G, p.Y339C, p.S346C, p.I538V, p.G703S and p.G703R) were distributed among the first, second and third immunoglobulin-like domains (D1-D3), as well as the tyrosine kinase domain (TKD). The mutations Y339C and S346C are located in exon 8B and code for the isoform FGFR1c. Additionally, two nonsense mutations (p.T585X and p.R622X) were documented in the TKD of the protein. A wide spectrum of reproductive function was observed among KS probands including: (1) a severe phenotype demonstrated by microphallus, cryptorchidism, no pubertal development, undetectable serum gonadotropins and low serum testosterone (T) and inhibin B; (2) partial pubertal development; (3) the fertile eunuch variant of IHH with normal testicular size and active spermatogenesis with a reversal of HH after T therapy. In addition, we found an even wider spectrum of reproductive function within pedigrees carrying an FGFR1 mutation ranging from IHH to delayed puberty to normal reproductive function (anosmia only or asymptomatic carriers). These observations strongly suggest a role for other genes that modify the phenotype of FGFR1 mutations. CONCLUSION: KS patients and family members carrying an FGFR1 mutation present a broad spectrum of pubertal development in contrast to the almost uniform severe clinical phenotype described in KS subjects with a KAL1 mutation. Additionally, this report implicates the isoform FGFR1c in the pathogenesis of KS.

Mutations in fibroblast growth factor receptor 1 cause both Kallmann syndrome and normosmic idiopathic hypogonadotropic hypogonadism.

Mutations in KAL1 and FGFR1 cause Kallmann syndrome (KS), whereas mutations in the GNRHR and GPR54 genes cause idiopathic hypogonadotropic hypogonadism with normal olfaction (nIHH). Mixed pedigrees containing both KS and nIHH have also been described; however, the genetic cause of these rare cases is unknown. We examined the FGFR1 gene in seven nIHH subjects who either belonged to a mixed pedigree (n = 5) or who had associated midline defects (n = 2). Heterozygous FGFR1 mutations were found in three of seven unrelated nIHH probands with normal MRI of the olfactory system: (i) G237S in an nIHH female and a KS brother; (ii) (P722H and N724K) in an nIHH male missing two teeth and his mother with isolated hyposmia; and (iii) Q680X in a nIHH male with cleft lip/palate and missing teeth, his brother with nIHH, and his father with delayed puberty. We show that these mutations lead to receptor loss-of-function. The Q680X leads to an inactive FGFR1, which lacks a major portion of the tyrosine kinase domain (TKD). The G237S mutation inhibits proper folding of D2 of the FGFR1 and likely leads to the loss of cell-surface expression of FGFR1. In contrast, the (P722H and N724K) double mutation causes structural perturbations in TKD, reducing the catalytic activity of TKD. We conclude that loss-of-function mutations in FGFR1 cause nIHH with normal MRI of the olfactory system. These mutations also account for some of the mixed pedigrees, thus challenging the current idea that KS and nIHH are distinct entities.

Biotin-responsive basal ganglia disease maps to 2q36.3 and is due to mutations in SLC19A3.

Biotin-responsive basal ganglia disease (BBGD) is a recessive disorder with childhood onset that presents as a subacute encephalopathy, with confusion, dysarthria, and dysphagia, and that progresses to severe cogwheel rigidity, dystonia, quadriparesis, and eventual death, if left untreated. BBGD symptoms disappear within a few days with the administration of high doses of biotin (5-10 mg/kg/d). On brain magnetic resonance imaging examination, patients display central bilateral necrosis in the head of the caudate, with complete or partial involvement of the putamen. All patients diagnosed to date are of Saudi, Syrian, or Yemeni ancestry, and all have consanguineous parents. Using linkage analysis in four families, we mapped the genetic defect near marker D2S2158 in 2q36.3 (LOD=5.9; theta=0.0) to a minimum candidate region (approximately 2 Mb) between D2S2354 and D2S1256, on the basis of complete homozygosity. In this segment, each family displayed one of two different missense mutations that altered the coding sequence of SLC19A3, the gene for a transporter related to the reduced-folate (encoded by SLC19A1) and thiamin (encoded by SLC19A2) transporters.

