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.

Clinical case seminar in pediatric thyroid disease.

Pediatric thyroid diseases cover a large spectrum of congenital and acquired forms, ranging from congenital primary or central hypothyroidism, autoimmune thyroid disease, iodine deficiency, rare genetic defects of thyroid hormone action, metabolism and cell membrane transport to benign nodules and malignant tumors. The previous 15 papers of the textbook Paediatric Thyroidology gave a systematic overview of the current knowledge and guidelines on all these diseases. In this final paper, the authors collected a series of patient histories from their clinics illustrating frequently encountered clinical problems and providing key learning points and references to each case. Although not fully comprehensive, it aims at providing relevant clinical knowledge on thyroid diseases of the neonate, the child, and the adolescent.

46, XY gonadal dysgenesis: new SRY point mutation in two siblings with paternal germ line mosaicism.

Familial recurrence risks are poorly understood in cases of de novo mutations. In the event of parental germ line mosaicism, recurrence risks can be higher than generally appreciated, with implications for genetic counseling and clinical practice. In the course of treating a female with pubertal delay and hypergonadotropic hypogonadism, we identified a new missense mutation in the SRY gene, leading to somatic feminization of this karyotypically normal XY individual. We tested a younger sister despite a normal onset of puberty, who also possessed an XY karyotype and the same SRY mutation. Imaging studies in the sister revealed an ovarian tumor, which was removed. DNA from the father's blood possessed the wild type SRY sequence, and paternity testing was consistent with the given family structure. A brother was 46, XY with a wild type SRY sequence strongly suggesting paternal Y-chromosome germline mosaicism for the mutation. In disorders of sexual development (DSDs), early diagnosis is critical for optimal psychological development of the affected patients. In this case, preventive karyotypic screening allowed early diagnosis of a gonadal tumor in the sibling prior to the age of normal puberty. Our results suggest that cytological or molecular diagnosis should be applied for siblings of an affected DSD individual.

Autosomal dominant neurohypophyseal diabetes insipidus in a Swiss family, caused by a novel mutation (C59Delta/A60W) in the neurophysin moiety of prepro-vasopressin-neurophysin II (AVP-NP II).

OBJECTIVE: To study clinical, morphological and molecular characteristics in a Swiss family with autosomal dominant familial neurohypophyseal diabetes insipidus (adFNDI). PARTICIPANTS AND METHODS: A 15-month-old girl presenting with symptoms of polydipsia and polyuria was investigated by water deprivation test. Evaluation of the family revealed three further family members with symptomatic vasopressin-deficient diabetes insipidus. T1-weighted magnetic resonance images of the posterior pituitary were taken in two affected adult family members and molecular genetic analysis was performed in all affected individuals. RESULTS: The water deprivation test in the 15-month-old child confirmed the diagnosis of vasopressin-deficient diabetes insipidus and the pedigree was consistent with autosomal dominant inheritance. The characteristic bright spot of the normal vasopressin-containing neurophypophysis was absent in both adults with adFNDI. Direct sequence analysis revealed a new deletion (177-179DeltaCGC) in exon 2 of the AVP-NP II gene in all affected individuals. At the amino acid level, this deletion eliminates cysteine 59 (C59Delta) and substitutes alanine 60 by tryptophan (A60W) in the AVP-NP II precursor; interestingly, the remainder of the reading frame remains unchanged. According to the three-dimensional structure of neurophysin, C59 is involved in a disulphide bond with C65. CONCLUSIONS: Deletion of C59 and substitution of A60W in the AVP-NP II precursor is predicted to disrupt one of the seven disulphide bridges required for correct folding of the neurophysin moiety and thus disturb the function of neurophysin as the vasopressin transport protein. These data are in line with the clinical and morphological findings in the reported family with adFNDI.

New autosomal recessive mutation of the TSH-beta subunit gene causing central isolated hypothyroidism.

