Johnny Deladoëy

Utility of whole‐exome sequencing for those near the end of the diagnostic odyssey: time to address gaps in care

An accurate diagnosis is an integral component of patient care for children with rare genetic disease. Recent advances in sequencing, in particular whole‐exome sequencing (WES), are identifying the genetic basis of disease for 25–40% of patients. The diagnostic rate is probably influenced by when in the diagnostic process WES is used. The Finding Of Rare Disease GEnes (FORGE) Canada project was a nation‐wide effort to identify mutations for childhood‐onset disorders using WES. Most children enrolled in the FORGE project were toward the end of the diagnostic odyssey. The two primary outcomes of FORGE were novel gene discovery and the identification of mutations in genes known to cause disease. In the latter instance, WES identified mutations in known disease genes for 105 of 362 families studied (29%), thereby informing the impact of WES in the setting of the diagnostic odyssey. Our analysis of this dataset showed that these known disease genes were not identified prior to WES enrollment for two key reasons: genetic heterogeneity associated with a clinical diagnosis and atypical presentation of known, clinically recognized diseases. What is becoming increasingly clear is that WES will be paradigm altering for patients and families with rare genetic diseases.

Is the Incidence of Congenital Hypothyroidism Really Increasing? A 20-Year Retrospective Population-Based Study in Québec

CONTEXTnCongenital hypothyroidism (CH) is reportedly increasing in the United States, possibly reflecting changes in screening methods. In Québec, the same initial TSH cutoff (15 mU/liter) has been used for the last 20 yr, but in 2001, the cutoff was decreased from 15 to 5 mU/liter for the second test, which is requested when TSH is intermediate (15-30 mU/liter) on the first.nnnOBJECTIVESnOur objective was to assess the incidence of CH over the last 20 yr in Québec.nnnDESIGN, SETTING, PATIENTS, AND MAIN OUTCOME MEASUREnThis is a population-based retrospective study. Incidences by etiology based on thyroid scintigraphy with technetium were compared between 1990-2000 and 2001-2009.nnnRESULTSnOf 1,660,857 newborns over 20 yr, 620 had CH (incidence 1:2679). Etiology was dysgenesis (n = 389, 1:4270), either ectopy (n = 290) or athyreosis (n = 99), goiter (n = 52, 1:31,940), normal-size gland in situ (n = 115, 1:14,442), and unknown (n = 64, 1:25,950). The new screening algorithm identified 49 additional cases (i.e. 25 normal-size gland in situ, 12 unknown etiology, 10 ectopies, and two goiters). Consequently, the incidence of normal-size gland in situ or of unknown etiology more than doubled (1:22,222 to 1:9,836, P = 0.0015; and 1:43,824 to 1:17,143, P = 0.0018, respectively) but that of dysgenesis and goiter remained stable. Had the 1990-2000 algorithm been applied in 2001-2009, no change in incidence would have been observed in any category.nnnCONCLUSIONnEstimating the incidence of CH is influenced by minimal changes in TSH screening cutoffs. Lower cutoffs identify additional cases that have predominantly functional disorders whose impact on intellectual disability, if left untreated, remains to be determined.

Lethal respiratory failure and mild primary hypothyroidism in a term girl with a de novo heterozygous mutation in the TITF1/NKX2.1 gene.

