Arrate Pereda

PRKAR1A and PDE4D Mutations Cause Acrodysostosis but Two Distinct Syndromes with or without GPCR-Signaling Hormone Resistance

CONTEXT Acrodysostosis is a rare skeletal dysplasia that is associated with multiple resistance to G protein-coupled receptor (GPCR) signaling hormones in a subset of patients. Acrodysostosis is genetically heterogeneous because it results from heterozygous mutations in PRKAR1A or PDE4D, two key actors in the GPCR-cAMP-protein kinase A pathway. OBJECTIVE Our objective was to identify the phenotypic features that distinguish the two genotypes causing acrodysostosis. PATIENTS AND METHODS Sixteen unrelated patients with acrodysostosis underwent a candidate-gene approach and were investigated for phenotypic features. RESULTS All patients had heterozygous de novo mutations. Fourteen patients carried a PRKAR1A mutation (PRKAR1A patients), five each a novel PRKAR1A mutation (p.Q285R, p.G289E, p.A328V, p.R335L, or p.Q372X), nine the reported PRKAR1A p.R368X mutation; two patients harbored a mutation in PDE4D (PDE4D patients) (one novel mutation, p.A227S; one reported, p.E590A). All PRKAR1A, but none of the PDE4D mutated patients were resistant to PTH and TSH. Two PRKAR1A patients each with a novel mutation presented a specific pattern of brachydactyly. One PDE4D patient presented with acroskyphodysplasia. Additional phenotypic differences included mental retardation in PDE4D patients. In addition, we report the presence of pigmented skin lesions in PRKAR1A and PDE4D patients, a feature not yet described in the acrodysostosis entity. CONCLUSIONS All PRKAR1A and PDE4D patients present similar bone dysplasia characterizing acrodysostosis. Phenotypic differences, including the presence of resistance to GPCR-cAMP signaling hormones in PRKAR1A but not PDE4D patients, indicate phenotype-genotype correlations and highlight the specific contributions of PRKAR1A and PDE4D in cAMP signaling in different tissues.

Brachydactyly E: isolated or as a feature of a syndrome

Brachydactyly (BD) refers to the shortening of the hands, feet or both. There are different types of BD; among them, type E (BDE) is a rare type that can present as an isolated feature or as part of more complex syndromes, such as: pseudohypopthyroidism (PHP), hypertension with BD or Bilginturan BD (HTNB), BD with mental retardation (BDMR) or BDE with short stature, PTHLH type. Each syndrome has characteristic patterns of skeletal involvement. However, brachydactyly is not a constant feature and shows a high degree of phenotypic variability. In addition, there are other syndromes that can be misdiagnosed as brachydactyly type E, some of which will also be discussed. The objective of this review is to describe some of the syndromes in which BDE is present, focusing on clinical, biochemical and genetic characteristics as features of differential diagnoses, with the aim of establishing an algorithm for their differential diagnosis. As in our experience many of these patients are recruited at Endocrinology and/or Pediatric Endocrinology Services due to their short stature, we have focused the algorithm in those steps that could mainly help these professionals.

Novel microdeletions affecting the GNAS locus in pseudohypoparathyroidism: characterization of the underlying mechanisms.

CONTEXT Pseudohypoparathyroidism type Ia (PHP1A) is a rare endocrine disorder characterized by hypocalcemia, hyperphosphatemia, multiple hormonal resistance, and features of Albright hereditary osteodystrophy. When the phenotype is present but not associated with hormonal resistance, it is called psedopseudohypoparathyroidism (PPHP). Both entities have been associated to GNAS haploinsufficiency, and are mostly caused by inherited inactivating mutations at GNAS gene that codes for the stimulatory alpha subunit of G protein, although the cause remains unidentified in approximately 30% of patients. OBJECTIVES The aims of our work were 1) to identify GNAS locus defects in 112 patients with clinical diagnosis of PHP1A/PPHP and no point mutations at GNAS, to improve molecular diagnostic and genetic counseling; 2) to outline the underlying molecular mechanism(s). METHODS Methylation-specific-multiplex ligation-dependent probe amplification, qPCR, array comparative genomic hybridization, and long-PCR were used to search for genomic rearrangements at chromosome 20q and to identify their boundaries. We used different bioinformatic approaches to assess the involvement of the genomic architecture in the origin of the deletions. RESULTS We discovered seven novel genomic deletions, ranging from 106-bp to 2.6-Mb. The characterization of five of seven deletion breakpoints and the definition of the putative molecular mechanisms responsible for these rearrangements revealed that Alu sequences play a major role in determining the genetic instability of the region. CONCLUSION We observed that deletions at GNAS locus represent a significant cause of PPHP/PHP1A and that such defects are mostly associated with Alu-mediated recombination events. Their investigation revealed to be fundamental as, in some cases, they could be misdiagnosed as imprinting defects.

