A Girl With Beckwith-Wiedemann Syndrome and Pseudohypoparathyroidism Type 1B Due to Multiple Imprinting Defects Free

Context:

Several patients with Beckwith-Wiedemann Syndrome (BWS) with multiple imprinting defects found by genetic analysis have been described. However, only two cases have been described with both genetic and clinical signs and symptoms of multiple diseases caused by imprinting defects.

Case Description:

The girl in this case presented at the age of 6 months with morbid obesity (body mass index, +7.5 SDS) and a large umbilical hernia. Genetic analysis showed BWS (hypomethylation of the KCNQ1OT1 gene). Calcium homeostasis was normal, and she had no signs of Albright hereditary osteodystrophy. At the age of 10 years, she presented with fatigue, and laboratory analyses showed marked hypocalcemia with signs of PTH resistance, but without evidence for Albright hereditary osteodystrophy, thus suggesting pseudohypoparathyroidism type 1B. Consistent with this diagnosis, methylation analysis of the GNAS complex revealed hypomethylation (about 20%) of the GNAS exon 1A, NESPAS, and GNASXL loci and hypermethylation (100% methylation) of the NESP locus.

Conclusions:

Imprinting defects at several different loci can occur in some patients, thus causing multiple different diseases. Symptoms of pseudohypoparathyroidism type 1B may be absent at diagnosis of BWS, yet prolonged subclinical hypocalcemia and/or hyperphosphatemia can have negative consequences (eg, intracerebral calcifications, myocardial dysfunction). We therefore suggest that patients with an imprinting disorder should be monitored for elevations in PTH, and epigenetic analysis of the GNAS complex locus should be considered.

Genomic imprinting is an epigenetic phenomenon restricting gene expression to either the paternally or the maternally derived gene copy. DNA methylation of specific genes during gametogenesis is an important mechanism to achieve this parent-specific gene expression in offspring, and Beckwith-Wiedemann syndrome (BWS) is a classic example of a disorder that can be caused by abnormal genomic imprinting. Several authors have reported that some patients with imprinting disorders have a more generalized imprinting defect, with hypomethylation at a range of maternally methylated imprinting control regions (ICRs) (1–5). As far as we know, only two cases are reported with both genetic and clinical diagnosis of multiple imprinting-related diseases (ie, Prader-Willi syndrome and BWS, and transient neonatal diabetes mellitus and BWS) (6, 7). We report a girl with BWS, caused by loss of methylation at the KCNQ1OT1 gene, who developed hypocalcemia due to pseudohypoparathyroidism caused by an imprinting defect at the GNAS complex locus.

Materials and Methods

Methylation at KCNQ1OT1 (LIT1) and H19 was measured by methylation-sensitive restriction digestion as previously described (8). Methylation of the GNAS region was analyzed by methylation-specific MLPA (MLPA kit ME031-A2; MRC Holland).

Case Report

Initial presentation

The reported girl is the second child of nonconsanguineous Caucasian parents, born after an uncomplicated spontaneous pregnancy at gestational age 40

weeks, birth weight 4380 g (+2.0 SDS, for Dutch reference growth charts) (9). At the age of 6 months, she presented with obesity. Her weight was 14.8 kg (+7.5 SDS, for Dutch reference growth charts) (9), and her height was 69 cm (+1.0 SDS, for Dutch reference growth charts) (10). Physical examination showed a large umbilical hernia and obesity, but no other dysmorphic figures (especially, no macroglossia, ear pits, nevus flammeus, or hemihypertrophy). Her psychomotor development was normal. Laboratory investigation showed no abnormalities in thyroid function, glucose homeostasis, somatotroph function, cortisol secretion, or calcium homeostasis (calcium, 2.57 mmol/L; phosphate, 1.99 mmol/L; PTH, 5.6 pmol/L). Methylation analysis of KCNQ1OT1 and H19 showed a lack of methylation of KCNQ1OT1, confirming the clinical diagnosis of BWS.

Infancy and childhood

After the diagnosis of BWS, follow-up consisted of regular abdominal ultrasounds and measurements of serum α-fetoprotein and urinary calcium excretion. No abnormalities were found during follow-up. At the age of 4.5 years, mild learning difficulties were noticed. Additional genetic analysis consisting of a SNP-array (Affymetrix 250K Nsp Array) revealed a normal female profile.