We identified a new nonsense mutation of the TSH-beta subunit gene responsible for a severe isolated TSH deficiency in two children from the same consanguineous kindred. These affected children are homozygous for a C-to-T transition at nucleotide 654 of the TSH-beta subunit gene, leading to the conversion of a glutamine (CAG) to a premature stop codon (TAG) in the codon 49 (Q49X). The resulting nascent peptide does not contain the seat belt region (amino acid residues 88-105), a TSH-beta subunit region crucial for the dimerization with the alpha-subunit, and, hence, the correct secretion of the mature TSH heterodimer is hampered. Free T(3), free T(4) as well as basal TSH levels were extremely low in both affected individuals and, importantly, TRH stimulations failed to increase serum TSH, but not PRL, confirming isolated TSH deficiency. Using the new StyI endonuclease restriction site generated by the mutation, we confirmed that the affected children were homozygous for the Q49X TSH-beta mutation whereas their unaffected parents as well as their unaffected brother were heterozygous. Consequently, this isolated TSH deficiency follows an autosomal recessive mode of inheritance.

Autosomal dominant GH deficiency due to an Arg183His GH-1 gene mutation: clinical and molecular evidence of impaired regulated GH secretion.

G to A transition at position 6664 of the GH-1 gene results in the substitution of Arg183 by His (R183H) in human GH protein and causes a new form of autosomal dominant isolated GH deficiency (type II). Although a weak GH release after standard pharmacological provocation tests is observed in these affected individuals, the dominant inheritance pattern is postulated to be caused by a blockade of the GH-regulated secretion in the somatotrophs. The aim of this study was to analyze the impact of this autosomal dominant mutation not only at a clinical, but also at a cellular, level. The results of the different stimulation tests showed first that the patient possesses a severely impaired, but releasable, GH store, and second that the GH secretion is blocked in a time-dependent and reversible way. To confirm these clinical data, cell culture studies were performed looking at the regulated secretory pathway of GH using AtT-20 cells. Importantly, we were able to show that when the R183H mutant GH was expressed in AtT-20 cells, secretagogue (forskolin) induced a normal R183H GH-regulated secretion, but in AtT-20 cells coexpressing both the R183H mutant GH and the normal GH, forskolin-induced GH secretion was markedly reduced. Together, the experiments seem to support the hypothesis that R183H mutant GH severely impaired the GH-regulated secretion and may, therefore, be the cause of this specific form of isolated GH deficiency type II.

Regulation of human GH receptor gene transcription by 20 and 22 kDa GH in a human hepatoma cell line.

The human GH gene is 1.7 kilobase pairs (kb) in length and is composed of five exons and four introns. This gene is expressed in the pituitary gland and encodes a 22 kDa protein. In addition to this predominant (75%) form, 5-10% of pituitary GH is present as a 20 kDa protein that has an amino acid (aa) sequence identical to the 22 kDa form except for a 15 aa internal deletion of residues 32-46 as a result of an alternative splicing event. Because it has been reported that non-22-kDa GH isoforms might be partly responsible for short stature and growth retardation in children, the aim of this study was to compare the impact of both 22 kDa and 20 kDa GH on GH receptor gene (GH receptor/GH binding protein (GHR/GHBP)) expression. Various concentrations of 20 kDa and 22 kDa GH (0, 2, 5, 12.5, 25, 50 and 150 ng/ml) were added to human hepatoma (HuH7) cells cultured in serum-free hormonally defined medium for 0, 1 and 2 h. Thereafter GHR/GHBP mRNA expression was measured by quantitative PCR. Addition of either 20 kDa or 22 kDa GH, at low or normal physiological concentrations (0, 2, 5, 12.5, 25 or 50 ng/ml) induced a dose-dependent increase in GHR/GHBP expression. However, a supraphysiological concentration of 20 kDa GH (150 ng/ml) resulted in a significantly lower (P<0.05) downregulation of GHR/GHBP gene transcription compared with the downregulation achieved by this concentration of 22 kDa GH. This difference might be explained by a decreased ability to form a 1 : 1 complex with GHR and/or GHBP, which normally occurs at high concentrations of GH. Nuclear run-on experiments and GHBP determinations confirmed the changes in GHR/GHBP mRNA levels. In conclusion, we report that both 20 kDa and 22 kDa GH, in low and normal physiological concentrations, have the same effect on regulation of GHR/GHBP gene transcription in a human hepatoma cell line. At a supraphysiological concentration of 150 ng/ml, however, 20 kDa GH has a less self-inhibitory effect than the 22 kDa form.

Aromatase deficiency caused by a novel P450arom gene mutation: impact of absent estrogen production on serum gonadotropin concentration in a boy.

