Luisa de Sanctis

Non-type I cystinuria caused by mutations in SLC7A9, encoding a subunit (b(o,+)AT) of rBAT

Cystinuria (MIM 220100) is a common recessive disorder of renal reabsorption of cystine and dibasic amino acids. Mutations in SLC3A1, encoding rBAT, cause cystinuria type I (ref. 1), but not other types of cystinuria (ref. 2). A gene whose mutation causes non-type I cystinuria has been mapped by linkage analysis to 19q12–13.1 (refs 3,4). We have identified a new transcript, encoding a protein (bo,+AT, for bo,+ amino acid transporter) belonging to a family of light subunits of amino acid transporters, expressed in kidney, liver, small intestine and placenta, and localized its gene (SLC7A9) to the non-type I cystinuria 19q locus. Co-transfection of bo,+AT and rBAT brings the latter to the plasma membrane, and results in the uptake of L-arginine in COS cells. We have found SLC7A9 mutations in Libyan-Jews, North American, Italian and Spanish non-type I cystinuria patients. The Libyan Jewish patients are homozygous for a founder missense mutation (V170M) that abolishes b o,+AT amino-acid uptake activity when co-transfected with rBAT in COS cells. We identified four missense mutations (G105R, A182T, G195R and G295R) and two frameshift (520insT and 596delTG) mutations in other patients. Our data establish that mutations in SLC7A9 cause non-type I cystinuria, and suggest that bo,+AT is the light subunit of rBAT.

SOX2 anophthalmia syndrome

Heterozygous, de novo, loss‐of‐function mutations in SOX2 have been shown to cause bilateral anophthalmia. Here we provide a detailed description of the clinical features associated with SOX2 mutations in the five individuals with reported mutations and four newly identified cases (including the first reported SOX2 missense mutation). The SOX2‐associated ocular malformations are variable in type, but most often bilateral and severe. Of the nine patients, six had bilateral anophthalmia and two had anophthalmia with contralateral microphthalmia with sclerocornea. The remaining case had anophthalmia with contralateral microphthalmia, posterior cortical cataract and a dysplastic optic disc, and was the only patient to have measurable visual acuity. The relatively consistent extraocular phenotype observed includes: learning disability, seizures, brain malformation, specific motor abnormalities, male genital tract malformations, mild facial dysmorphism, and postnatal growth failure. Identifying SOX2 mutations from large cohorts of patients with structural eye defects has delineated a new, clinically‐recognizable, multisystem disorder and has provided important insight into the developmental pathways critical for morphogenesis of the eye, brain, and male genital tract.

Molecular Analysis of the GNAS1 Gene for the Correct Diagnosis of Albright Hereditary Osteodystrophy and Pseudohypoparathyroidism

Pseudohypoparathyroidism (PHP) is a heterogeneous disease characterized by PTH resistance and classified as types Ia, Ib, Ic, and II, according to its different pathogenesis and phenotype. PHP-Ia patients show Gsα protein deficiency, PTH resistance, and typical Albright hereditary osteodystrophy (AHO). Heterozygous mutations in the GNAS1 gene encoding the Gsα protein have been identified both in PHP-Ia and in pseudopseudohypoparathyroidism (PPHP), a disorder with isolated AHO. A single GNAS1 mutation may be responsible for both PHP-Ia and PPHP in the same family when inherited from the maternal and the paternal allele, respectively, suggesting that GNAS1 is an imprinted gene. To evaluate whether molecular diagnosis is a useful tool to characterize AHO and PHP when testing for Gsα activity and PTH resistance is not available, we have performed GNAS1 mutational analysis in 43 patients with PTH resistance and/or AHO. Sequencing of the whole coding region of the GNAS1 gene identified 11 mutations in 18 PHP patients, eight of which have not been reported previously. Inheritance was ascertained in 13 cases, all of whom had PHP-Ia: the mutated alleles were inherited from the mothers, who had AHO (PPHP), consistent with the proposed imprinting mechanism. GNAS1 molecular analysis confirmed the diagnosis of PHP-Ia and PPHP in the mutated patients. Our results stress the usefulness of this approach to obtain a complete diagnosis, expand the GNAS1 mutation spectrum, and illustrate the wide mutation heterogeneity of PHP and PHP-Ia.

