THRB Gene Mosaicism Confirmed by Next-Generation Sequencing in a Clinically Symptomatic Infant.

A 4-day-old infant was admitted for neonatal jaundice. He had persistent tachycardia and tachypnea. Initial workup showed a serum free T4 of 75.6 pmol/L (5.87 ng/dL) (reference range: 11.5-28.3 pmol/L; 0.89-2.20 ng/dL) and a nonsuppressed TSH 3.76 mIU/L (reference range: 0.72-11.0 mIU/L). A TRH stimulation test showed an exaggerated TSH response with a peak of 92.1 mIU/L at 30 minutes after TRH injection, which suggested the diagnosis of resistance to thyroid hormone ß syndrome. Sanger sequencing showed a questionable pathogenic variant in the THRB gene with low signal amplitude. Restriction fragment length polymorphism was consistent with its presence. The variant was originally reported as heterozygous. Next-generation sequencing was performed on blood and buccal swab samples of the patient and his parents, which confirmed this de novo mosaic variant NM_000461.5:c.1352T > C p.(Phe451Ser) in the patient but not in his asymptomatic parents. As it was in a mosaic state, only the offspring, but not other first-degree relatives, of the patient would have the risk of inheriting that variant.

Vascular Ehlers-Danlos syndrome: A null COL3A1 variant found in a patient with loin pain without marked cutaneous features (case report).

Patients with null variants may have milder vascular Ehlers-Danlos syndrome, presenting with seemingly non-specific complaints and subtle cutaneous features that may be missed. A high index of suspicion and early genetic testing (aided by next-generation sequencing) were crucial for prevention of life-threatening complications in the patient and family members.

X-chromosome inactivation and PCDH19-associated epileptic encephalopathy: A novel PCDH19 variant in a Chinese family.

BACKGROUND: Developmental and epileptic encephalopathy 9 (DEE9, MIM #300088) is an early onset seizure disorder associated with cognitive impairment and behavioral disturbances. It is caused by mutation in protocadherin 19 with an unusual X-linked inheritance selectively involving heterozygous females or mosaic hemizygous males, while hemizygous males are unaffected. Cellular interference was the postulated mechanism underlying the unusual inheritance pattern. CASE REPORT: We report a Chinese girl who presented with severe treatment refractory seizures at 26 months of age and was found heterozygous for a novel likely pathogenic missense variant NM_001184880.2:c.488T>A p.(Val163Glu) in PCDH19. Her younger sister, who was also heterozygous for the variant, was asymptomatic with normal development at the time of reporting at 37 months of age. X-chromosome inactivation study by androgen receptor gene methylation assay in DNA from peripheral leukocytes was performed which demonstrated somewhat skewed X-chromosome inactivation in the proband and extremely skewed X-chromosome inactivation in the asymptomatic younger sibling. CONCLUSION: PCDH19-related seizure disorder has incomplete penetrance and variable expressivity. Further studies are required to determine the potential role of X-chromosome inactivation on the phenotypic variability and patient outcomes. Liberal referral for PCDH19 testing among female patients with early-onset seizures should be considered to enhance case detection.