Near normalization of adult height and body proportions by growth hormone in pycnodysostosis

Pycnodysostosis: Characteristics of teeth, mouth and jaws

OBJECTIVES

To describe the clinical and radiographic oro-dental characteristics of patients with pycnodysostosis (PDO).

MATERIALS & METHODS

A short interview and clinical examination of seven patients with PDO were performed as well as assessment of the temporomandibular joints and masticatory muscles using the diagnostic criteria for temporomandibular disorders, DC-TMD form. A full set of records were taken including photos and intraoral scan. Finally, existing cone beam computed tomography (CBCT) images and radiographs were also studied.

RESULTS

All patients presented with bimaxillary micrognathia, five had a convex profile, and two had a straight profile. In addition, posterior open bite, Angle Class III molar relation with accompanying anterior crossbite and a grooved median palate were common findings. No patient showed symptoms of temporomandibular disorder (TMD) apart from some clicking. Finally, the main radiographic findings were the obtuse mandibular angle, the frontal bossing, the elongation of the coronoid/condylar process and the presence of hypercementosis with obliterated pulp chambers.

CONCLUSION

The examined patients with PDO were characterized by dental crowding, malocclusion (anterior crossbite, posterior open bite), hypercementosis, obliterated pulp chambers and deviations in mandibular morphology. In conclusion, patients with PDO have a specific need for dental and orthodontic monitoring with focus on crowding and posterior open bite. The patients will benefit from a long-term orthodontic plan including extractions.

Management of long bone fractures in patients with pycnodysostosis

Pycnodysostosis is a rare genetic condition that leads to generalised bony sclerosis and increased fracture risk. Orthopaedic specialists play a crucial role in managing affected children due to their susceptibility to frequent fractures. We had a case of a middle childhood female patient with pycnodysostosis and a femur fracture. Initially, an attempt using the Titanium Elastic Nailing System was made, but the sclerotic metaphyseal bone made it challenging. So, we opted for a 4.5 mm locked compressive plate, with multiple drill bits as a backup due to potential drill breakage. Though elastic nailing is preferred for paediatric long bone fractures, surgeons must be prepared for extremely sclerotic cortices and a narrow medullary canal when dealing with patients with pycnodysostosis. Open fixation and multiple drill bits in the toolkit are essential to overcome the potential obstacles during the procedure.

Evaluation of Clinical Characteristics and Growth Hormone Response in a Rare Skeletal Dysplasia: Pycnodysostosis

Introduction Pycnodysostosis is a rare osteosclerotic skeletal dysplasia; its clinical features include short stature, characteristic facial features, increased bone fragility, and acro-osteolysis of the distal phalanx. Lack of clear guidelines for treatment and follow-up in rare diseases such as pycnodysostosis with growth hormone (GH) deficiency poses a difficulty for the clinician. This study aims to identify clinical, radiological, and endocrine findings of patients with pycnodysostosis focusing on the first year of recombinant human growth hormone (rhGH) treatment response. The eminence of this study is that it presents clinical experience with rhGH, providing an approach for future similar cases. Methods Three girls and two boys from three different families diagnosed with pycnodysostosis via clinical, radiological, and genetic evaluation followed up in the pediatric endocrinology clinic between 2022 and 2023 were enrolled in this study. Clinical findings, anthropometric measurements (weight, height, body mass index [BMI]), and laboratory, radiological, and genetic examinations were evaluated retrospectively. Participants were evaluated for GH deficiency using L-DOPA and clonidine tests if growth rate was below -2 standard deviation score (SDS) for gender and age after one-year follow-up. Results Complaints on admission were short stature (80%) and recurrent bone fractures (20%). Characteristic facial features and brachydactyly were seen in all the patients. Median height SDS on admission was -3.0 (range: -1.9 to -3.8). Median height SDS on last clinic visit was -3.2 (range: -1.7 to -4.2) at a median age of 8 years (range: 3.5-14 years). BMI was normal in four patients, while one was overweight. Bone mineral densitometry z-score was high, and two patients had bone fractures following minor trauma, while one had recurrent fractures. Two siblings (first and second cases) and the third case were diagnosed with GH deficiency, and anterior pituitary hormones were normal otherwise. One had partial empty sella in hypophyseal magnetic resonance imaging. rhGH (33 mcg/kg/day, subcutaneously) was started. Growth rate of the first, second, and third cases increased from 3.3, 3.1, 3.9 to 5, 4.3, 7.2 cm/year, respectively. Prior to rhGH, two had adenoid hypertrophy which was stable following rhGH. Growth rate follow-up of the fourth case continues, while the fifth case, the only participant who has reached adult height, has normal height according to age and gender normative. Conclusion Although rare, pycnodysostosis should not be overlooked in a patient with characteristic facial features, disproportionate short stature, and recurrent fractures. GH deficiency should be evaluated early if growth rate is declining. rhGH may restore growth rate and the possibility of catch-up in growth in patients with pycnodysostosis and GH deficiency. Hence, after first year of rhGH, growth rate of patients with pycnodysostosis is lower when compared to other etiologies of GH deficiency.