Presentation with hypocalcemia

At the age of 10 years, she complained of fatigue and abdominal pain. Screening for possible causes revealed hypocalcemia (serum calcium, 1.90 mmol/L), and additional serum analyses of calcium homeostasis (Table 1) showed hyperphosphatemia, normal serum alkaline phosphatase, low 25-hydroxyvitamin D, and hyperparathyroidemia. Urinary calcium was not detectable (urinary calcium < 0.5 mmol/L), and urinary phosphate excretion was diminished (filtered phosphate that is reabsorbed by renal tubules, 96.7%). The combination of hypocalcemia, hyperphosphatemia, hyperparathyroidemia, lack of hyperphosphaturia, and normal serum alkaline phosphatase was consistent with PTH resistance at the kidney.

Case reports (11) and personal experience indicated that prolonged and severe vitamin D deficiency could result in PTH resistance. Treatment with calcium and vitamin D3 was therefore initiated (calcium 1500 mg/d in three doses, vitamin D 1200 IU/d, after 2 wk followed by a weekly dose of 25 000 IU for 6 wk). This resulted in normalization of serum 25-hydroxyvitamin D after 2 months, but the other abnormalities in serum and urine remained (Table 1). Bone mineral density, estimated using dual-energy x-ray absorption (Lunar DPXL), was completely normal according to age-, gender-, and machine-specific Dutch references (Z-score total body, +0.2; lumbar spine, +0.1) (12).

The clinical diagnosis of pseudohypoparathyroidism (PHP) was made, and because of the absence of phenotypical signs of Albright hereditary osteodystrophy, PHP type 1B was suspected. Treatment with alfacalcidol (1.0 μg/d in two doses) was initiated and resulted in normalization of serum calcium, but PTH levels remained elevated (Table 1). Higher doses of alfacalcidol (2.0 μg/d in two doses) were prescribed but did not result in normal PTH levels (Table 1). The patient admitted being noncompliant with her oral calcium therapy, thus raising concerns that she did not faithfully take her vitamin D metabolite either. Consistent with this conclusion, her PTH levels remained elevated, which presumably enhanced calcium absorption in distal renal tubules leading to low urinary calcium excretion.

Methylation analysis of the GNAS exons by MLPA (Kit ME031-A2) revealed no deletions and hypomethylation (about 20%) of the GNAS exon 1A, NESPAS and GNASXL loci and 100% methylation of NESP locus, consistent with the clinical diagnosis of PHP type 1B.

Discussion

Imprinting is a complicated mechanism that involves establishment of DNA methylation at paternally and maternally ICRs during spermatogenesis and oogenesis, as well as maintenance of imprints after fertilization. Recently, several patients with hypomethylation at a range of maternally methylated ICRs have been described, including patients with BWS and imprinting defects of the GNAS complex, suggesting a more generalized imprinting disorder resulting from defects in the imprinting maintenance factors (1–5).

None of the BWS patients with hypomethylation of multiple imprinted loci (including the GNAS complex locus) described so far had disturbances of calcium homeostasis reported (3). Because this is only the third report of a patient with clinical signs and symptoms of multiple diseases related to hypomethylation of multiple imprinted loci, one could conclude that patients suffering from multiple diseases related to hypomethylation of multiple imprinted loci are extremely rare. Our patient had normal levels of calcium and PTH at initial investigation at the age of 6 months and never presented with classical signs of hypocalcemia. We therefore believe that other BWS patients with methylation abnormalities of the GNAS complex locus could well have undiagnosed subclinical hypocalcemia. Because chronic hypocalcemia and/or hyperphosphatemia can lead to serious complications (eg, intracranial calcifications, Parkinsonism, cataract, myocardial dysfunction, and prolonged QT interval), diagnosis of even subclinical hypocalcemia is important. We therefore believe that the possibility of PHP type 1B should be considered in all patients with an imprinting disorder. Baple et al (6) state that epigenetic analysis at multiple loci should be carried out in patients presenting with clinical signs that could be consistent with more than one of the classical imprinting disorders. Based on our patient with subclinical hypocalcemia, we suggest that patients with an imprinting disorder should be monitored for elevations in PTH. In case of persistent elevated PTH levels, epigenetic analysis of the GNAS complex locus should be considered.

Acknowledgments

Disclosure Summary: The authors have nothing to disclose.

Abbreviations

 
• BWS

  Beckwith-Wiedemann syndrome

 
• ICR

  imprinting control region

 
• PHP

  pseudohypoparathyroidism.

References