L De Sanctis

New insights into cystinuria: 40 new mutations, genotype–phenotype correlation, and digenic inheritance causing partial phenotype

Objective: To clarify the genotype–phenotype correlation and elucidate the role of digenic inheritance in cystinuria. Methods: 164 probands from the International Cystinuria Consortium were screened for mutations in SLC3A1 (type A) and SLC7A9 (type B) and classified on the basis of urine excretion of cystine and dibasic amino acids by obligate heterozygotes into 37 type I (silent heterozygotes), 46 type non-I (hyperexcretor heterozygotes), 14 mixed, and 67 untyped probands. Results: Mutations were identified in 97% of the probands, representing 282 alleles (86.8%). Forty new mutations were identified: 24 in SLC3A1 and 16 in SLC7A9. Type A heterozygotes showed phenotype I, but mutation DupE5-E9 showed phenotype non-I in some heterozygotes. Type B heterozygotes showed phenotype non-I, with the exception of 10 type B mutations which showed phenotype I in some heterozygotes. Thus most type I probands carried type A mutations and all type non-I probands carried type B mutations. Types B and A mutations contributed to mixed type, BB being the most representative genotype. Two mixed cystinuria families transmitted mutations in both genes: double compound heterozygotes (type AB) had greater aminoaciduria than single heterozygotes in their family. Conclusions: Digenic inheritance is an exception (two of 164 families), with a limited contribution to the aminoaciduria values (partial phenotype) in cystinuria. Further mutational analysis could focus on one of the two genes (SLC3A1 preferentially for type I and SLC7A9 for type non-I probands), while for mixed probands analysis of both genes might be required, with priority given to SLC7A9.

Genetics of McCune-Albright syndrome

McCune-Albright syndrome (MAS) is a rare proteiform disease due to postzygotic, somatic mutations at codon R201 of the GNAS1 gene that results in cellular mosaicism. Different methods have been used in the molecular analysis of DNA samples from several tissues of patients with one or more MAS signs, with various mutation detection rates. We review data from the literature to investigate whether patient inclusion criteria for GNAS1 analysis, the molecular methods used to search for R201 mutations, and the type of tissues analysed, can influence the mutation detection rate in MAS. Our study indicates that to overcome the problems related to GNAS1 analysis in MAS, sensitive and specific molecular methods must be used to look for the mutation from all available affected tissues and from easily accessible tissues, and even more so in the presence of atypical and monosymptomatic forms of MAS.

Thyroid abnormalities in children and adolescents with mccune-albright syndrome

Background: To date, there is no agreement about the frequency or the features of thyroid abnormalities in McCune-Albright syndrome (MAS). The aim of our study was to detect thyroid abnormalities in a cohort of MAS children and adolescents and to give indications for their treatment and follow-up. Methods: In 36 patients, 22 females and 14 males, thyroid function and sonographic features of thyroid were evaluated every 6–12 months. Results: Three males and 1 female had hyperthyroidism: 2 with nodular, 2 with diffuse goiters. They were treated with methimazole (0.2–0.5 mg/kg/day) with good clinical and biochemical responses. The remaining 32 patients were euthyroid, even if 7 displayed sonographic alterations, of whom 5 had nodular goiter with nodules >1 cm, and 2 micronodular goiter. Fine-needle aspiration biopsy was performed in 2 patients with nodules >1 cm, 1 showing hemorrhagic nodule and 1 colloid cystic nodule. Conclusions: Prevalence of thyroid alterations in the studied MAS series was 31%. 64% of 11 patients with thyroid alterations had nodular goiters, with nodules >1 cm. As the onset of thyroid disease ranged from 1 to 20 years, a strict monitoring of thyroid function is recommended every 6 months. Satisfactory treatment can be obtained and maintained with antithyroid drugs.

GH secretion in a cohort of children with pseudohypoparathyroidism type Ia.