Growth hormone treatment improves final height in children with X-linked hypophosphatemia

BACKGROUND/AIM

Despite optimal conventional treatment (oral phosphate supplements and active vitamin D analogs), about 40-50% of children with well-controlled X-linked hypophosphatemia (XLH) show linear growth failure, making them less likely to achieve an acceptable final height. Here, we studied the hypothesis that rhGH treatment improves final height in children with XLH and growth failure.

METHODS

Two cohorts of children with XLH were included in this retrospective longitudinal analysis: (1) a cohort treated with rhGH for short stature (n = 34) and (2) a cohort not treated with rhGH (n = 29). The mean duration of rhGH treatment was 4.4 ± 2.9 years. We collected the auxological parameters at various time points during follow-up until final height.

RESULTS

In rhGH-treated children, 2 years of rhGH therapy was associated with a significant increase in height from - 2.4 ± 0.9 to - 1.5 ± 0.7 SDS (p < 0.001). Their mean height at rhGH discontinuation was - 1.2 ± 0.9 SDS and at final height was - 1.3 ± 0.9 SDS corresponding to 165.5 ± 6.4 cm in boys and 155.5 ± 6.3 cm in girls. Notably, the two groups had similar final heights; i.e., the final height in children not treated with rhGH being - 1.2 ± 1.1 SDS (165.4 ± 6.8 cm in boys and 153.7 ± 7.8 cm in girls), p = 0.7.

CONCLUSION

Treatment with rhGH permits to improve final height in children with XLH and growth failure, despite optimal conventional treatment. We propose therefore that rhGH therapy could be considered as an option for short stature in the context of XLH.

Cathepsin K mutation-A subtle clinical presentation

Introduction

Pyknodysostosis is an uncommon inherited disorder associated with consanguinity; often presenting with sclerotic bone disease, short stature, dysmorphic features and recurrent fragility fractures at an early age.

Case history

A 34-year-old lady was evaluated for the cause of recurrent fragility fractures. She was born of a third-degree consanguineous marriage and had a twin brother who was short statured. The index patient had a height of 141 cm, dysmorphic features including frontoparietal bossing, blue sclera with short stubby fingers and toes. Radiological evaluation revealed diffuse osteosclerosis with acro-osteolysis exclusively in the toes, apart from mid-facial hypoplasia, lack of pneumatisation of the paranasal sinuses, dental abnormalities and scoliosis. Dual-energy X-ray absorptiometry revealed increased bone mineral density. Based on the clinical features, the patient was tested for Cathepsin K gene variants using Next Generation Sequencing, and was found to be positive for a novel homozygous c.224T&gt;C, p. Met75Thr likely pathogenic missense variant.

Discussion

This patient presented at a later age than expected with recurrent fragility fractures and the diagnosis was not suspected till adulthood, owing to the subtle clinical features. Confirmation with genetic testing helped in establishing the diagnosis.

