Congenital hypothyroidism (CH) is the most common endocrine disorder in children. Thyroid hormone is important for growth and intellectual development of children and thyroid hormone deprivation results in deleterious effects on bone growth [1]. Infants with CH who are not treated with levothyroxine (L-T4) have disordered and delayed epiphyseal development and grow poorly [2,3].

Newborn screening for CH using dried blood spot sampling that started in the 1970s in most of the developed Countries and in the early 1990s in Korea enabled early diagnosis and treatment of CH [4,5]. Many studies have shown that early treatment of CH leads to normalization of cognitive development [6-8]. The linear growth of patient with CH has been examined in several studies [1,9-13], but there are few studies about the final growth of patient with CH [14-17]. Furthermore there is no report regarding the growth of Korean patients with CH.

The factors that affect the final height (FH) of CH patient are also controversial. Salerno et al. [14] reported that the FH of Italian patients with CH were normal, and the FH was not correlated with the severity of CH at diagnosis, L-T4 dosage at the beginning of treatment, or etiology of the defect. Similarly, Adachi et al. [15] also documented that the FH of Japanese patient with CH was normal and there was no relationships between the FH and the etiology of CH, severity of CH (Thyrotropin [TSH] level at the start of treatment and current L-T4 dose), time of therapy initiation and adequacy of treatment during the first year of life. However, Bain and Toublanc [16] reported the main factors for a taller FH than TH were the age at the start of L-T4 treatment and the quality of treatment. They reported that the patients with taller FH than TH had a significantly younger mean age at the start of treatment than the patients with smaller FH than TH (24.8±13.5 vs. 42.8±47.3, P=0.004). Heidari et al. [18] also emphasized the importance of the first therapeutic L-T4 dosage, age at onset of treatment and age at the first free T4 normalization for anthropometric development based on a longitudinal study of 760 neonates born in 2002–2009, with CH diagnosed by neonatal screening in Iran.

Thus, this study investigated the FH in Korean patients with CH detected by newborn screening, and examined the factors that may affect the height outcome.

The newborn screening programs for CH started in the 1970s enabled early detection and treatment of CH. Newborn screening programs for CH have been highly successful in improving both cognitive and growth outcome. Several studies reported that early diagnosis and treatment of CH prevents poor growth due to hypothyroidism [9-10,13]. Grant [10] reported that height, weight and body mass index of 361 patients with CH aged 3–4 years old were normal. Moschini et al. [13] observed 42 patients who had been diagnosed with CH by newborn screening program and reported the height, weight and head circumference of the patients were in 50th–75th percentile at 6 years of age, if the treatment was initiated within 33 days after birth.

Salerno et al. [14] studied 55 Italian patients with CH. The patients were diagnosed with CH at 25±5 days of age by the newborn screening program. The height of the patients at 17±5 years old was normal (standard deviation score, 0.1±1.1) and the FH was not affected by the birth date, the age at diagnosis and the starting LT4 dose. Adachi et al. [15] reported the FH of 27 Japanese patients with CH who started L-T4 treatment at the age of 23.9±10.8 days and the FH in CH patients detected by neonatal screening. They reported that the FH of patients with CH were equivalent to TH and as long as early intervention and satisfactory management are ensured, severe CH does not appear to worsen the outcome. Likewise, in support of these previous studies, the current study of Korean patients with CH had no difference between their FH and TH, and also had no difference between the FH and height of Korean reference population.

However, Delvecchio et al. [17] reported that the FH of 215 Italian patients with CH were taller than their TH which was attributed to an improvement in the FH of Italian people over the last 20 years. Bain and Toublanc [16] also reported that patients with CH reached a taller FH than their TH. They concluded that the initial severity of the CH was not a prognostic factor for the FH, whereas the age at start of treatment was significant. They reported that the patients who exceeded their TH had an earlier start of treatment versus children who failed to reach their TH (24.8±13.5 days vs. 42.0±47.3 days, P=0.004). The discrepancy between these previous studies and our findings highlight the need for further research to conclusively identify the prognostic factors for the FH of patients with CH.

In 2012, Seth et al. [21] reported about characteristics of delayed diagnosed patients with CH. They studied 94 Indian patients with hypothyroidism who diagnosed beyond 5 years of age and 34 of the patients (36.1%) were CH. In their study, all the patients with CH who diagnosed beyond 5 years of age had growth failure and they emphasized the importance of early detection and treatment of patients with CH by newborn screening program.

In this study, we could not find information about the puberty onset and the other hormone serum levels that can influence the FH. Further research including these points is needed to evaluate factors affecting the growth of patients with CH.

In conclusion, as long as early intervention and satisfactory management are performed, the CH does not appear to worsen the growth of Korean patients with CH. And the etiology of CH, initial TSH, initial free T4 level and the time of therapy initiation do not affect the FH in CH patients. Thus, it is important to detect early and provide proper management to patients with CH by newborn screening program.