Pseudohypoparathyroidism type Ia (PHP-Ia) is characterized by Albright’s hereditary osteodistrophy (AHO) and resistance to hormones that act via the α subunit of the Gs protein (Gsα) protein, ie PTH, TSH, FSH/LH, and, as recently described in limited series, GHRH. However, the current lack of data on GHRH secretion, obesity and short stature included in the AHO phenotype hampers interpretation of GH secretory status and its effects on these subjects. We evaluated GH secretion after GHRH plus arginine (Arg) stimulus, IGF-I levels and anthropometric features in an exclusively pediatric population of 10 PHP-Ia subjects. Of our PHP-Ia children, 5 out of 10 (50%) showed impaired GH responsiveness to the provocative test, with a lower prevalence than the 75–100% previously reported. A negative correlation (p=0.024) was found between GH secretion and body mass index (BMI), whereas no correlation emerged between GH and IGF-I values (p=0.948). Height and growth velocity did not significantly differ between GH-deficient and GH-sufficient subjects. In the 5 GH-deficient patients, GHRH resistance could arguably be responsible for hormonal impairment; however, 3 of them were obese, showing normal stature and IGF-I levels: the increased BMI in these subjects could influence GH secretion and its effects. In conclusion, GH deficiency is frequent among PHP-Ia children and its prevalence is variable, two factors indicating that GH secretory testing should be part of the routine management of this patient group. It could be argued that GHRH resistance is the pathogenetic mechanism in most patients, but further studies on GHRH secretion are needed to define which values can be considered as raised. Lastly, because BMI has been indicated as a major determinant of evoked adult GH response to provocative testing, GH levels related to increased BMI also in childhood could be helpful in defining GH assessment in obese or overweight PHP-Ia children.

McCune-Albright syndrome: persistence of autonomous ovarian hyperfunction during adolescence and early adult age.

Gonadal hyperfunction is the most frequent endocrine dysfunction in females with McCune-Albright syndrome (MAS). Peripheral precocious puberty is usually the first MAS manifestation in children, characterized by episodes of hypersecretion of estrogens with a consequent reduction in gonadotropin secretion. Little is known about the course of this endocrine disease in adolescence and during young adult life. The aim of this study was to evaluate ovarian function in 10 females with MAS (age 11.4-20.1 years) to detect the persistence of autonomous ovarian hyperfunction throughout and following adolescence, after at least 1 year wash out of any treatment for precocious puberty. LH, FSH, estradiol, prolactin, androgen secretion, ovarian and breast sonography in luteal and follicular phases of some menstrual cycles were evaluated. We demonstrated the persistence of some ovarian autonomy, documented by hyperestrogenism and/or low or absent gonadotropin secretion and/or ovarian cysts.

Mutations in TAZ/WWTR1, a co-activator of NKX2.1 and PAX8 are not a frequent cause of thyroid dysgenesis

Aim: In 80–85% of cases, congenital hypothyroidism is associated with thyroid dysgenesis (TD), but only in a small percentage of cases mutations in thyroid transcription factors (NKX2.1, PAX8, FOXE1, and NKX2.5) have been associated with the disease. Several studies demonstrated that the activity of the transcription factors can be modulated by the interaction with other proteins, such as coactivators and co-repressors, and TAZ (transcriptional co-activator with PDZ-binding motif or VVWTR1) is a co-activator interacting with both NKX2.1 and PAX8. In the present study we investigate the role of TAZ in the pathogenesis of TD. Material and methods: By Single Stranded Conformational Polymorphism, we screened the entire TAZ coding sequence for mutations in 96 patients with TD and in 96 normal controls. Results: No mutations were found in patients and controls, but we found several polymorphisms in both groups. No significant differences could be demonstrated in the prevalence of the mutations between patients and controls. Conclusions: Our data indicate that TAZ mutations are not a cause of TD in the series of patients studied.

GROWTH HORMONE TREATMENT IN IRRADIATED CHILDREN WITH BRAIN TUMORS

We assessed the efficacy of GH treatment in 25 GH deficient patients irradiated for brain tumors (eight with glioma cranio-irradiated, eleven with medulloblastoma and six with ependymoma craniospinal-irradiated). We administered GH at doses of 0.6-0.9 IU/kg/week for one to three years at least two years after diagnosis of the tumor. We assessed the efficacy of the treatment each year by comparing the values of height velocity over bone age and change in the ratios progression of chronological age/progression of bone age and progression of statural age/progression of bone age. The treatment promoted satisfactory growth; better results were obtained in patients with glioma, who received cranial irradiation only, than in those with medulloblastoma or ependymoma, who received spinal irradiation as well. Moreover, the growth prognosis improved, especially in the cranio-irradiated patients. In our series of patients four presented tumor recurrence; these results did not differ significantly from those in irradiated patients with cerebral tumors who were not treated with GH.