Conclusion

Pyknodysostosis, although uncommon, is one of the differential diagnoses for diffuse osteosclerosis presenting with recurrent fragility fractures. Next generation sequencing in an appropriate setting may confirm the diagnosis.

Pycnodysostosis: A Growth Hormone Responsive Skeletal Dysplasia

Objective

Pycnodysostosis is commonly associated with growth hormone (GH) deficiency and responds well to GH therapy with achievement of normal or near-normal height and restoration of body proportions.

Case Report

A 22-month-old extremely short (−4.05 height standard deviation score) disproportionate boy with skeletal dysplasia presented to clinic. Skeletal survey, genetic panel, magnetic resonance imaging, and an insulin-like growth factor generation tests were performed.

Results

Skeletal survey showed increased bone density with classic features of pycnodysostosis, subsequently confirmed to be due to a deleterious homozygous frameshift mutation in CTSK. Uniquely among skeletal dysplasias, GH deficiency is a common association, secondary to pituitary hypoplasia. Magnetic resonance imaging confirmed pituitary hypoplasia and he subsequently underwent an insulin-like growth factor generation test that demonstrated biochemical responsiveness to GH therapy. This was thought to be safer than a classic GH stimulation test, in view of his very small size. Subsequently, his height has markedly improved on GH therapy. His height is now −2.25 SD, with an annualized growth velocity of 9.65 cm/y over a period of 18 months .

Conclusion

It is important to consider GH therapy in children with pycnodysostosis, with the greatest benefit seen in children started at a young age.

The genotypic and phenotypic spectrum of pycnodysostosis in Saudi Arabia: Novel variants and clinical findings

Pycnodysostosis is characterized by short stature, osteosclerosis, acro-osteolysis, increased tendency of fractures, and distinctive dysmorphic features. It is a rare autosomal recessive disease caused by biallelic CTSK mutations. The clinical details of 18 patients from Saudi Arabia were reviewed. Short stature, osteopetrosis, acro-osteolysis, and distinctive facial dysmorphism were documented in all cases. Our results highlight the significant complications associated with this disease. The large anterior fontanelle is one of the cardinal signs of this disease; however, half of our patients had small fontanelles and a quarter had craniosynostosis, which caused optic nerve compression. Sleep apnea was of the major complications in three patients. Bone fracture can be a presenting symptom, and in our patients it mainly occurred after the age of 3 years. Bone marrow suppression was seen in a single patient of our cohort who was misdiagnosed initially with malignant osteopetrosis. In this study, we also describe two novel (c.5G > A [p.Trp2Ter], c.538G > A [p.Gly180Ser]) and two reported (c.244-29 A > G, c.830C > T [p.Ala277Val]) CTSK mutations. Our results indicate that the recurrent intronic variant, c.244-29 A > G is likely to be a founder mutation, as it was found in 78% (14/18 patients) of our cohort belonging to the same tribe.

Phenotypic and genotypic spectrum of CTSK variants in a cohort of twenty-five Indian patients with pycnodysostosis

BACKGROUND

Pycnodysostosis is an autosomal recessive skeletal dysplasia with easily recognizable clinical features and marked molecular heterogeneity. In this study, we explored the clinical and molecular spectrum of 25 Indian patients with pycnodysostosis from 20 families.

METHODS

Clinical information was collected on a predesigned clinical proforma. Sanger method was employed to sequence all the exons and exon/intron boundaries of the CTSK gene. Novel variants were systematically assessed by prediction softwares and protein modelling. The pathogenicity of variant was established based on ACMG-AMP criteria. An attempt was also made to establish a genotype-phenotype correlation and devise a diagnostic scoring system based on clinical and radiological findings.

RESULTS

Consanguinity and positive family history were present in 65% (13/20) and 45% (9/20) of the families respectively. Short stature and fractures were the predominant presenting complaints and was evident in 96% (24/25) and 32% (8/25) of affected individuals respectively. Gestalt facial phenotype and acro-osteolysis were present in 76% (19/25) and 82.6% (19/23) of the individuals respectively. Hepatosplenomegaly was present in 15% (3/20) of the individuals with one of them having severe anaemia. Causative sequence variations were identified in all of them. A total of 19 variants were identified from 20 families amongst which 10 were novel. Homozygous variants were identified in 90% (18/20) families. Amongst the novel variants, there was a considerable proportion (40%) of frameshift variants (4/10). No significant genotype-phenotype correlation was noted. Scoring based on clinical and radiological findings led to the proposal that a minimum of 2 scores in each category is required in addition to high bone density to diagnose pycnodysostosis with certainty.

