Introduction: Congenial hypothyroidism due to thyroid dysgenesis is usually regarded as sporadic. However, a small but significant proportion of familial cases have been identified (2%). Herein, we describe a case report of unusually large family of 10 siblings, out of which five were affected with congenital hypothyroidism, which is supposed to be the world’s largest series of familial congenital hypothyroidism due to thyroid dysgenesis.
Case Report: We describe a family of 10 siblings out of which five presented to endocrine department with complaints of lethargy, constipation, hoarseness of voice, edema, short stature and mental retardation. The eldest affected sibling was 25-year-old while the youngest affected child was 10-year-old. All the affected siblings had feeding difficulties, delayed fine motor, gross motor and social developmental milestones along with subnormal intelligence. On evaluation they were found to be grossly hypothyroid. Complete absence of thyroid tissue was found on ultrasonography and 99mTc pertechnetate scan.
Conclusion: Familial congenital hypothyroidism due to thyroid dysgenesis is a rare finding; timely evaluation and proper genetic counseling can prevent disastrous consequences.

Keywords: Athyreosis, Familial congenital hypothyroidism, Sibling, Thyroid dysgenesis