Genotype–phenotype correlation in dihydropteridine reductase deficiency

Inherited deficiency of dihydropteridine reductase (DHPR, EC 1.66.99.7) impairs the regeneration of tetrahydrobiopterin (BH 4 ), the essential cofactor of phenylalanine (Phe) (PAH, EC 1.14.16.1), tyrosine (Tyr) (TYH, EC 1.14.16.2) and tryptophan (Trp) (TRH, EC 1.14.16.4) hydroxylases, which is oxidized to qBH 2 during a coupled reaction with these enzymes. The main metabolic derangements caused by DHPR deficiency (McKusick 261630) are hyperphenylalaninaemia and impaired production of monoamine neurotransmitters derived from Tyr and Trp dopamine, noradrenaline and serotonin. Untreated patients can early develop a severe and progressive neurological picture (Blau et al 1996a). The control of hyperphenylalaninaemia and biogenic amine deficiency is necessary to improve their prognosis, together with folinic acid supplementation to avoid folate depletion (Spada et al 1996). However, in some DHPR patients a milder phenotype has been described characterized by absent neurological signs. These patients respond to a BH 4 monotherapy or do not require any treatment (Blau et al 1992). The DHPR gene (QDPR), on 4p15.3, includes seven exons (Dianzani et al 1998). It encodes for a protein of 244 amino acids, active as a homodimer. So far, 21 mutations have been described in QDPR uniformly scattered throughout the coding region (Dianzani et al 1998; Smooker et al 1999), with different mutations having different effects on the protein, as determined by in vitro studies (Smooker et al 1993; Zhang et al 1996). Most mutations have been found in single chromosomes. So far, only five of them have been identified more than once (de Sanctis et al 1996). In the present study we evaluated genotype-phenotype correlation in 21 completely characterized DHPR patients. Molecular, biochemical and clinical data on DHPR-deficient patients are stored in the BIOMDB and BIODEF database (Blau et al 1996b).

Laparoscopic management of ovarian cysts in peripheral precocious puberty of McCune-Albright syndrome

Ovarian cysts are common in peripheral precocious puberty in McCune-Albright syndrome (MAS). The clinical course of these cysts is unpredictable due to episodes of hyperestrogenism typical of MAS ovarian hyperfunction. In persistent and recurrent large ovarian cysts with sustained estrogen hypersecretion and relevant clinical disturbances (increased linear growth and bone age maturation, vaginal bleeding and psychological disturbances) treatment is mandatory. Experimental courses of estrogen-blocking drugs may have insufficient or nil therapeutic effects. In these cases and when molecular analysis is required to obtain MAS diagnosis as in isolated peripheral precocious puberty, surgery is the option. Laparoscopy minimizes surgical aggression and facilitates obtaining tissue samples for molecular analysis, and sometimes relieves hyperestrogenism with the excision of hyperactive ovarian areas. It can be conducted with trans-umbilical laparoscopic ovarian cystectomy (TULOC) before 3 years of age and with traditional techniques afterwards.

Phenotype characterization and prevalence of rBAT M467T mutation in Italian cystinuric patients

Cystinuria (McKusick 220100) is an inherited disorder affecting the transport of cystine (Cys) and dibasic amino acids arginine (Arg), lysine (Lys) and ornithine (Orn) in the epithelial cells of both jejunum and proximal convoluted tubule, with an overall prevalence of 1 :7000. The only relevant consequence at clinical level is the urolithiasis due to the low solubility of Cys and the complications caused by renal stone disease. The occurrence of at least three distinct clinical types of cystinuria raises the question whether cystinuria is a single disease or a group of different conditions with impaired amino acid transport. Recently, a gene encoding a Cys and dibasic amino acid transporter (rBAT) has been identified (Bertran et al 1993) and several mutations in this gene have been found in cystinuric patients (Gasparini et al 1995). One mutation, M467T, was found to be prevalent in the Spanish population (40%) (Calonge et al 1994). The aim of this study was to analyse the phenotype distribution and the prevalence of rBAT M467T mutation in Italian cystinuric patients.