Report of two novel mutations in PTHLH associated with brachydactyly type E and literature review

Autosomal‐dominant brachydactyly type E is a congenital limb malformation characterized by small hands and feet as a result of shortened metacarpals and metatarsals. Alterations that predict haploinsufficiency of PTHLH, the gene coding for parathyroid hormone related protein (PTHrP), have been identified as a cause of this disorder in seven families. Here, we report three patients affected with brachydactyly type E, caused by PTHLH mutations expected to result in haploinsufficiency, and discuss our data compared to published reports.

Pseudohypoparathyroidism vs. tricho-rhino-phalangeal syndrome: patient reclassification

Abstract Objectives: Given that tricho-rhino-phalangeal syndrome (TRPS) and pseudohypoparathyroidism/pseudopseudohypoparathyroidism (PHP/PPHP) are very rare monogenic disorders that share some features (distinctive facies, short stature, brachydactyly and, in some patients, intellectual disability) that lead to their misdiagnosis in some cases, our objective was to identify clinical, biochemical or radiological signs that could help to distinguish these two syndromes. Methods and results: We report on two cases, which were referred to the Endocrinology and Pediatric Endocrinology Services for obesity. Clinical evaluation initially suggested the diagnosis of PHP-Ia [phenotype suggestive of Albright hereditary osteodystrophy (AHO) with parathyroid hormone (PTH) resistance] and PPHP (phenotype resembling AHO, without PTH resistance), but (epi)genetic analysis of the GNAS locus ruled out the suspected diagnosis. Further clinical re-evaluation prompted us to suspect TRPS, and this was confirmed genetically. Conclusion: TRPS was mistakenly identified as PHP/PPHP because of the coexistence of obesity and brachydactyly, with PTH resistance in one of the cases. Specific traits such as sparse scalp hair and a pear-shaped nose, present in both cases, can be considered pathognomonic signs of TRPS, which could help us to reach a correct diagnosis.

Genetic and Epigenetic Defects at the GNAS Locus Lead to Distinct Patterns of Skeletal Growth but Similar Early-Onset Obesity: DISTINCT PATTERNS OF FETAL AND POSTNATAL GROWTH IN GNAS-RELATED DISORDERS

Pseudohypoparathyroidism type 1A (PHP1A), pseudoPHP (PPHP), and PHP type 1B (PHP1B) are caused by maternal and paternal GNAS mutations and abnormal methylation at maternal GNAS promoter(s), respectively. Adult PHP1A patients are reportedly obese and short, whereas most PPHP patients are born small. In addition to parathyroid hormone (PTH) resistance, PHP1A and PHP1B patients may display early‐onset obesity. Because early‐onset and severe obesity and short stature are daily burdens for PHP1A patients, we aimed at improving knowledge on the contribution of the GNAS transcripts to fetal and postnatal growth and fat storage. Through an international collaboration, we collected growth and weight data from birth until adulthood for 306 PHP1A/PPHP and 220 PHP1B patients. PHP1A/PPHP patients were smaller at birth than healthy controls, especially PPHP (length Z‐score: PHP1A –1.1 ± 1.8; PPHP –3.0 ± 1.5). Short stature is observed in 64% and 59% of adult PHP1A and PPHP patients. PHP1B patients displayed early postnatal overgrowth (height Z‐score at 1 year: 2.2 ± 1.3 and 1.3 ± 1.5 in autosomal dominant and sporadic PHP1B) followed by a gradual decrease in growth velocity resulting in normal adult height (Z‐score for both: –0.4 ± 1.1). Early‐onset obesity characterizes GNAS alterations and is associated with significant overweight and obesity in adults (bodey mass index [BMI] Z‐score: 1.4 ± 2.6, 2.1 ± 2.0, and 1.4 ± 1.9 in PPHP, PHP1A, and PHP1B, respectively), indicating that reduced Gsα expression is a contributing factor. The growth impairment in PHP1A/PPHP may be due to Gsα haploinsufficiency in the growth plates; the paternal XLαs transcript likely contributes to prenatal growth; for all disease variants, a reduced pubertal growth spurt may be due to accelerated growth plate closure. Consequently, early diagnosis and close follow‐up is needed in patients with GNAS defects to screen and intervene in case of early‐onset obesity and decreased growth velocity.

The p.R56* mutation in PTHLH causes variable brachydactyly type E

The p.R56 Mutation in PTHLH Causes Variable Brachydactyly Type E Arrate Pereda, Lucia Garzon-Lorenzo, Intza Garin, Jaime Cruz-Rojo, Jaime Sanchez del Pozo, and Guiomar Perez de Nanclares* Molecular (Epi) Genetics Laboratory, OSI Araba, University Hospital, Vitoria-Gasteiz, Spain Department of Biochemistry and Molecular Biology, University of Basque Country, Leioa, Spain Department of Pediatrics, Division of Endocrinology, 12 de Octubre Hospital, Madrid, Spain

Diagnosis and management of pseudohypoparathyroidism and related disorders: first international Consensus Statement

