Genetic characterization of a large cohort of Argentine 21-hydroxylase Deficiency

CONTEXT

21-hydroxylase deficiency is the most common cause of Congenital Adrenal Hyperplasia. It presents as severe or classical forms-salt wasting and simple virilizing-and a mild or nonclassical (NC). Several studies have reported the frequency of pathogenic variants in different populations, although few of them included a large number of NC patients.

OBJECTIVE

To analyse the CYP21A2 gene defects in a large cohort of Argentine patients.

DESIGN

Molecular characterization of 628 patients (168 classical, 460 nonclassical, representing 1203 nonrelated alleles), 398 relatives, 126 partners.

METHODS

Genetic variants were assessed by allele-specific PCR, PCR-RFLP or direct sequencing. Deletions, duplications and large gene conversions (LGC) were studied by Southern blot/MLPA or long-range PCR. Biological implications of novel variants were analysed by structure-based in silico studies.

RESULTS

The most frequent pathogenic variants were p.V282L (58%) in NC alleles and c.293-13C>G (31.8%) and p.I173N (21.1%) in classical. Deletions and LGC were found at low frequency (6.2%), 57 alleles had rare pathogenic variants, and 3 had novel variants: p.(S166F); p.(P189R), p.(R436L). Genotype-phenotype correlation was observed in 98.6% of the cases, 11 asymptomatic first-degree relatives had pathogenic variants in both alleles, and 21/126 partners were carriers.

CONCLUSIONS

We conducted a comprehensive genetic characterization of the largest cohort of 21-hydroxylase patients from the region. In particular, we add to the molecular characterization of a large number of NC patients and to the estimation of the disease carrier's frequency in our population.

Functional studies of p.R132C, p.R149C, p.M283V, p.E431K, and a novel c.652-2A>G mutations of the CYP21A2 gene

Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency is the most frequent inborn error of metabolism and accounts for 90–95% of CAH cases. In the present work, we analyzed the functional consequence of four novel previously reported point CYP21A2 mutations -p.R132C, p.R149C, p.M283V, p.E431K- found in Argentinean 21-hydroxylase deficient patients. In addition, we report an acceptor splice site novel point mutation, c.652-2A>G, found in a classical patient in compound heterozygosity with the rare p.R483Q mutation. We performed bioinformatic and functional assays to evaluate the biological implication of the novel mutation. Our analyses revealed that the residual enzymatic activity of the isolated mutants coding for CYP21A2 aminoacidic substitutions was reduced to a lesser than 50% of the wild type with both progesterone and 17-OH progesterone as substrates. Accordingly, all the variants would predict mild non-classical alleles. In one non-classical patient, the p.E431K mutation was found in cis with the p.D322G one. The highest decrease in enzyme activity was obtained when both mutations were assayed in the same construction, with a residual activity most likely related to the simple virilizing form of the disease. For the c.652-2A>G mutation, bioinformatic tools predicted the putative use of two different cryptic splicing sites. Nevertheless, functional analyses revealed the use of only one cryptic splice acceptor site located within exon 6, leading to the appearance of an mRNA with a 16 nt deletion. A severe allele is strongly suggested due to the presence of a premature stop codon in the protein only 12 nt downstream.

[Pediatric emergency: adrenal insufficiency and adrenal crisis]

Adrenal insufficiency is defined by impaired secretion of adrenocortical hormones. It is classified upon the etiology in primary and secondary. Rapid recognition and therapy of adrenocortical crisis are critical to survival. Patients often have nonspecific symptoms: anorexia, vomiting, weakness, fatigue and lethargy. They are followed by hypotension, shock, hypoglicemia, hyponatremia and hyperkalemia. All patients with adrenal insufficiency require urgent fluid reposition, correction of hypoglycemia and glucocorticoid replacement, in order to avoid serious consequences of adrenal crisis. After initial crisis treatment, maintenance dose of corticoids should be indicated. Mineralocorticoids replacement, if necessary, should also be initiated.

Classical and nonclassical 21-hydroxylase deficiency: a molecular study of Argentine patients

OBJECTIVE

To characterize the molecular basis of the 21-hydroxylase deficiency in a group of Argentine patients presenting the classical and nonclassical forms of the disease.

DESIGN

To analyse the frequency of point mutations in the CYP21 gene by DNA amplification and mutation detection.

PATIENTS

Forty-one patients from 36 nonrelated families: 25 nonclassical (NC), 11 salt-wasting (SW) and five simple virilizing (SV). A total of 27 parents and 13 nonaffected siblings were also analysed.

MEASUREMENTS

Basal steroid hormones and 17-hydroxyprogesterone levels following adrenal stimulation with adrenocorticotrophic hormone were measured, together with an analysis of 10 point mutations in the CYP21 gene.

RESULTS

A total of 83% and 74.4% classical and nonclassical chromosomes, respectively, were characterized. The intron 2 mutation was the most prevalent among classical alleles. In addition, a high frequency for R356W was observed in both groups (13.3 and 6.9%, respectively), while V281L was the most frequent mutation among the nonclassical patients with a frequency of 39.5%. No alleles containing P30L were observed, and one de novo mutation (R356W) was found. A total of 68.3% patients were fully genotyped, and all but one showed no genotype/phenotype discrepancy. Though the cut-off value for post-ACTH 17-hydroxyprogesterone stimulation was 30.25 nmol/l (10.00 microg/l), the lowest value observed in the fully genotyped nonclassical group was 42.35 nmol/l (14.00 microg/l).

