The proband, a Sudanese male born following normal pregnancy and delivery presented at the age of three months with abdominal distension and constipation, in the absence of a goiter or umbilical hernia. Growth was normal for height and weight at the 50th percentile. Written informed consent was obtained from the parents for blood and serum draws and analyses. Serum TSH and free thyroxine (FT4) were initially measured in Khartoum. Serum thyroid function tests (TFTs) after starting treatment including TSH, total thyroxine (TT4), total triiodothyronine (TT3), FT4, thyroxine-binding globulin (TBG), thyroglobulin (TG), thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TGAb) were completed (Immulite 1000; Siemens, Munich, Germany and by Elecsys; Roche, Switzerland). Reverse triiodothyronine (TrT3) was measured by radioimmunoassay (Adaltis Italia S.p.A, Bologna, Italy). DNA for sequencing was extracted from peripheral white blood cells using a Qiagen DNA Blood Mini Kit (Hilden, Germany). DNA from the mother and proband were sent for whole exome sequencing (Novogene, Agilent SureSelect Human All Exon V6 Kit). Whole exome sequencing (WES) results were first scanned for mutations in genes known to be related to TH synthesis or function (Supplemental Table 1). Functional prediction scores Sorting Intolerant from Tolerant (SIFT), Polyphen2 HumanDiv (HDIV) MutationTaster and Combined Annotation Dependent Depletion (CADD) were tested in silico, allele frequency, and zygosity were all considered in determining the likely cause of the CCH phenotype. The mutation was confirmed by sanger sequencing of DNA from all available family members in order to determine the mode of inheritance.
TFTs at 3 months of age revealed a TSH reported as 0.01 mIU/L (reference range 0.4-4.3 mIU/L) and low FT4 of 1.0 pmol/L (reference range 4-10.6 pmol/L). The proband had no family history of thyroid disease, however, both parents reported being first-degree cousins. The proband was diagnosed with CCH and started on levothyroxine (L-T4) treatment. Now, at eleven-year-old on subtherapeutic L-T4 replacement the TFTs demonstrated undetectable TSH on the Elecsys (<0.01) and on Immulite (<0.03) with Low FT4 (Individual II-1, Figure 1). The proband had normal neurological and psychological development on physical examination. WES found a novel missense mutation located on exon 2 of the TSHbeta, c.T141G p.C47W (numbering includes the 20 amino acid signal peptide). Sanger sequencing confirmed that both parents were heterozygous for the C47W mutation, while the proband was homozygous. The mutation was predicted by several in silico methods to have a deleterious effect (SIFT 0.0, Damaging; Polyphen2_HDIV 0.973, probably damaging; MutationTaster 1, disease causing; and CADD 3.17, 16.62). Analysis of the allele frequency in the African and general populations was not available as this is a novel mutation not located in the Genome Aggregation Database.