Reversible kallmann syndrome, delayed puberty, and isolated anosmia occurring in a single family with a mutation in the fibroblast growth factor receptor 1 gene.

Kallmann syndrome (KS) is a clinically and genetically heterogeneous disorder. Recently, loss-of-function mutations in the fibroblast growth factor receptor 1 (FGFR1) gene have been shown to cause autosomal dominant KS. To date, the detailed reproductive phenotype of KS associated with mutations in the FGFR1 has yet to be described. We report a kindred comprising a male proband with KS and spontaneous reversibility, whose mother had delayed puberty and whose maternal grandfather isolated anosmia. The proband presented at age 18 yr with KS and was subsequently treated with testosterone (T) therapy. Upon discontinuation of T therapy, he recovered from his hypogonadotropic hypogonadism, as evidenced by a normal LH secretion pattern, sustained normal serum T levels, and active spermatogenesis. The three members of this single family harbor the same FGFR1 mutation (Arg(622)X) in the tyrosine kinase domain. This report demonstrates 1) the first genetic cause of the rare variant of reversible KS, 2) the reversal of hypogonadotropic hypogonadism in a proband carrying an FGFR1 mutation suggests a role of FGFR1 beyond embryonic GnRH neuron migration, and 3) a loss of function mutation in the FGFR1 gene causing delayed puberty.

Characterization of the human nasal embryonic LHRH factor gene, NELF, and a mutation screening among 65 patients with idiopathic hypogonadotropic hypogonadism (IHH).

As the mouse nasal embryonic LHRH factor gene (Nelf) encodes a guidance molecule for the migration of the olfactory axon and gonadotropin-releasing hormone neurons, its human homolog, NELF, is a candidate gene for Kallmann syndrome, a disease of idiopathic hypogonadotropic hypogonadism (IHH) with anosmia or hyposmia. We report here characterization of NELF and results of mutation analysis in 65 IHH patients. Assembling EST clones, RACE, and sequencing showed that NELF mapped to 9q34.3 is composed of 16 exons and 15 introns with a 1,590-bp ORF encoding 530 amino acids. RT-PCR on a fetal brain cDNA library revealed five alternatively spliced variants. Among them, NELF-v1 has 93-94% identity at the amino acid level to mouse/rat Nelf, and four other transcripts are also highly conserved among the three species. A 3.0-kb transcript is expressed most highly in the adult and fetal brain, testis, and kidney, indicating that NELF plays a role in the function of these tissues. Mutation screening detected in a patient with IHH one novel heterozygous missense mutation (1438A>G, T480A) at the donor-splice site in exon 15 of NELF. As this mutation was not found in 100 normal control individuals, T480A may be associated with IHH. Four other novel SNPs (102C > T and 1029C > T within the coding region, and two IVS14+47C > T and IVS15+41G > A) were also identified in NELF.

GNRHR mutations in a woman with idiopathic hypogonadotropic hypogonadism highlight the differential sensitivity of luteinizing hormone and follicle-stimulating hormone to gonadotropin-releasing hormone.

Mutations in the GnRH receptor gene (GNRHR) are a cause of idiopathic hypogonadotropic hypogonadism. We describe a normosmic female subject with congenital idiopathic hypogonadotropic hypogonadism in whom treatment with pulsatile GnRH resulted in an unusual response. The subject not only required an increased dose of pulsatile GnRH for ovarian follicular development, but LH secretion did not increase appropriately, estradiol levels remained low, and she did not ovulate spontaneously. Sequencing of the GNRHR coding sequence revealed compound heterozygous mutations leading to amino acid substitutions [N10K+Q11K] and P320L. The introduction of the P320L mutation into the GnRH receptor led to failure of detectable ligand binding and failure of stimulation of inositol phosphate production and gonadotropin subunit gene promoter activity in response to GnRH in transiently transfected cells. The [N10K+Q11K] mutation resulted in reduced binding of a GnRH agonist to 25% of the wild-type receptor. In addition, the EC(50) value for GnRH stimulation of inositol phosphate production was significantly increased, and the dose-response curves for stimulation of alpha gonadotropin subunit, LHbeta, and FSHbeta gene transcription by GnRH were similarly shifted to the right. Stimulation of FSHbeta gene transcription was more sensitive to GnRH than LHbeta for both wild-type and [N10K+Q11K] GnRH receptors, resulting in a greater loss of LHbeta stimulation than FSHbeta by the [N10K+Q11K] mutant at any given submaximal GnRH concentration. We propose that the mutations in the GnRH receptor result in a rightward shift of the dose-response curves of gonadotropin responses to pulsatile GnRH in the subject and unmask the differential sensitivities of LH and FSH to GnRH, resulting in low LH and estradiol levels despite appropriate FSH secretion and follicular growth.

