Maternal Uniparental Disomy for Chromosome 20: Physical and Endocrinological Characteristics of Five Patients

Maternal uniparental disomy for chromosome 20 [UPD(20)mat], resulting in aberrant expression of imprinted transcripts at the GNAS locus, is a poorly characterized condition. These patients manifested a phenotype similar to that of Silver-Russell syndrome (SRS) and small for gestational age-short stature (SGA-SS); however, the etiological relationship between UPD(20)mat and SRS/SGA-SS remains unclear. Moreover, no report has described endocrinological assessment of UPD(20)mat patients, although paternal UPD(20), the mirror image entity of UPD(20)mat, is known to cause multiple hormone resistance reflecting reduced α-subunit of the stimulatory G protein expression.

Patients 1 to 5 showed nonmosaic heterodisomy and/or isodisomy for the entire chromosome 20. Patients 1 to 3 and 4 were identified through UPD(20)mat screening for 55 patients with etiology-unknown SRS and 96 patients with SGA-SS, respectively. Patient 5 was identified through molecular analysis for patients with developmental defects. Patients 1 to 5 manifested postnatal growth failure and feeding problems, with or without developmental delay, and other clinical features. Patients 1 to 4 were born SGA. Patients 4 and 5 exhibited hypercalcemia and low or low-normal parathyroid hormone levels. Patient 1 showed constantly decreased thyroid-stimulating hormone (TSH) levels after 12 years of age, although she had a normal TSH level at 5.2 years of age.

The results suggest that UPD(20)mat underlies growth failure and feeding problems with additional features and could account for >5% of etiology-unknown SRS and small percentages of SGA-SS. Most important, this study provides an indication that UPD(20)mat can be associated with hypersensitivity of hormone receptors, which may gradually develop with age.