Thyroxine-binding Globulin Deficiency Research Articles

The Mendelian inheritance of a human X chromosome-specific DNA sequence polymorphism and its use in linkage studies of genetic disease.

A recombinant DNA sequence, lambda RB6, was isolated from a human X chromosome library and shown to be X-specific by hybridisation to DNA from a human-mouse somatic cell hybrid containing X as the only human chromosome. The cloned sequence was located on the long arm distal to Xq13 using a human-mouse somatic cell hybrid containing a partial human X chromosome. DNA samples isolated from control human females were digested with the restriction enzyme MspI, and analysed by "blotting" and hybridisation to the radioactive cloned DNA. Eight of 14 individuals from a random population showed a single hybridising band 7.5 kilobase pairs (kb) in length, but six showed an additional band 10.1 kb in length. DNA from 12 members of a family with X-linked thyroxine-binding globulin deficiency was analysed for the segregation of this polymorphism. The results show that the polymorphism is inherited in a Mendelian fashion, and that the disease locus is not closely linked to the polymorphic site. Such polymorphisms will be useful as markers for chromosome mapping and for the antenatal diagnosis of genetic diseases.

Familial thyroxine-binding globulin deficiency detected in a pilot screening program for congenital hypothyroidism

During a pilot screening program for congenital hypothyroidism, performed in Italy over a three years period on 38,000 newborns, seven cases (1/5,400) of thyroxine-binding globulin (TBG) deficiency, have been detected. None of these infants was affected by any pathology or had been treated with drugs which could explain TBG deficiency as an acquired condition. Familial studies pointed out that the transmission of the defect is consistent or compatible with X-chromosome linkage.

Congenital hypothyroidism detected by a screening program with specimen collection at two time periods

The Northwest (U.S.) Regional Screening Program (NWRSP) for congenital hypothyroidism (CH) employs a primary T4 screen with TSH backup. Heel prick filter paper specimens are routinely collected at 2 time periods: days 1-7 of life and 2-6 weeks of age. Between 5/75 and 3/81, 470,750 infants were tested on the first specimen, while 266,200 were tested on the second specimen. 101 infants were detected with primary hypothyroidism (1:4660), 2 infants had hypopituitary hypothyroidism, while 78 infants were detected with congenital TBG deficiency (1:6035). Of the 101 infants, 90 were detected with a low T4 and elevated TSH on the first specimen (1:5,230), while 11 infants were discovered with a low T4 and high TSH on the second routine specimen (1:24,200). Of these 11 infants, 7 had a T4 concentration above the 3% cutoff on the initial specimen while the other 4 had a T4 below the cutoff, but their TSH concentrations were below the level of sensitivity of the TSH assay (usually <25 μU/ml). Tc99m scans done in 9 of 11 infants showed some residual thyroid tissue in 8 of 9 cases. Six of 7 infants had normal skeletal maturation on X-ray studies. We conclude that 10% of infants with CH appear to have an evolving hypothyroidism which is detected only by a second routine screening test at 2-6 weeks of age. The frequency of detection of CH on the second routine specimen has proven cost-effective in the NWRSP.

Dichotomy between serum free triiodothyronine and free thyroxine concentrations in familial thyroxine-binding globulin deficiency.

The mean serum total T4 (3.2 +/- 1.0 micrograms/100 ml) and T3 levels (83 +/- 29 ng/100 ml) in eight euthyroid patients with T4-binding globulin (TBG) deficiency from two families were significantly lower than those in either the unaffected relatives (P less than 0.05) or the control subjects (P less than 0.01). The lowest T4 and T3 values were found in the four hemizygotes (2.4 +/- 0.2 micrograms/100 ml and 69 +/- 25 ng/100 ml, respectively). In contrast to the absolute T4 and T3 levels, the mean percentages of free T4 and free T3 in the affected members were about twice as high as those in either the unaffected relatives or the controls. Despite an elevated percentage of free T4 in each of the TBG-deficient members, the mean absolute free T4 (FT4) level (0.89 +/- 0.20 ng/100 ml) was significantly lower than those in both control groups [1.31 +/- 0.2 ng/100 ml (P less than 0.02) and 1.24 +/- 0.30 ng/100 ml (P less than 0.01), respectively]. Serum FT4 levels were subnormal in three of four hemizygotes. In contrast to FT4, the mean FT3 level in the affected members (0.33 +/- 0.04 ng/100 ml) was significantly higher than that in either the nondeficient relatives (0.25 +/- 0.02 ng/100 ml; P less than 0.02) or the control subjects (0.26 +/- 0.04 ng/100 ml; P less than 0.02), whereas the ratio of FT3 to FT4 was about twice as high. The data suggest that in TBG deficiency, euthyroidism in maintained by a subtle equilibrium between low FT4 and high FT3 levels.