CONCLUSION

This study delineated the genotypic and phenotypic characterisation of Indian patients with pycnodysostosis with identification of 10 novel variants. We also attempted to develop a clinically useful diagnostic scoring system which requires further validation.

Clinical and genetic evaluation of Danish patients with pycnodysostosis

BACKGROUND

Pycnodysostosis is a rare autosomal recessive osteosclerotic skeletal dysplasia caused by variants in the cathepsin K gene (CTSK). Clinical features include short stature, bone fragility, characteristic facial features and acro-osteolysis of the distal phalanges. Usually, patients suffer from multiple bone fractures. The purpose of this study was to describe the Danish population of pycnodysostosis patients with respect to genotype, phenotype and the prevalence of complications. We collected medical history, performed clinical examination, collected blood- and urine samples, performed dual-energy x-ray absorptiometry scan (DXA) and high-resolution peripheral quantitative computed tomography scan (HRpQCT) and obtained clinical photos. Information about complications, bone mineral density and bone markers in the blood were collected and analysed.

RESULTS

Ten patients with a median age of 32 years ranging from five to 51 years participated. The pycnodysostosis phenotype varied with respect to the number of bone fractures and degree of complications. DXA and HRpQCT showed high bone mineral density. A tendency of growth hormone treatment escalating growth and increasing final height was seen. A marker of bone resorption measured in blood was within normal range in nine patients and elevated in one patient. A novel pathogenic variant in CSTK causing pycnodysostosis was detected in two related patients. Moreover information about the patients' own health perception was reported. An example being they rated their mental health to be good despite multiple bone fractures.

CONCLUSION

This study provides information about genotypes and phenotypes in a Danish pycnodysostosis population. It reports new data about the complications such as bone fractures and it elucidates the levels of bone turnover markers as well as the density of the bones in one of the biggest cohort of pycnodysostosis patients ever published. An individualised approach to treatment in this patient group is necessary as the phenotype including complications varies between patients. Additional studies are needed to further understand genotype-phenotype correlations.

A Case Report of Pycnodysostosis Associated with Multiple Pituitary Hormone Deficiencies and Response to Treatment

Pycnodysostosis is a rare autosomal recessive osteosclerotic bone disorder associated with short stature and multiple bony abnormalities. Growth hormone (GH) deficiency may contribute to short stature in about 50% of patients. Available literature has rarely reported other pituitary hormone deficiencies in pyknodysostosis. Though the management remains conservative, recombinant human GH (rhGH) has been tried in selected patients. Here we present a case of pycnodysostosis which was evaluated for associated co-morbidities and found to have multiple pituitary hormone deficiencies. A 7-year-old girl was referred to our centre for evaluation of short stature. On examination, she had frontal and occipital bossing, limited mouth opening, hyperdontia with multiple carries, short and stubby digits and short stature. Investigation revealed dense sclerotic bones with frontal and occipital bossing, non-fusion of sutures with obtuse mandibular angle, non-pneumatised sinuses, small ‘J’ shaped sella turcica, acro-osteolysis of digits and absent medullary cavities. Cathepsin-K gene mutation analysis confirmed the diagnosis of pycnodysostosis. She was screened for associated co-morbidities and was found to have concomitant GH deficiency. Treatment with rhGH brought about an increase of 1 standard deviation score in height over 2 years and also unmasked central hypothyroidism at three months necessitating thyroxine replacement.