We identified a new point mutation in the CYP19 gene responsible for aromatase (P450arom) deficiency in a 46,XY male infant with unremarkable clinical findings at birth. This boy is homozygote for a 1-bp (C) deletion in exon 5 of the aromatase gene causing a frame-shift mutation. The frame-shift results in a prematurely terminated protein that is inactive due to the absence of the functional regions of the enzyme. Aromatase deficiency was suspected prenatally because of the severe virilization of the mother during the early pregnancy, and the diagnosis was confirmed shortly after birth. Four weeks after birth, the baby boy showed extremely low levels of serum estrogens, but had a normal level of serum free testosterone; in comparison with the high serum concentration of androstenedione at birth, a striking decrease occurred by 4 weeks postnatally. We previously reported elevated basal and stimulated FSH levels in a female infant with aromatase deficiency in the first year of life. In contrast, in the male infant, basal FSH and peak FSH levels after standard GnRH stimulation tests were normal. This finding suggests that the contribution of estrogen to the hypothalamic-pituitary gonadotropin-gonadal feedback mechanism is different in boys and girls during infancy and early childhood. In normal girls, serum estradiol concentrations strongly correlate with circulating inhibin levels, and thus, low inhibin levels may contribute to the striking elevation of FSH in young girls with aromatase deficiency. In contrast, estradiol levels are physiologically about a 7-fold lower in boys than in girls, and serum inhibin levels remain elevated even though levels of FSH, LH, and testosterone are decreased.

"Hot spot" in the PROP1 gene responsible for combined pituitary hormone deficiency.

As pituitary function depends on the integrity of the hypothalamic-pituitary axis, any defect in the development and organogenesis of this gland may account for a form of combined pituitary hormone deficiency (CPHD). Although pit-1 was 1 of the first factors identified as a cause of CPHD in mice, many other homeodomain and transcription factors have been characterized as being involved in different developmental stages of pituitary gland development, such as prophet of pit-1 (prop-1), P-Lim, ETS-1, and Brn 4. The aims of the present study were first to screen families and patients suffering from different forms of CPHD for PROP1 gene alterations, and second to define possible hot spots and the frequency of the different gene alterations found. Of 73 subjects (36 families) analyzed, we found 35 patients, belonging to 18 unrelated families, with CPHD caused by a PROP1 gene defect. The PROP1 gene alterations included 3 missense mutations, 2 frameshift mutations, and 1 splice site mutation. The 2 reported frameshift mutations could be caused by any 2-bp GA or AG deletion at either the 148-GGA-GGG-153 or 295-CGA-GAG-AGT-303 position. As any combination of a GA or AG deletion yields the same sequencing data, the frameshift mutations were called 149delGA and 296delGA, respectively. All but 1 mutation were located in the PROP1 gene encoding the homeodomain. Importantly, 3 tandem repeats of the dinucleotides GA at location 296-302 in the PROP1 gene represent a hot spot for CPHD. In conclusion, the PROP1 gene seems to be a major candidate gene for CPHD; however, further studies are needed to evaluate other genetic defects involved in pituitary development.

Phenotypic variability in familial combined pituitary hormone deficiency caused by a PROP1 gene mutation resulting in the substitution of Arg-->Cys at codon 120 (R120C).

As pituitary function depends on the integrity of the hypothalamic-pituitary axis, any defect in the development and organogenesis of this gland may account for a form of combined pituitary hormone deficiency (CPHD). A mutation in a novel, tissue-specific, paired-like homeodomain transcription factor, termed Prophet of Pit-1 (PROP1), has been identified as causing the Ames dwarf (df) mouse phenotype, and thereafter, different PROP1 gene alterations have been found in humans with CPHD. We report on the follow-up of two consanguineous families (n = 12), with five subjects affected with CPHD (three males and two females) caused by the same nucleotide C to T transition, resulting in the substitution of Arg-->Cys in PROP1 at codon 120. Importantly, there is a variability of phenotype, even among patients with the same mutation. The age at diagnosis was dependent on the severity of symptoms, ranging from 9 months to 8 yr. Although in one patient TSH deficiency was the first symptom of the disorder, all patients became symptomatic by exhibiting severe growth retardation and failure to thrive, which was mainly caused by GH deficiency (n = 4). The secretion of the pituitary-derived hormones (GH, PRL, TSH, LH, and FSH) declined gradually with age, following a different pattern in each individual; therefore, the deficiencies developed over a variable period of time. All of the subjects entered puberty spontaneously, and the two females also experienced menarche and periods before a replacement therapy was necessary.