The GPR54 gene as a regulator of puberty.

BACKGROUND: Puberty, a complex biologic process involving sexual development, accelerated linear growth, and adrenal maturation, is initiated when gonadotropin-releasing hormone begins to be secreted by the hypothalamus. We conducted studies in humans and mice to identify the genetic factors that determine the onset of puberty. METHODS: We used complementary genetic approaches in humans and in mice. A consanguineous family with members who lacked pubertal development (idiopathic hypogonadotropic hypogonadism) was examined for mutations in a candidate gene, GPR54, which encodes a G protein-coupled receptor. Functional differences between wild-type and mutant GPR54 were examined in vitro. In parallel, a Gpr54-deficient mouse model was created and phenotyped. Responsiveness to exogenous gonadotropin-releasing hormone was assessed in both the humans and the mice. RESULTS: Affected patients in the index pedigree were homozygous for an L148S mutation in GPR54, and an unrelated proband with idiopathic hypogonadotropic hypogonadism was determined to have two separate mutations, R331X and X399R. The in vitro transfection of COS-7 cells with mutant constructs demonstrated a significantly decreased accumulation of inositol phosphate. The patient carrying the compound heterozygous mutations (R331X and X399R) had attenuated secretion of endogenous gonadotropin-releasing hormone and a left-shifted dose-response curve for gonadotropin-releasing hormone as compared with six patients who had idiopathic hypogonadotropic hypogonadism without GPR54 mutations. The Gpr54-deficient mice had isolated hypogonadotropic hypogonadism (small testes in male mice and a delay in vaginal opening and an absence of follicular maturation in female mice), but they showed responsiveness to both exogenous gonadotropins and gonadotropin-releasing hormone and had normal levels of gonadotropin-releasing hormone in the hypothalamus. CONCLUSIONS: Mutations in GPR54, a G protein-coupled receptor gene, cause autosomal recessive idiopathic hypogonadotropic hypogonadism in humans and mice, suggesting that this receptor is essential for normal gonadotropin-releasing hormone physiology and for puberty.

Autosomal recessive idiopathic hypogonadotropic hypogonadism: genetic analysis excludes mutations in the gonadotropin-releasing hormone (GnRH) and GnRH receptor genes.

Failure of the normal pattern of episodic secretion of GnRH from the hypothalamus results in the clinical syndrome of idiopathic hypogonadotropic hypogonadism (IHH), with failure of pubertal development and infertility. The only gene that has been implicated in normosmic IHH is the GnRH receptor gene (GNRHR), which accounts for 10% of cases. This report presents four families with autosomal recessive IHH, including a consanguineous pedigree from the Middle East. Defects within the genomic coding sequence of the GNRHR, and the GnRH gene itself, GNRH1, were excluded by temperature gradient gel electrophoresis, direct sequencing, and haplotypes created from simple sequence polymorphisms flanking the GNRH1 and GNRHR loci. We concluded that: 1) genetic analysis has excluded sequence variations in GNRH1 and GNRHR in four families with recessive IHH, suggesting the existence of a novel, as-yet-undiscovered gene for this condition, and 2) because mutation analysis of genomic coding sequence will fail to detect mutations deep within introns or regulatory regions, haplotype analysis is the preferred genetic methodology to eliminate the role of specific candidate genes.

A locus for autosomal recessive idiopathic hypogonadotropic hypogonadism on chromosome 19p13.3.