Cathepsins in the Pathophysiology of Mucopolysaccharidoses: New Perspectives for Therapy

Cathepsins (CTSs) are ubiquitously expressed proteases normally found in the endolysosomal compartment where they mediate protein degradation and turnover. However, CTSs are also found in the cytoplasm, nucleus, and extracellular matrix where they actively participate in cell signaling, protein processing, and trafficking through the plasma and nuclear membranes and between intracellular organelles. Dysregulation in CTS expression and/or activity disrupts cellular homeostasis, thus contributing to many human diseases, including inflammatory and cardiovascular diseases, neurodegenerative disorders, diabetes, obesity, cancer, kidney dysfunction, and others. This review aimed to highlight the involvement of CTSs in inherited lysosomal storage disorders, with a primary focus to the emerging evidence on the role of CTSs in the pathophysiology of Mucopolysaccharidoses (MPSs). These latter diseases are characterized by severe neurological, skeletal and cardiovascular phenotypes, and no effective cure exists to date. The advance in the knowledge of the molecular mechanisms underlying the activity of CTSs in MPSs may open a new challenge for the development of novel therapeutic approaches for the cure of such intractable diseases.

A Novel Variant c.847T>C in CTSK Gene Leading to Pycnodysostosis: A Case Report

Pycnodysostosis is a rare genetic disorder with a prevalence of 1.7 per million births; it usually presents with short stature, osteosclerosis, increased bone fragility, and acro-osteolysis of distal phalanges. There are less than 200 cases reported worldwide and very few from South-East Asia. We present a case of pycnodysostosis who presented with short stature, acro-osteolysis of distal phalanges, and on genetic testing revealing a variant c.847T>C, p.Y283H, in exon 7 of the CTSK in homozygous state: not reported till date to the best of our knowledge.

Genetic study of eight Egyptian patients with pycnodysostosis: identification of novel CTSK mutations and founder effect

This is the first Egyptian study with detailed clinical and orodental evaluation of eight patients with pycnodysostosis and identification of four mutations in CTSK gene with two novel ones and a founder effect.

INTRODUCTION

Pycnodysostosis is a rare autosomal recessive skeletal dysplasia due to mutations in the CTSK gene encoding for cathepsin K, a lysosomal cysteine protease.

METHODS

We report on the clinical, orodental, radiological, and molecular findings of eight patients, from seven unrelated Egyptian families with pycnodysostosis.

RESULTS

All patients were offspring of consanguineous parents and presented with the typical clinical picture of the disorder including short stature, delayed closure of fontanels, hypoplastic premaxilla, obtuse mandibular angle, and drum stick terminal phalanges with dysplastic nails. Their radiological findings showed increased bone density, acro-osteolysis, and open cranial sutures. Mutational analysis of CTSK gene revealed four distinct homozygous missense mutations including two novel ones, c.164A>C (p. K55T) and c.433G>A (p.V145M). The c.164A>C (p. K55T) mutation was recurrent in three unrelated patients who also shared similar haplotype, suggesting a founder effect.

CONCLUSION

Our findings expand the mutational spectrum of CTSK gene and emphasize the importance of full clinical examination of all body systems including thorough orodental evaluation in patients with pycnodysostosis.

Two-year recombinant human growth hormone (rhGH) treatment is more effective in pre-pubertal compared to pubertal short children with X-linked hypophosphatemic rickets (XLHR)

CONTEXT

Twenty-five to 40% of patients with well-controlled X-linked hypophosphatemic rickets (XLHR) have a final height under -2 SDS. Previous studies have shown that recombinant human growth hormone (rhGH) treatment improves linear growth in short children with XLHR.

OBJECTIVE

We studied the effectiveness of rhGH treatment in children with XLHR in a larger cohort.

DESIGN

Monocentric, prospective, non-randomized trial.

SETTING

University hospital in France.

PATIENTS

19 patients with XLHR and a mutation in the PHEX gene. Six male and 6 female Tanner stage 1 patients (age 6.1±2.4years) and 4 male and 3 female Tanner stage 2 patients (age 13.1±1years). At inclusion, height SDS was -2.35±0.8 SDS and growth velocity was -1.12±1.2 SDS.