Molecular analysis of the cystinuria disease gene: identification of four new mutations, one large deletion, and one polymorphism

Abstract A cystinuria disease gene (rBAT) has recently been identified, but evidence strongly suggests that only Type-I cystinuria is due to mutations in this gene. Sixteen point mutations and a large deletion causing the disease have so far been described in the rBAT gene sequence. To identify new mutated alleles, genomic DNA was analyzed, after the determination of the entire genomic structure of the rBAT gene, by RNA-single strand conformation polymorphism analysis, an accurate and sensitive method able to detect nucleotide changes. Four new point mutations, a large deletion, and a common intragenic polymorphism were detected. These new mutations increase to 22 the number of mutated alleles so far characterized in rBAT. In addition, the frequency of 21 mutations was assessed in a sample of accurately defined Type-I cystinuria choromosomes. They account for about 58% of all Type-I chromosomes, mutation M467T being the most common (0.26).

Functional characterization of GNAS mutations found in patients with pseudohypoparathyroidism type Ic defines a new subgroup of pseudohypoparathyroidism affecting selectively Gsα-receptor interaction.

Pseudohypoparathyroidism type Ia (PHPIa) is caused by GNAS mutations leading to deficiency of the α‐subunit of stimulatory G proteins (Gsα) that mediate signal transduction of G protein‐coupled receptors via cAMP. PHP type Ic (PHPIc) and PHPIa share clinical features of Albright hereditary osteodystrophy (AHO); however, in vitro activity of solubilized Gsα protein is normal in PHPIc but reduced in PHPIa. We screened 32 patients classified as PHPIc for GNAS mutations and identified three mutations (p.E392K, p.E392X, p.L388R) in four unrelated families. These and one novel mutation associated with PHPIa (p.L388P) were introduced into a pcDNA3.1(−) expression vector encoding Gsα wild‐type and expressed in a Gsα‐null cell line (GnasE2−/E2−). To investigate receptor‐mediated cAMP accumulation, we stimulated the endogenous expressed β2‐adrenergic receptor, or the coexpressed PTH or TSH receptors, and measured the synthesized cAMP by RIA. The results were compared to receptor‐independent cholera toxin‐induced cAMP accumulation. Each of the mutants associated with PHPIc significantly reduced or completely disrupted receptor‐mediated activation, but displayed normal receptor‐independent activation. In contrast, PHPIa associated p.L388P disrupted both receptor‐mediated activation and receptor‐independent activation. We present a new subgroup of PHP that is caused by Gsα deficiency and selectively affects receptor coupling functions of Gsα. Hum Mutat 32:1–8, 2011.

Dihydropteridine reductase deficiency: Physical structure of the QDPR gene, identification of two new mutations and genotype–phenotype correlations

Dihydropteridine reductase (DHPR) is an enzyme involved in recycling of tetrahydrobiopterin (BH4), the cofactor of the aromatic amino acid hydroxylases. Its deficiency is characterized by hyperphenylalaninemia due to the secondary defect of phenylalanine hydroxylase and depletion of the neurotransmitters dopamine and serotonin, whose syntheses are controlled by tryptophan and tyrosine hydroxylases. The DHPR cDNA has been cloned and mapped on 4p15.3. In the present study we report the genomic structure of the DHPR gene (QDPR). This gene includes seven exons within a range of 84–564 bp; the corresponding introns are flanked by canonic splice junctions. We also present a panel of PCR primers complementary to intronic sequences that greatly facilitates amplification of the gene and provides a genomic DNA approach for mutation detection. We have used this approach to study six patients with DHPR deficiency. Four known mutations (G23D, H158Y, IVS5G + 1A, R221X) and two new mutations (Y150C and G218ins9bp) were found. The Y150C mutation was found in compound heterozygosity with G23D, a mutation always associated with a severe phenotype in homozygous patients. This patient has an intermediate phenotype (good response to monotherapy with BH4). The mutant enzyme for Y150C was expressed in an E. coli system. Comparison of its kinetic parameters with those of the G23D mutant enzyme showed that it is not as effective as the wild‐type enzyme, but is more active than the G23D mutant. This patients intermediate phenotype is thus due to the mild DHPR mutation Y150C. Correlations between genotypes and phenotypes were also found for the other mutations. Hum Mutat 12:267–273, 1998.

McCune-Albright syndrome in a boy may present with a monolateral macroorchidism as an early and isolated clinical manifestation.

