Familial Neonatal Hyperparathyroidism

Neonatal HPT is a rare disorder. It is usually associated with severe hypercalcemia, requiring urgent treatment. More than 50 cases of neonatal HPT have been reported in the literature.44"56'89119"126 They may be sporadic or familial. Hillman and colleagues first drew attention to the familial occurrence of neonatal HPT.119 About half of the patients with neonatal HPT have a documented familial inheritance.44"56120 121 Two types of inheritance—autosomal dominant and autosomal recessive—have been reported in neonatal HPT. The documentation of seven cases from three families suggests an autosomal recessive transmission.119"121 Other cases of neonatal HPT are associated with BFHH.

Patients with BFHH appear to have a benign course with normal survival. In contrast, children with neonatal HPT often have a poor clinical course. Pollak and associates56 demonstrated that a single defective allele causes BFHH, whereas two defective alleles cause severe neonatal HPT, and the genetic defect maps to the CASR gene on chromosome 3ql3.3-21. Genetic studies also showed that a de novo CASR gene mutation resulted in sporadic neonatal HPT,127128 and infants with a homozygous CASR gene mutation or infants with a heterozygous mutation,89'93 94 delivered by a normal mother, develop neonatal HPT.89127

At birth, newborns are usually normal in terms of size and weight. Both genders are affected. The clinical manifestations usually become evident during the first week of life but may not be recognized until 3 or 4 months of age or later.

Severe hypotonia is almost always present in children with profound hypercalcemia. Failure to thrive is common and is usually combined with digestive disorders, including constipation, anorexia, difficult feeding, vomiting, and ileus. Some infants present with dehydration, and renal stones have been reported in three infants. Advanced demineralization is present in most children, and limb and thoracic cage deformities or pathologic fractures have been reported.

At neck exploration, the parathyroid glands are diffusely enlarged and chief cell hyperplasia is evident histologically.123 Medical management, including vigorous hydration, should be instituted in all patients and may be successful in milder cases,46'51'52 although urgent parathyroidectomy is recommended for most patients with severe urgent conditions.

Because of the high recurrence rate after subtotal parathyroidectomy, total parathyroidectomy with immediate autotransplantation or with late autotransplantation of cry-opreserved parathyroid tissue is recommended. After total parathyroidectomy and parathyroid autotransplantation, some infants have modest hypercalcemia, a normal serum PTH level, hypermagnesemia, and relative hypocalciuria, similar to patients with BFHH.49 All newborns from families with BFHH must have a serum calcium determination.

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