INTERVENTION

2years of treatment with 67mcg/kg/day of rhGH at initiation. Every three months rhGH dosage was adjusted using an IGF-1 dosing protocol.

MAIN OUTCOME MEASURES

Comparison in change from baseline to year 2 in height and growth velocity.

RESULTS

Height SDS improved from -2.35±0.8 SDS at baseline, to -1.62±0.8 SDS (p=0.01) after one and to -1.2±1 SDS (p=0.04) after two years of rhGH treatment. There was a strong correlation (r²=0.6104, p<0.0001) between the age of onset of rhGH treatment and the number of cm gained over the study period. Pre-pubertal patients height SDS improved compared to baseline height SDS after one (-1.5±0.7, p<0.03) and two (-0.96±1, p<0.03) years of rhGH treatment. In pubertal patients there was no significant improvement in height SDS after one year (-1.75±1) and after two years (-1.7±0.8) of rhGH treatment.

CONCLUSION

Two-year rhGH treatment is effective to treat short stature in XLHR children. Pre-pubertal children responded better to rhGH.

CLINICAL TRIAL REGISTRATION NUMBER

NCT02720770.

Cathepsin K Inhibitors for Osteoporosis: Biology, Potential Clinical Utility, and Lessons Learned

Cathepsin K is a cysteine protease member of the cathepsin lysosomal protease family. Although cathepsin K is highly expressed in osteoclasts, lower levels of cathepsin K are also found in a variety of other tissues. Secretion of cathepsin K from the osteoclast into the sealed osteoclast-bone cell interface results in efficient degradation of type I collagen. The absence of cathepsin K activity in humans results in pycnodysostosis, characterized by increased bone mineral density and fractures. Pharmacologic cathepsin K inhibition leads to continuous increases in bone mineral density for ≤5 years of treatment and improves bone strength at the spine and hip. Compared with other antiresorptive agents, cathepsin K inhibition is nearly equally efficacious for reducing biochemical markers of bone resorption but comparatively less active for reducing bone formation markers. Despite multiple efforts to develop cathepsin K inhibitors, potential concerns related to off-target effects of the inhibitors against other cathepsins and cathepsin K inhibition at nonbone sites, including skin and perhaps cardiovascular and cerebrovascular sites, prolonged the regulatory approval process. A large multinational randomized, double-blind phase III study of odanacatib in postmenopausal women with osteoporosis was recently completed. Although that study demonstrated clinically relevant reductions in fractures at multiple sites, odanacatib was ultimately withdrawn from the regulatory approval process after it was found to be associated with an increased risk of cerebrovascular accidents. Nonetheless, the underlying biology and clinical effects of cathepsin K inhibition remain of considerable interest and could guide future therapeutic approaches for osteoporosis.

Novel mutation and white matter involvement in an Indian child with pycnodysostosis

Pycnodysostosis (OMIM # 265800) is an inherited lysosomal disorder due to affection of cathepsin K gene, localised to 1q21. Pycnodysostosis can present with both skeletal and extraskeletal features. The index patient presented with cardinal features of short stature, dental and digital anomalies with history of multiple fractures. He, in addition had an unreported finding of white matter hyperintensity suggesting dysmyelination on neuroimaging. Molecular analysis revealed a homozygous insertion of single nucleotide in exon 5 of the CTSK gene that produces the substitution of phenylalanine instead of leucine at position 160 of protein and a premature termination of protein synthesis due to insertion of a stop codon. This mutation (c.480_481insT), (p.L160fsX173) is a novel frameshift mutation. The index case extends the phenotypic spectrum and the list of previously reported mutations in the CTSK gene.

A pilot study of growth hormone administration in boys with predicted adult short stature and near-ending growth

CONTEXT

The growth-promoting effect of starting recombinant human growth hormone (rhGH) at the time of near-ending growth has not been studied in sexually mature boys who will have idiopathic short stature (ISS) as adults because it is believed that such an advanced stage of puberty would preclude favorable results.

OBJECTIVES

1) To explore the effects of starting rhGH administration at time of near-ending growth in boys with ISS. 2) To search for predictors of response to rhGH.