CONTEXTnThyroid transcription factor 1 (TITF1/NKX2.1) is expressed in the thyroid, lung, ventral forebrain, and pituitary. In the lung, TITF1/NKX2.1 activates the expression of genes critical for lung development and function. Titf/Nkx2.1(-/-) mice have pituitary and thyroid aplasia but also impairment of pulmonary branching. Humans with heterozygous TITF1/NKX2.1 mutations present with various combinations of primary hypothyroidism, respiratory distress, and neurological disorders.nnnOBJECTIVEnThe objective of the study was to report clinical and molecular studies of the first patient with lethal neonatal respiratory distress from a novel heterozygous TITF1/NKX2.1 mutation.nnnPARTICIPANTnThis girl, the first child of healthy nonconsanguineous French-Canadian parents, was born at 41 wk. Birth weight was 3,460 g and Apgar scores were normal. Soon after birth, she developed acute respiratory failure with pulmonary hypertension. At neonatal screening on the second day of life, TSH was 31 mU/liter (N <15) and total T(4) 245 nmol/liter (N = 120-350). Despite mechanical ventilation, thyroxine, surfactant, and pulmonary vasodilators, the patient died on the 40th day.nnnRESULTSnHistopathology revealed pulmonary tissue with low alveolar counts. The thyroid was normal. Sequencing of the patients lymphocyte DNA revealed a novel heterozygous TITF1/NKX2.1 mutation (I207F). This mutation was not found in either parent. In vitro, the mutant TITF-1 had reduced DNA binding and transactivation capacity.nnnCONCLUSIONnThis is the first reported case of a heterozygous TITF1/NKX2.1 mutation leading to neonatal death from respiratory failure. The association of severe unexplained respiratory distress in a term neonate with mild primary hypothyroidism is the clue that led to the diagnosis.

Variation by Ethnicity in the Prevalence of Congenital Hypothyroidism Due to Thyroid Dysgenesis

BACKGROUNDnThe scant data on ethnic differences in the prevalence of congenital hypothyroidism (CH) have generally not taken etiology of CH into account. Our hypothesis is that the prevalence of CH due to thyroid dysgenesis (TD) varies by ethnicity.nnnMETHODSnThis case-control study included all patients with CH due to TD (a condition of unknown origin) or to dyshormonogenesis (DH, of known autosomal recessive transmission) between 1987 and 2009. Etiology was established by (99m)Tc scintigraphy. The parents self-assessed their ethnicity, which we grouped in Caucasian, Hispanic, black, Asian, and Maghreb/Middle East. We compared ethnicity between the 190 patients with TD (147 ectopies, 40 athyreoses, and 3 orthotopic hypoplasias) and the 44 patients with DH. Ethnicity was also compared to the reference population of the city of Montreal. Prevalence odds ratios (POR) were calculated and compared by the bilateral Fishers exact test.nnnRESULTSnThe ethnic composition of the DH group was similar to that of the reference population. In blacks, TD prevalence of 1 in 190 (0.5%) was low compared to that of DH (4 in 44; 9.1%; POR 0.06; 95% confidence interval: 0.001-0.56; pu2009=u20090.005). In contrast, Caucasians showed an increased TD prevalence of 166 in 190 (87.3%) compared to that of DH (30 in 44; 68.2%; POR 3.21; 95% confidence interval: 1.37-7.34; pu2009=u20090.0052). No statistically significant differences were observed between other ethnic groups.nnnCONCLUSIONnTD is less prevalent in blacks and more prevalent in Caucasians. Blacks being more genetically diverse, this is an argument for an oligogenic inheritance of susceptibility to TD.

Transcriptome, Methylome and Genomic Variations Analysis of Ectopic Thyroid Glands