Transient secondary hypothyroidism and thyroxine binding globulin deficiency in leukemic children during polychemotherapy: an effect of L-asparaginase.

Recently it has been observed that L-asparaginase causes transient thyroxine binding globulin (TBG) deficiency in adults. In the present study we investigated the influence of L-asparaginase on the pituitary-thyroid axis and on the synthesis of TBG. 14 children with acute lymphoblastic leukemia were treated with a combination of L-asparaginase, vincristine, prednisone and daunomycin for remission induction. Thyroid function was monitored by measuring total T4, free T4, total T3, TSH and TBG with specific radioimmunoassays before, during and after treatment. Within 3 weeks of L-asparaginase therapy total T4 fell significantly from 10.7±1.6 to 2.9±1.8 μg/100 ml, free T4 from 1.77±0.4 to 0.94±0.35 ng/100 ml, total T3 from 0.99±0.23 to 0.35±0.2 ng/ml and TBG from 29.4±3.6 to 8.0±3.8 μg/ml. Basal TSH values tinuation of L-asparaginase, but following further treatment with other antileukemic agents, all values became normal within 2–4 weeks. In 6 patients with hypothyroid free T4 values TRH induced TSH release was totally blocked during L-asparaginase therapy. Our data clearly demonstrated that L-asparaginase caused a transient TBG deficiency. Total T4 and T3 were in the hypothyroid range because of low TBG concentrations. In addition to TBG deficiency transient, secondary hypothyroidism occurred in approximately 40–50% of all patients treated with L-asparaginase. These alterations were most likely caused by drug induced inhibition of protein synthesis. Under certain circumstances thyroid hormone replacement might be life-saving in severely ill patients suffering from transient, drug induced hypothyroidism.

Postnatal changes in thyroid hormones and hormone-binding proteins in mother and infant with TBG deficiency

Serial blood determinations of T4,T3,TSH,TBG,TBPA and albumin were made in a girl with partial TBG deficiency and her mother, who was suspected to suffer from hypothyroidism. In the girl normal se-TSH, low total se-T4 and se-T3 and a se-TBG level at 50% of normal for age and maturity were found at the 8th day of life. Se-TBPA and se-albumin value were normal. During a period of 22 months, the low se-TBG level remained unchanged; se-TBPA and albumin increased normally. Se-T3 but not se-T4 increased. In the mother the se-TBG level was (6 weeks after the delivery) similar to that of nonpregnant adults, but decreased gradually to a level, which was 50% of normal, indicating a TBG deficiency in the mother as well. A study of the family revealed 2 affected females with a se-TBG at about 50% and 3 affected males with a se-TBG at about 20% of normal level. An X-linked inheritance was suggested. The significance of the different postnatal pattern of TBG changes in mother and infant with partial TBG deficiency remains to be revealed.

Radioimmunoelectrophoretic analysis of proteins binding 3, 3', 5'-triiodothyronine in human serum.

The binding of purified 131I-3, 3', 5'-triiodothyronine (reverse T3) (rT3) to normal human serum components was investigated by a radioimmunoelectrophoretic technique. When anti-whole human serum was used, five distinct arcs of radioactivity were observed. Evidence was obtained that five of these radioactive arcs were not artifacts, but were due to components binding rT3. From the radioimmunoelectrophoretic patterns with specific antisera, five of these components were identified as thyroxine binding prealbumin, albumin, thyroxine binding globulin (TBG) and alpha 1-and beta-lipoproteins. No radioactive arc of TBG was detected in serum from a patient with TBG deficiency.

Inherited X chromosome linked thyroxine-binding globulin (TBG) deficiency in a homozygous female.

Of the 37 families with TBG deficiency so far described, 31 were shown to be compatible with X chromosome linked mode of inheritance, and in 5 of the remaining 6 this mode of transmission was suspected. Difficulties in proving X chromosome linkage in some families was usually due to the inability to identify the heterozygous female carriers when affected males were only partially TBG deficient. This work describes a new family with inherited TBG deficiency which on first glance showed inconsistencies with X chromosome linked inheritance. More specifically, there was an apparent male to male transmission of the trait and the presentation in one female of low TBG, phenotypically indistinguishable from the affected males. Studies on three generations identified TBG deficiency on both the maternal and paternal branches of the family. We were thus able to prove that the affected male inherited the trait from his heterozygous mother, rather than from his father, and that the female with more severe TBG deficiency was homozygous for the trait through acquisition of a defective X chromosome from both mother and father. The latter explained her phenotype presentation indistinguishable from that in affected hemizygous males. Thus, unless proven otherwise, all inherited TBG abnormalities in man appear to be X chromosome linked. Because of the relatively common prevalence of inherited TBG defects, marriages among such individuals are expected to give rise to a progeny with an unusual phenotypic presentation. All members of the family were clinically euthyroid and affected members showed a normal TSH response to TRH.