SUBJECTS

Fifteen boys aged 15.5 ± 1 years terminating puberty were growing at a rate < 2 cm/6 months towards a predicted adult height (PAH) <-2.5 SDS.

METHODS

Participants received 0.50 ± 0.06 mg/kg · wk of rhGH according to a target-to-treat protocol. When growth became less than 0.5 cm in 3 months or when height has reached 169 cm, rhGH was ceased. Testosterone, growth velocity (GV), height, serum IGF-1, bone age (BA) at hand-wrist and knee score were measured at onset; IGF-1 and height were monitored every 3 months. A formula for PAH was developed. Height increment (HI, adult height-starting height) and height gain (HG, adult height-PAH) were calculated.

RESULTS

Following rhGH administration for 11.1 ± 4.8 months, GV-SDS increased from -2.5 ± 1.7 to 3.5 ± 4.3 (P = 2 × 10(-4)), HI = 8.5 ± 3.7 cm, HG = 6.8 ± 4.8 cm and adult height was -1.8 ± 0.9 SDS, compared to a PAH of -2.9 ± 0.6 SDS (P = 4 × 10(-4)). Knee score (P = 2 × 10(-3)), GV at rhGH onset (P = 8 × 10(-3)) and rhGH dose (P = 8 × 10(-3)) were identified as predictors of HI and HG, but BA was not.

CONCLUSIONS

Our study suggests that 1) a short period of rhGH administration can increase true adult height significantly in boys with ISS at time of near-ending growth; and 2) knee score rather than BA should be used to identify rhGH responders. These preliminary observations await confirmation by larger randomized trials.

Current research on pycnodysostosis

Pycnodysostosis is a rare autosomal recessive disorder caused by an inactivating mutation in cathepsin K (CTSK) and characterized by dysmorphic facial features, a short stature, acroosteolysis, osteosclerosis with increased bone fragility, and delayed closure of cranial sutures. Patients usually present with short stature or dysmorphic features the Pediatric Endocrinology or Genetics clinics, with atypical fractures to the orthopedics clinics or hematological abnormalities to the hematology clinics. However, under-diagnosis or misdiagnosis of this condition is a major issue. Pycnodysostosis is not a life threatening condition, but craniosynostosis, frequent fractures, respiratory-sleep problems, and dental problems may cause significant morbidity. Although no specific treatment for this disorder has been described, patients should be followed for complications and treated accordingly. A specific treatment for the disorder must be established in the future to prevent complications and improve quality of life for patients in the current era of advanced molecular research.

A novel mutation (R122Q) in the cathepsin K gene in a Chinese child with Pyknodysostosis

BACKGROUND

Pyknodysostosis (OMIM 265800) is a rare, autosomal recessive sclerosing skeletal dysplasia as a consequence of the diminished capacity of osteoclasts to degrade organic bone matrix. Pyknodysostosis is caused by mutation in the cathepsin K (CTSK) gene. Up to date, 34 different CTSK mutations have been identified in patients with Pyknodysostosis; however, only one mutation was previously identified in a Chinese patient. The objective of this study was to characterize the clinical manifestations and features of Pyknodysostosis and identify the mutation of the causative gene in a Chinese family with Pyknodysostosis.

METHODS

We investigated a non-consanguineous Chinese family in which an 11-year-old child was affected with Pyknodysostosis. Altogether, 203 persons, including the affected individual, his parents and 200 healthy donors, were recruited and genomic DNA was extracted. All 8 exons of the CTSK gene, including the exon-intron boundaries, were amplified and sequenced directly.

RESULTS

The proband displayed a novel homozygous missense mutation c.365G>A in exon 4 of the CTSK gene. This mutation leads to the substitution of the arginine at position 122 by glutamine (R122Q) in cathepsin K. The parents were heterozygous for this gene mutation, and the mutation was not found in the 200 unrelated controls.

CONCLUSION

Our study suggests that the novel missense mutation c.365G>A (R122Q) in exon 4 of CTSK gene was responsible for Pyknodysostosis in the Chinese family.