Idiopathic hypogonadotropic hypogonadism (IHH) is traditionally established by 1) the absence of spontaneous pubertal development by age 18 yr and 2) low sex steroids with inappropriately low gonadotropins in the absence of any functional or anatomic cause. To identify a novel disease locus for IHH, a genome wide scan was performed on a large, consanguineous Saudi family with 6 affected individuals. Linkage over a 1.06 Mb interval on chromosome 19p13.3 was established with a maximal two point LOD score of 5.17. Because numerous genes and hypothetical proteins are mapped to this region, further studies will be necessary to determine the precise genetic defect in this family.

A locus for autosomal dominant mitral valve prolapse on chromosome 11p15.4.

Mitral valve prolapse (MVP) is a common cardiovascular abnormality in the United States, occurring in approximately 2.4% of the general population. Clinically, patients with MVP exhibit fibromyxomatous changes in one or both of the mitral leaflets that result in superior displacement of the leaflets into the left atrium. Although often clinically benign, MVP can be associated with important accompanying sequelae, including mitral regurgitation, bacterial endocarditis, congestive heart failure, atrial fibrillation, and even sudden death. MVP is genetically heterogeneous and is inherited as an autosomal dominant trait that exhibits both sex- and age-dependent penetrance. In this report, we describe the results of a genome scan and show that a locus for MVP maps to chromosome 11p15.4. Multipoint parametric analysis performed by use of GENEHUNTER gave a maximum LOD score of 3.12 for the chromosomal region immediately surrounding the four-marker haplotype D11S4124-D11S2349-D11S1338-D11S1323, and multipoint nonparametric analysis (NPL) confirms this finding (NPL=38.59; P=.000397). Haplotype analysis across this region defines a 4.3-cM region between the markers D11S1923 and D11S1331 as the location of a new MVP locus, MMVP2, and confirms the genetic heterogeneity of this disorder. The discovery of genes involved in the pathogenesis of this common disease is crucial to understanding the marked variability in disease expression and mortality seen in MVP.

Hypogonadotropic hypogonadism and cerebellar ataxia: detailed phenotypic characterization of a large, extended kindred.

Although the co-occurrence of cerebellar ataxia and hypogonadism has been recognized for close to 100 yr, cases of Gordon Holmes syndrome are quite rare. This report describes the largest kindred characterized to date. The parents of the three affected siblings are first cousins, suggesting that the disease was inherited as an autosomal recessive trait. The siblings' initial evaluation was notable for low serum levels of sex steroids and gonadotropins (consistent with hypogonadotropic hypogonadism), progressive ataxia, and dementia. Extended treatment with physiological doses of pulsatile GnRH failed to stimulate a gonadotropin response. Brain imaging revealed volume loss in the cerebellum, with extensive abnormalities in the cerebral white matter. This unique family suggests that a common genetic mechanism is responsible for the syndrome of progressive hypogonadotropism and cerebellar ataxia.

Cloning and characterization of the mouse Mcoln1 gene reveals an alternatively spliced transcript not seen in humans.

BACKGROUND: Mucolipidosis type IV (MLIV) is an autosomal recessive lysosomal storage disorder characterized by severe neurologic and ophthalmologic abnormalities. Recently the MLIV gene, MCOLN1, has been identified as a new member of the transient receptor potential (TRP) cation channel superfamily. Here we report the cloning and characterization of the mouse homologue, Mcoln1, and report a novel splice variant that is not seen in humans. RESULTS: The human and mouse genes display a high degree of synteny. Mcoln1 shows 91% amino acid and 86% nucleotide identity to MCOLN1. Also, Mcoln1 maps to chromosome 8 and contains an open reading frame of 580 amino acids, with a transcript length of approximately 2 kb encoded by 14 exons, similar to its human counterpart. The transcript that results from murine specific alternative splicing encodes a 611 amino acid protein that differs at the c-terminus. CONCLUSIONS: Mcoln1 is highly similar to MCOLN1, especially in the transmembrane domains and ion pore region. Also, the late endosomal/lysosomal targeting signal is conserved, supporting the hypothesis that the protein is localized to these vesicle membranes. To date, there are very few reports describing species-specific splice variants. While identification of Mcoln1 is crucial to the development of mouse models for MLIV, the fact that there are two transcripts in mice suggests an additional or alternate function of the gene that may complicate phenotypic assessment.