Background Congenital hypothyroidism from thyroid dysgenesis (CHTD) is predominantly a sporadic disease characterized by defects in the differentiation, migration or growth of thyroid tissue. Of these defects, incomplete migration resulting in ectopic thyroid tissue is the most common (up to 80%). Germinal mutations in the thyroid-related transcription factors NKX2.1, FOXE1, PAX-8, and NKX2.5 have been identified in only 3% of patients with sporadic CHTD. Moreover, a survey of monozygotic twins yielded a discordance rate of 92%, suggesting that somatic events, genetic or epigenetic, probably play an important role in the etiology of CHTD. Methodology/Principal Findings To assess the role of somatic genetic or epigenetic processes in CHTD, we analyzed gene expression, genome-wide methylation, and structural genome variations in normal versus ectopic thyroid tissue. In total, 1011 genes were more than two-fold induced or repressed. Expression array was validated by quantitative real-time RT-PCR for 100 genes. After correction for differences in thyroid activation state, 19 genes were exclusively associated with thyroid ectopy, among which genes involved in embryonic development (e.g. TXNIP) and in the Wnt pathway (e.g. SFRP2 and FRZB) were observed. None of the thyroid related transcription factors (FOXE1, HHEX, NKX2.1, NKX2.5) showed decreased expression, whereas PAX8 expression was associated with thyroid activation state. Finally, the expression profile was independent of promoter and CpG island methylation and of structural genome variations. Conclusions/Significance This is the first integrative molecular analysis of ectopic thyroid tissue. Ectopic thyroids show a differential gene expression compared to that of normal thyroids, although molecular basis could not be defined. Replication of this pilot study on a larger cohort could lead to unraveling the elusive cause of defective thyroid migration during embryogenesis.

Bioinactive ACTH Causing Glucocorticoid Deficiency

CONTEXTnA 4-year-old girl and a 4-month-old boy presented with hypoglycemia, normal electrolytes, low cortisol, and high ACTH. A diagnosis of primary adrenal insufficiency was made and initial treatment was with glucocorticoids and mineralocorticoids. The genes known to cause ACTH resistance were normal. Whole exome sequencing revealed that the girl was compound heterozygous for POMC mutations: one previously described null allele and one novel p.R8C mutation in the sequence encoding ACTH and α-MSH. The boy was homozygous for the p.R8C mutation.nnnHYPOTHESISnThe p.R8C ACTH mutant is immunoreactive, but the mutant peptides, ACTH-R8C and α-MSH-R8C, are bioinactive.nnnMETHODSnMethods included whole exome sequencing, Sanger sequencing, peptide synthesis, ACTH immunoradiometric assay, hormone binding, and activation assays in cells expressing melanocortin receptors.nnnRESULTSnACTH-R8C was immunoreactive but failed to bind and activate cAMP production in melanocortin-2 receptor (MC2R)-expressing cells, and α-MSH-R8C failed to bind and stimulate cAMP production in MC1R- and MC4R-expressing cells.nnnCONCLUSIONnThese are the first documented cases of glucocorticoid deficiency due to the secretion of an ACTH molecule that lacks biological bioactivity but conserves immunoreactivity. POMC mutations should thus be considered in patients presenting with apparent ACTH resistance. Our findings also highlight a limitation to immunoassay-based diagnostics and demonstrate the value of genetic analysis. Establishing the molecular etiology of the disorder in our patients allowed cessation of the unnecessary mineralocorticoids. Finally, discovery of this mutation indicates that in humans, the amino acid sequence His(6)Phe(7)Arg(8)Trp(9) is important not only for cAMP activation but also for ACTH binding to MC2R.

Are guidelines for glucocorticoid coverage in adrenal insufficiency currently followed

OBJECTIVESnTo search for evidence of acute adrenal failure linked to inappropriate use of stress management protocols.nnnSTUDY DESIGNnPatients followed up for primary adrenal insufficiency (n = 102) or secondary adrenal insufficiency (n = 34) between 1973 and 2007 were included. All hospitalizations, both urgent (n = 157) and elective (n = 90), were examined. We recorded clinical evidence of acute adrenal failure, parental management before admission, and details of glucocorticoid prescription and administration in the hospital setting.nnnRESULTSnFor urgent hospitalizations, subgroup and time period did not influence the percentage of patients hospitalized (primary adrenal insufficiency 45%; secondary adrenal insufficiency 38%; P = .55). The use of stress glucocorticoid doses by parents increased significantly after 1997 (P < .05), although still only 47% increased glucocorticoids before hospitalization. Stress doses were more frequently administered on arrival in our emergency department after 1990 (P < .05); patients with signs or symptoms of acute adrenal failure decreased to 27% after 1997 (P < .01). Twenty-four percent of all hospitalizations were marked by suboptimal adherence to glucocorticoid stress protocols, with rare but significant clinical consequences.nnnCONCLUSIONSnIn spite of an increased use of glucocorticoid stress dose protocols by parents and physicians, patients remain at risk of morbidity and death from acute adrenal failure. This risk may be minimized with conscientious application of stress protocols, but other patient-specific risk factors may also be implicated.