CONCLUSIONS

The high number of unidentified alleles in the nonclassical group suggests that less frequent mutations, or the presence of new ones, might be the cause of the disease in the Argentine population. Alternatively, the cut-off value in the ACTH-stimulated 17-hydroxyprogesterone test might overestimate the diagnosis of the nonclassical form by including some patients with heterozygous status.

Massive plasmocytosis due to methimazole-induced bone marrow toxicity

Pancytopenia is a rare complication of the thionamide therapy reported secondary to aplastic anemia, the bone marrow being invariably hypocellular. We present a case of a 16-year-old female with Graves' disease who presented with massive bone marrow plasmocytosis mimicking multiple myeloma. The patient had already been on methimazole for a month when she was admitted to the Pediatric Unit with the diagnosis of sepsis. CBC revealed pancytopenia. Bone marrow aspirations showed hypocellular-normocellular bone marrow, 98% of plasma cells. At that time, MMI was discontinued and the patient was started on broad-spectrum antibiotics, dexamethasone, and G-CSF. Bone marrow aspiration day +4 still showed hypo-normocellular marrow, with remaining 6% plasma cells. Myeloma screen was negative; ANC >1,000 at day +7, platelets >50,000 at day +24. Twenty-four months after patient's discharge, her clinical condition, CBC, and bone marrow remained normal. To our knowledge this is the first report of pancytopenia due to MMI, where the usual hypoplasia found is replaced by massive plasmocytosis.

Recurrent hypothermia, hypersomnolence, central sleep apnea, hypodipsia, hypernatremia, hypothyroidism, hyperprolactinemia and growth hormone deficiency in a boy--treatment with clomipramine

A boy referred at the age of 4 years because of obesity and under observation for 16 years, was found to be suffering from a hypothalamic syndrome of unknown origin characterized by progressive obesity, polyphagia, deficiency of growth and thyroid hormone, hyperprolactinemia, hypodipsia, hypernatremia and hyperosmolality without diabetes insipidus. At ages 11 and 16 there were 3 day episodes of spontaneous muscular weakness, hypersomnolence and hypothermia associated with central sleep apnea and severe bradycardia. Subsequently, decreased ventilatory responsiveness to carbon dioxide (CO2) was found as a consequence of blunted neural drive. Therapy with clomipramine HCl (Anafranil Ciba-Geigy) for 6 months led to a normalization of serum sodium levels, pulse rate, ventilatory response to dioxide with no recurrence of the central apnea within 4 following years.

Late-onset type of 21-hydroxylase deficiency in childhood

It was recently proposed that congenital and late-onset 21-hydroxylase deficiency are caused by two distinct recessive allelic genes. Although both genes are associated with the HLA system, only the late-onset type was found to be linked with the antigens B14 and DR1. Biochemical and immunological studies were conducted in two families with children suffering from 21-hydroxylase deficiency of postnatal onset. In the first family, of Jewish Ashkenazic origin, a 2 1/2-yr-old girl presenting with clitoromegaly was found to be homozygous for the antigens B14 and DR1. In the second family, of Arabic origin, all the children, their parents and a paternal aunt were clinically and/or biochemically affected, carrying the B14, but not the DR1 antigen on one or both HLA haplotypes. These data suggest that some cases of simple virilizing 21-hydroxylase deficiency in childhood are related to the late-onset type of 21-hydroxylase deficiency.

Testicular function in prepubertal male pseudohermaphroditism

Testicular function was evaluated in forty-one prepubertal patients with male pseudohermaphroditism by determining serum concentrations of progesterone, 17-hydroxyprogesterone, dehydroepiandrosterone, androstenedione, testosterone and dihydrotestosterone before and after stimulation with hCG and, in some instances, ACTH. Testosterone response to hCG was normal in all subjects. In one patient, a 4-year-old boy, a deficiency of 17,20-desmolase activity was diagnosed based on the coexistence of elevated levels of pregnenolone, 17-hydroxypregnenolone, progesterone and 17-hydroxyprogesterone and low levels of dehydroepiandrosterone and androstenedione. In three other patients enzymatic blocks were suspected but not confirmed. Congenital deficiency of enzymes necessary for testosterone biosynthesis is an uncommon aetiology of male pseudohermaphroditism.

Testicular function in post pubertal male pseudohermaphroditism

Testicular endocrine function was studied in twelve post pubertal patients with male pseudohermaphroditism and 46 XY chromosomal constitution. Patients were divided into three groups, four subjects who became feminized during puberty, five who became masculinized during puberty and three who were castrated before puberty. Serum dehydroepiandrosterone, progesterone, 17-hydroxyprogesterone, androstendione, testosterone, dihydrotestosterone, LH and FSH were determined by radioimmunoassay. Patients of the first group had the clinical characteristics of testicular feminization secondary to absence of the androgen receptor. One of the five patients of the second group had deficient testosterone secretion but no enzymatic defect could be demonstrated. One of the subjects castrated before puberty had a deficiency in 17,20-desmolase. Therefore, evidence of a failure of the fetal testes could be found in only two of the twelve patients studied.

Familial idiopathic hyperphosphatasia: a study of two young siblings treated with porcine calcitonin

A study of two siblings with a severe infantile form of familial idiopathic hyperphosphatasia is reported. A girl aged one year was followed for two years while receiving intermittent treatment with porcine calcitonin. This induced a clinical remission, a reduction of both the high serum level of alkaline phosphatase and the raised urinary excretion of hydroxyproline, and a remarkable improvement in bone structure as seen radiologically. Her sister aged two months received porcine calcitonin for three weeks, during which clinical improvement, no change in the serum level of alkaline phosphatase and a marked decrease of the excretion of hydroxyproline were recorded.