Background: Testis enlargement in McCune-Albright syndrome (MAS) is generally bilateral and associated with clinical and biochemical manifestations of sexual precocity. Case Report: We describe for the first time an unreported clinical expression of MAS in a 4.6-year-old boy presenting with monolateral testis enlargement and no signs of sexual precocity or other clinical manifestations of MAS at the time of presenting with macroorchidism. Both testosterone and LHRH-stimulated gonadotropin levels were in the prepubertal range. Serum inhibin B was increased to a pubertal level indicating Sertoli cell activation. The histological and immunocytochemical evaluation of the enlarged testis revealed Sertoli cell hyperplasia with no mature Leydig cells. Mutation R201C of GNAS1 gene, classically responsible for MAS, was identified in DNA samples from the right testis biopsy and leukocytes. Conclusions: (a) MAS should be taken into consideration in the clinicopathological approach to a boy with monolateral macroorchidism; (b) testicular enlargement may be only the presenting clinical manifestation of MAS and is not necessarily linked to manifestations of peripheral precocious puberty; (c) testicular autonomous hyperfunction in MAS may be restricted to Sertoli cells, as also demonstrated previously by others.

Fetal alcohol syndrome: new perspectives for an ancient and underestimated problem

The knowledge of the dangers of alcohol consumption during pregnancy isn’t indeed a new issue, but the recent evidences of ethyl-glucuronide and ethyl-sulfate in meconium as novel biomarkers of prenatal ethanol exposure open new perspectives for the early diagnosis of the alcohol-related birth defects. This is crucial for a better developmental outcome of the affected patients and for preventing additional cases in at risk families. The fetal alcohol syndrome is not a single entity but represents the most severe form of a spectrum of disorders, including distinctive craniofacial alterations, stunted growth and behavioral abnormalities, caused by complex gene-environment interactions. FAS must always be a diagnosis of exclusion and have to be differentiated from many conditions caused by other embryotoxin agents and genetic syndromes that share some phenotypic features. Even if the first trimester is considered the most vulnerable period, nowadays is known that a fetal damage might occur throughout all gestation. Since ethanol consumption is constantly increasing among young women, a substantial amount of work has to be made to implement the knowledge on alcohol fetal effects among women of childbearing age; moreover, awareness and training among professionals in the health care system might play a critical role in the early diagnosis of these serious conditions.

Regulation of spermatogenesis in McCune–Albright syndrome: lessons from a 15-year follow-up.

CONTEXT McCune-Albright syndrome (MAS) is a disorder caused by a post-zygotic gain-of-function mutation in the gene encoding the Gs-alpha protein. Sexual precocity, common in girls, has been reported in only 15% of boys, and little is known on the long-term evolution of MAS in males. OBJECTIVE In a boy with MAS, we studied spermatogenesis, testis histology, and immunohistochemistry with the aim to shed light on seminiferous tubule activity. DESIGN A boy who presented at the age of 2.9 years with sexual precocity, monolateral macroorchidism, increased testosterone levels, and suppressed gonadotropins was followed up until the age of 18. RESULTS Throughout follow-up testicular asymmetry persisted and gonadotropin and testosterone pattern did not change. At the age of 18, inhibin B was undetectable while alpha-immunoreactive inhibin was within normal range. Anti-Mullerian hormone level was slightly subnormal. Sperm cells were 3,900,000 per ejaculate. Histology of both testes showed spermatogonia, spermatocytes, and, in some tubes, matured spermatozoa. Sertoli cells were markedly stained with anti-inhibin alpha-subunit antibody in both the testes. There was no immunostaining of Sertoli, Leydig, or germ cells with anti-betaA or anti-betaB antibody. MAS R201H mutation was identified in both the testes. CONCLUSION The 15-year follow-up in this boy with MAS demonstrated that autonomous testicular activation and gonadotropin suppression persisted over time. This provides an interesting model of active spermatogenesis despite long-term FSH suppression. It also suggests that FSH is needed for the full expression of the inhibin betaB-subunit gene, an expression previously reported in the germ and Leydig cells of normal adult subjects.

A series of mutations in the dihydropteridine reductase gene resulting in either abnormal RNA splicing or DHPR protein defects

Five novel mutations are described which result in the rare hyperphenylalaninemia DHPR‐deficiency. Three of these are located at different intron/exon boundaries within the DHPR gene, and disrupt the maturation of the DHPR transcript such that little full‐length mRNA can be detected by RT‐PCR. Each mutation alters a conserved nucleotide within the splice site consensus sequence, and results in the skipping of an exon and, in one case, the activation of an inappropriate splicing signal. Two further mutations are missense mutations resulting in a non‐conservative amino acid change within the DHPR protein (L14P and G17V) and are associated with a severe phenotype. Hum Mutat 13:503–504, 1999.