Thyroxine-binding globulin capacity and concentration evaluated from blood spots on filter-paper in a screening program for neonatal hypothyroidism.

We describe a simple method for evaluating thyroxine-binding globulin capacity and concentration from a single 1-cm blood spot on filter-paper used in a screening program for neonatal hypothyroidism. This method permits prompt diagnosis of about 90% of the infants with thyroxine-binding globulin deficiency in our abnormal low-thyroxine, low-thyrotropin population. There was excellent equivalence between results obtained by our method and by the method of Chopra et al. (J. Clin. Endocrinol. Metab. 35:565, 1972), and minimal overlap between the population with low thyroxine-binding globulin and the low-thyroxine, normal thyrotropin population. We recommend this method to all programs in which a primary thyroxine measurement is used in screening for congenital hypothyroidism.

Thyroxine-binding globulin capacity and concentration evaluated from blood spots on filter-paper in a screening program for neonatal hypothyroidism.

Abstract We describe a simple method for evaluating thyroxine-binding globulin capacity and concentration from a single 1-cm blood spot on filter-paper used in a screening program for neonatal hypothyroidism. This method permits prompt diagnosis of about 90% of the infants with thyroxine-binding globulin deficiency in our abnormal low-thyroxine, low-thyrotropin population. There was excellent equivalence between results obtained by our method and by the method of Chopra et al. (J. Clin. Endocrinol. Metab. 35:565, 1972), and minimal overlap between the population with low thyroxine-binding globulin and the low-thyroxine, normal thyrotropin population. We recommend this method to all programs in which a primary thyroxine measurement is used in screening for congenital hypothyroidism.

Measurement of triiodothyronine in urine.

A radioimmunoassay procedure to measure triiodothyronine (T3) in unextracted urine is described. One hundred microliter of T3 standards or samples were incubated with 100 microliter of T3 antiserum (1:40,000), 100 microliter of tracer 125I-T3 and 700 microliter of 0.05 M borate buffer, pH 8.6. Separation of free from bound antigen was achieved by dextran coated charcoal. The cross-reaction of L-T3 with L-T4 in this assay system was less than 0.2%. Dilution of high T3 urine was parallel to the standard curve. Recovery was 101 +/- 8%. Coefficients of variation were 3-8% within each assay and 13% between assays. Euthyroid subjects excreted 0.81 +/- 0.39 microgram (mean +/- S.D.) in 24 hr. Similar values were obtained in pregnant women, euthyroid patients with chronic thyroiditis, and a patient with thyroxine-binding globulin deficiency. Excretion of urinary T3 was high (7.48 +/- 3.32 microgram/24 h) in patients with hyperthyroidism, and low (0.14 +/- 0.15 microgram/24 hr) in patients with hypothyroidism. Urinary T3 excretion was almost undetectable in terminal renal failure. Positive correlations were found between urinary T3 and serum total T3 (r = 0.89) and especially serum free T3 (r - 0.97). A positive correlation was also found between urinary T3 and creatinine clearance (r = 0.63). Mean urinary clearance of T3(CT3=Urinary T3 excretion/serum free T3 was 166 ml/min and was significantly higher than their mean creatinine clearance (110 ml/min). The measurement of T3 in urine is reliable and easy to perform, and may allow a new approach to the understanding of thyroid hormone metabolism.

The method of T4 radioimmunoassay using filter paper blood samples and its application for the early detection of neonatal hypothyroidism (author's transl)