A pilot study of discontinuous, insulin-like growth factor 1-dosing growth hormone treatment in young children with FGFR3 N540K-mutated hypochondroplasia

OBJECTIVE

To assess the growth promoting effect of a recombinant growth hormone (rGH) treatment protocol adjusted on insulin-like growth factor 1 (IGF-1) dosing in children affected by the most severe forms of FGFR3 N540K-mutated hypochondroplasia.

STUDY DESIGN

Midterm results of an open-label, single-center, nonrandomized, 2003-2020 pilot trial to final stature, including 6 children (mean age, 2.6 ± 0.7 years; mean height SDS, -3.0 ± 0.5) with the N540K mutation of FGFR3 gene who received an rGH dosage titrated to an IGF-1 level close to 1.5 SDS of the normal range. rGH therapy was interrupted 1 day per week, 1 month per year, and 6 months every 2 years.

RESULTS

The mean height SDS increased by 1.9 during the 6.1 ± 0.9-year study period, reaching -0.8 to -1.3 at age 8.7 ± 1 years. The mean±SDS baseline IGF-1 value was -1.6 ± 0.5 before rGH treatment and 1.4±0.3 during the last year of observation. The average cumulative rGH dose was 0.075 ± 0.018 mg/kg/day (range, 0.059-0.100 mg/kg/day). Trunk/leg disproportion was improved.

CONCLUSION

IGF-1-dosing rGH treatment durably improves growth and reduces body disproportion in children with severe forms of hypochondroplasia.

Clinical and animal research findings in pycnodysostosis and gene mutations of cathepsin K from 1996 to 2011

Cathepsin K (CTSK) is a member of the papain-like cysteine protease family. Mutations in the CTSK gene cause a rare autosomal recessive bone disorder called pycnodysostosis (OMIM 265800). In order to follow the advances in the research about CTSK and pycnodysostosis, we performed a literature retrospective study of 159 pycnodysostosis patients reported since 1996 and focused on the genetic characteristics of CTSK mutations and/or the clinical phenotypes of pycnodysostosis. Thirty three different CTSK mutations have been found in 59 unrelated pycnodysostosis families. Of the 59 families, 37.29% are from Europe and 30.51% are from Asia. A total of 69.70% of the mutations were identified in the mature domain of CTSK, 24.24% in the proregion, and 6.06% in the preregion. The hot mutation spots are found in exons 6 and 7. CTSK mutations result in total loss or inactivity of the CTSK protein, which causes abnormal degradation of bone matrix proteins such as type I collagen. Skeletal abnormalities, including short stature, an increase in bone density with pathologic fractures, and open fontanels and sutures, are the typical phenotypes of pycnodysostosis. Research on Ctsk(-/-) mouse models was also reviewed here to elucidate the biological function of Ctsk and the mechanism of pycnodysostosis. New evidence suggests that Ctsk plays an important role in the immune system and may serve as a valid therapeutic target in the future treatment of pycnodysostosis.

Therapy of growth disorders

PURPOSE OF REVIEW

We review recent developments in the therapy of growth disorders, focusing mainly on recent developments in the field of growth hormone (GH) therapy.

RECENT FINDINGS

Review of current practice reveals wide variation in the approach to short stature and the institution of GH therapy. No new indications for GH treatment have been approved by the Food and Drug Administration since 2007, but off-label use has been explored in several chronic illnesses. There is also increasing focus on GH effects beyond increase in stature (e.g. effects on body composition and bone density). As the experience with GH increases, the long-term risks and outcomes are better understood and risks appear to be low. Data regarding beneficial effects of GH in Prader-Willi syndrome are accumulating but questions remain about patient selection, start age and safety. Recombinant insulin-like growth factor 1 has become more widely available and has been aggressively promoted for Food and Drug Administration-approved indications as well as off-label uses in the last few years. The use of aromatase inhibitors has been tempered by concern about side-effects and lack of efficacy.

SUMMARY

Growth hormone remains the mainstay of therapy for growth disorders, though other options, including recombinant insulin-like growth factor 1, are being investigated in various settings.