Congenital Secondary Hypothyroidism Due to a Mutation C105Vfs114X Thyrotropin-β Mutation: Genetic Study of Five Unrelated Families from Switzerland and Argentina

We identified five patients with congenital secondary hypothyroidism with isolated thyrotropin (TSH) deficiency originating from three and two unrelated Argentinean and Swiss families, respectively. The affected patients presented with both low TSH as well as low thyroid hormone levels. Further, TSH-releasing hormone (TRH) stimulation failed to increase serum TSH, whereas prolactin increased adequately. These affected children were homozygous for a 1-bp deletion (822delT) in the TSH-beta subunit gene leading to a cysteine 105 to valine conversion (C105V) and to a frameshift with a premature stop codon at position 114 (C105Vfs114X). In a total of 22 families five different mutations located within the coding region of the TSH-beta subunit gene responsible for congenital secondary hypothyroidism have been reported so far (E12X; G29R; Q49X; IVS2 +5, G --> A; C105Vfs114X). Importantly, out of 13 families, including our five families, the C105Vfs114X mutation has been described in 12 unrelated and non-consanguineous families, whereas the remaining four TSH-beta subunit gene mutations have been described in consanguineous families only. Therefore the C105Vfs114X mutation within the TSH-beta subunit gene is the most frequent alteration causing congenital secondary hypothyroidism (13 of 22; 59%) and occurs mainly in unrelated and non-consanguineous families (12 of 13; 92%). As we could exclude a common ancestry by microsatellite marker analysis in our five independent families we concluded that the codon 105 in the TSH-beta subunit gene might be a hot spot, although a founder effect has been reported in certain cases clustered in a highly specific and restricted geographical area.

A high prevalence of dual thyroid ectopy in congenital hypothyroidism: evidence for insufficient signaling gradients during embryonic thyroid migration or for the polyclonal nature of the thyroid gland?

BACKGROUNDnThyroid ectopy results from the failure of the thyroid precursor cells to migrate from the primordial pharynx to the anterior part of the neck. Most ectopic thyroids are revealed by congenital hypothyroidism and present as a single round mass at the base of the tongue, with no other thyroid tissue. However, some cases have dual ectopy, with part of the tissue having partially migrated. We hypothesized that this occurs more frequently than previously reported.nnnMETHODSnTo determine the prevalence of dual ectopy, we reviewed the pertechnetate scintigraphies of 81 patients with congenital hypothyroidism from thyroid ectopy diagnosed between 2002 and 2011 at our institution.nnnRESULTSnWe report a series of seven cases (9%) of dual ectopy, representing an incidence ranging from 1:50,000 to 1:70,000.nnnCONCLUSIONSnAlmost one in 10 cases with congenital hypothyroidism due to thyroid ectopy has dual ectopy. This suggests that two populations of cells diverged at an early stage of development, which may arise from insufficient signaling gradients in surrounding tissues during early organogenesis or may indirectly support the polyclonal nature of the thyroid.

Ectopic Thyroid Gland Causing Dysphonia: Imaging and Molecular Studies

Endocrinology Service and Research Center (S.S.-V., J.D.), Otorhinolaryngology Department (A.L.), and Nuclear Medicine Service (S.T.), Centre Hospitalier Universitaire Sainte-Justine, Department of Pediatrics, University of Montreal, Montreal, Canada H3T 1C5; and Institut de Recherche Interdisciplinaire en Biologie Humaine et Moleculaire and Genetics Service (C.R., G.V.), Erasme Hospital, Free University of Brussels, B-1070 Brussels, Belgium