A de novo PRPF8 pathogenic variant in transient severe hypophosphatemia with delayed puberty and growth failure.

INTRODUCTION: Childhood hypophosphatemia is a rare condition and may be caused by malabsorption, malignancies, or genetic factors. Prolonged hypophosphatemia leads to impaired growth and radiographic signs of rickets. METHODS: We performed a detailed clinical and genetic evaluation of an adolescent boy with repeatedly low plasma phosphate concentrations (below 0.60 mmol/L), and growth failure. RESULTS: At 14 years, the patient presented with decelerating growth and delayed puberty. Biochemistry showed hypophosphatemia due to increased urinary phosphate loss; kidney function and vitamin D status were normal. Radiographs showed mild metaphyseal changes. A gene panel for known genetic hypophosphatemias was negative. Trio exome analysis followed by Sanger sequencing identified a pathogenic heterozygous de novo stop gain variant in PRPF8 gene, c.5548C>T p.(Arg1850*)., in the conserved RNase H homology domain. PRPF8 encodes the pre-RNA protein 8, which has a role in RNA processing. Heterozygous PRPF8 variants have been associated with retinitis pigmentosa and neurodevelopmental disorders but not with phosphate metabolism. The patient underwent growth hormone (GH) stimulation tests which confirmed GH deficiency. Head MRI indicated partially empty sella. GH treatment was started at 15 years. Surprisingly, phosphate metabolism normalized during GH treatment, suggesting that hypophosphatemia was at least partly secondary to growth hormone deficiency. CONCLUSION: In conclusion, the evaluation of an adolescent with profound long-term hypophosphatemia revealed a pituitary developmental defect associated with a stop gain variant in PRPF8. Hypophosphatemia alleviated with GH treatment. The pathological PRPF8 variant may contribute to abnormal pituitary development; however, its role in phosphate metabolism remains uncertain.

Bone structure assessed with pQCT in prepubertal males with delayed puberty or congenital hypogonadotropic hypogonadism.

OBJECTIVE: Congenital hypogonadotropic hypogonadism (CHH) is associated with impaired bone mineral density in adulthood, whereas the estimates on bone structure in adolescents with CHH has not been previously evaluated. This study describes bone structure in CHH patients and compares it to that in boys with constitutional delay of growth and puberty (CDGP). DESIGN: A cross-sectional study. METHODS: Peripheral quantitative computed tomography (pQCT) of non-dominant arm and left leg were performed. Volumetric bone mineral density (BMD), bone mineral content, and area in trabecular and cortical bone compartments were evaluated, and bone age-adjusted Z-scores for the bone parameters were determined. RESULTS: The participants with CHH had more advanced bone age and were older, taller and heavier than the CDGP boys, yet they had lower trabecular BMD in distal radius (147.7 mg/mm3 [95% CI, 128-168 mg/mm3 ] vs. 181.2 mg/mm3 [172-192 mg/mm3 ], p = .002) and distal tibia (167.6 mg/mm3 [145-190 mg/mm3 ] vs. 207.2 mg/mm3 [187-227 mg/mm3 ], p = .012), respectively. CHH males had lower cortical thickness at diaphyseal tibia than the participants with CDGP (p = .001). These between-group differences remained significant in corresponding Z-scores adjusted for bone age and height (p = .001). In CDGP group, serum testosterone correlated positively with trabecular BMD (r = 0.51, p = .013) at distal radius, and estradiol levels correlated positively with trabecular BMD at the distal site of tibia (r = 0.58, p = .004). CONCLUSIONS: Five treatment-naïve male patients with CHH exhibited poorer trabecular BMD than untreated males with CDGP. We speculate that timely low-dose sex steroid replacement in CHH males may benefit skeletal health in adulthood.

Biliary Anomalies in Patients With HNF1B Diabetes.

Context: The clinical spectrum of organogenetic anomalies associated with HNF1B mutations is heterogeneous. Besides cystic kidney disease, diabetes, and various other manifestations, odd cases of mainly neonatal and posttransplantation cholestasis have been described. The biliary phenotype is incompletely defined. Objective: To systematically characterize HNF1B-related anomalies in the bile ducts by imaging with magnetic resonance imaging (MRI) or magnetic resonance cholangiopancreatography (MRCP). Setting and Patients: Fourteen patients with HNF1B mutations in the catchment area of the Helsinki University Hospital were evaluated with upper abdominal MRI and MRCP. Blood samples and clinical history provided supplemental data on the individual phenotype. Main Outcome Measure(s): Structural anomalies in the biliary system, medical history of cholestasis, other findings in abdominal organs, diabetes and antihyperglycemic treatment, hypomagnesemia, and hyperuricemia. Results: Structural anomalies of the bile ducts were found in seven of 14 patients (50%). Six patients had choledochal cysts, which are generally considered premalignant. Conclusions: Structural anomalies of the biliary system were common in HNF1B mutation carriers. The malignant potential of HNF1B-associated choledochal cysts warrants further studies.