This Consensus Statement covers recommendations for the diagnosis and management of patients with pseudohypoparathyroidism (PHP) and related disorders, which comprise metabolic disorders characterized by physical findings that variably include short bones, short stature, a stocky build, early-onset obesity and ectopic ossifications, as well as endocrine defects that often include resistance to parathyroid hormone (PTH) and TSH. The presentation and severity of PHP and its related disorders vary between affected individuals with considerable clinical and molecular overlap between the different types. A specific diagnosis is often delayed owing to lack of recognition of the syndrome and associated features. The participants in this Consensus Statement agreed that the diagnosis of PHP should be based on major criteria, including resistance to PTH, ectopic ossifications, brachydactyly and early-onset obesity. The clinical and laboratory diagnosis should be confirmed by a molecular genetic analysis. Patients should be screened at diagnosis and during follow-up for specific features, such as PTH resistance, TSH resistance, growth hormone deficiency, hypogonadism, skeletal deformities, oral health, weight gain, glucose intolerance or type 2 diabetes mellitus, and hypertension, as well as subcutaneous and/or deeper ectopic ossifications and neurocognitive impairment. Overall, a coordinated and multidisciplinary approach from infancy through adulthood, including a transition programme, should help us to improve the care of patients affected by these disorders.This Consensus Statement gives recommendations for the diagnosis and management of patients with pseudohypoparathyroidism and related disorders. A coordinated and multidisciplinary approach from infancy through adulthood is recommended to improve the care of these patients.

What to consider when pseudohypoparathyroidism is ruled out: iPPSD and differential diagnosis

BackgroundPseudohypoparathyroidism (PHP) is a rare disease whose phenotypic features are rather difficult to identify in some cases. Thus, although these patients may present with the Albright’s hereditary osteodystrophy (AHO) phenotype, which is characterized by small stature, obesity with a rounded face, subcutaneous ossifications, mental retardation and brachydactyly, its manifestations are somewhat variable. Indeed, some of them present with a complete phenotype, whereas others show only subtle manifestations. In addition, the features of the AHO phenotype are not specific to it and a similar phenotype is also commonly observed in other syndromes. Brachydactyly type E (BDE) is the most specific and objective feature of the AHO phenotype, and several genes have been associated with syndromic BDE in the past few years. Moreover, these syndromes have a skeletal and endocrinological phenotype that overlaps with AHO/PHP. In light of the above, we have developed an algorithm to aid in genetic testing of patients with clinical features of AHO but with no causative molecular defect at the GNAS locus. Starting with the feature of brachydactyly, this algorithm allows the differential diagnosis to be broadened and, with the addition of other clinical features, can guide genetic testing.MethodsWe reviewed our series of patients (n = 23) with a clinical diagnosis of AHO and with brachydactyly type E or similar pattern, who were negative for GNAS anomalies, and classify them according to the diagnosis algorithm to finally propose and analyse the most probable gene(s) in each case.ResultsA review of the clinical data for our series of patients, and subsequent analysis of the candidate gene(s), allowed detection of the underlying molecular defect in 12 out of 23 patients: five patients harboured a mutation in PRKAR1A, one in PDE4D, four in TRPS1 and two in PTHLH.ConclusionsThis study confirmed that the screening of other genes implicated in syndromes with BDE and AHO or a similar phenotype is very helpful for establishing a correct genetic diagnosis for those patients who have been misdiagnosed with “AHO-like phenotype” with an unknown genetic cause, and also for better describing the characteristic and differential features of these less common syndromes.

Transient neonatal diabetes mellitus and hypomethylation at additional imprinted loci: novel ZFP57 mutation and review on the literature

Aim6q24-related transient neonatal diabetes mellitus (6q24-TNDM) is a rare imprinting disorder characterized by uncontrolled hyperglycemia during the first 6 months of life. The molecular etiology of 6q24-TNDM is attributable to overexpression of the paternally inherited PLAGL1 and HYMAI genes located on the 6q24 locus. One of these major defects is maternal loss of methylation (LOM) at 6q24. In addition, approximately 50% of TNDM patients that present LOM at 6q24 can also display hypomethylation at additional imprinted loci (multilocus imprinting disturbances, MLID). Interestingly, the majority of these patients carry mutations in the ZFP57 gene, a transcription factor required for the adequate maintenance of methylation during early embryonic development.MethodsMethylation analysis of 6q24 and additional imprinted loci was carried out by MS-MLPA in a Tunisian male patient with clinical diagnosis of TNMD. For the same patient, mutation analysis of the ZFP57 gene was conducted by direct Sanger sequencing.ResultsWe report a novel nonsense mutation (c.373C > T; p.R125*; ENST00000376883.1) at the ZFP57 gene causing TNDM-MLID and describe detailed phenotype/epigenotype analysis of TNMD patients carrying ZFP57 mutations.ConclusionWe provide additional support to the role of ZFP57 as a genetic determinant cause of MLID in patients with TNMD.