We examined the method of radioimmunoassay of the Disc T4 (dried blood spot T4) for the purpose of mass screening of neonatal hypothyroidism and tried the parallel assay of T4 and TSH in dried blood spotted on filter paper at the fifth day of life, and we compared the results. By changing the volumes of T4 antibody and T4 antigen solutions, it is possible to measure thyroxine using two discs 3mm in diameter. Disc T4 values obtained in 45 unknown samples by this method were in good correlation with serum T4 values of the same subjects (Y = 0.97X + 0.06). The coefficients of variation were 5.6 to 18.9% in the range of 5.3 to 10.7 micrograms/100ml of Disc T4 (within assay), and 7.9 to 20.8% in the range of 2.4 to 10.3 micrograms/100ml of Disc T4 (between assay). We measured both Disc T4 and Disc TSH of 26,067 newborn infants born between June 1978 and May 1979. Out of 26,067 measurements, four cases of primary hypothyroidism, fourteen cases of TBG deficiency and two cases of transient hypothyroidism were discovered. Out of the four cases of primary hypothyroidism, three showed low Disc T4 (1.3 to 4.0 micrograms/100ml) and high Disc TSH (200 to 240 micromicrons/ml), one showed normal Disc T4 (7.1 micrograms/100ml) and high Disc TSH (30 micromicrons/ml). It was thought the last case might be mild hypothyroidism. In 14 cases of TBG deficiency, Disc T4 was not detectable to 3.4 micrograms/100ml while Disc TSH was within the normal range. In two cases of transient hypothyroidism, Disc T4 measurements showed normal range (6.5, 10.6 micrograms/100ml), and Disc TSH showed high values (41, 120 micromicrons/ml). Therefore, Disc TSH was more sensitive and showed less false positive cases than did Disc T4 for screening hypothyroidism. Although no secondary hypothyroidism existed in the 26,067 measurements, it continues to be important to measure Disc T4 for the discovery of secondary or tertiary hypothyroidism.

Thyroxine-binding globulin deficiency in Beckwith syndrome

swelling because of the osmotic activity of intracellular galactitol. With a block in galactose metabolism due to defective galactokinase activity, there is little or no formation of galactose-l-phosphate, so that the formation of galactitol and its excretion in the urine is the main route of galactose metabolism. ~ In classic galactosemia resulting from galactose-l-phosphate uridyl transferase deficiency, in which mental retardation and other symptoms are regularly seen in untreated patients, there is the accumulation of galactose-1-phosphate in addition to galactitol. It has been reasonable to assume that the symptoms other than cataracts are a consequence of the formation of large amounts of galactose-1-phosphate. If the mental retardation in our patients is a manifestation of the galactokinase deficiency, then the accumulation of galactose itself or of galactitol must play an etiologic role. The complete elucidation of the clinical spectrum of galactokinase deficiency must await the observation of greater numbers of patients. Since all infants and young children with cataracts should be examined for galactokinase deficiency 1~ and, when found, treated with a galactose free diet, the number of undiagnosed older children, such as we report here, should be few. The possibility that untreated patients may be mentally retarded adds a compelling reason for maintenance of stringent dietary therapy. REFERENCES 1. Segal S: Galactosemia, in Stanbury JB, Wyngaarden JB, and Fredrickson DS, editors: The metabolic basis of inherited disease, ed 4, New York, 1978, McGraw-Hill Book Company, Inc., pp 160-181. 2. Gitzelmann R: Deficiency of erythrocyte galactokinase in a patient with galactose diabetes, Lancet 2:670, 1965. 3. Ng WG, Donnell GN, and Bergren WR: Galactokinase activity in human erythrocytes of individuals at different ages, J Lab Clin Med 66:115, 1965. 4. Ng WG, Bergren WR, and Donnell GW: An improved procedure for the assay of hemolysate galactose-l-phosphate uridyltransferase activity by the use of labeled galactose-l-phosphate, Clin Chim Acta 15:489, 1967. 5. Pickering WR, and Howell RR: Galactokinase deficiency: Clinical and biochemical findings in a new kindred, J PEDIATR 81:50, 1972. 6. Gitzelmann R: Hereditary galactokinase deficiency, a newly recognized cause of juvenile cataracts, Pediatr Res 1:14, 1967. 7. Litman N, Kanter A, and Finberg L: Galactokinase deficiency presenting as pseudotumor cerebri, J PEDIATR 86:410, 1975. 8. Cogan DD: The lens, cataracts and galactosemia, N Engl J Med 288:1240, 1973. 9. Quan-Ma R, and Wells W: The distribution ofgalactitol in tissues of rats fed galactose, Biochem Biophys Res Commun 20:486, 1965. 10. Beutler E, Matsumoto F, Kuhl W, Krill A, Levy N, Sparkes R, and Degnan M: Galactokinase deficiency as a cause of cataracts, N Engl J Med 288:1203, 1978.

Neonatal screening for hypothyroïdism by simultaneous determination of T4 and TSH on filter paper

A simultaneous determination of T4 and TSH has been done on 53.000 new borns since January 1st of 1977 in the Midi-Pyrénées district. 18 cases of hypothyroïdism have been detected, an incidence of 1/2950 new borns. TSH values always were above 80 μU/ml ; T4 values are under m -2 σ in 14 cases, normal in 2 cases (8,8 and 9 μg/dl) and between -1 and -2 σ in 2 cases. A thyroid scanning with 123 iodine or 99 Tech. has shown the absence of thyroid in 8 cases, an ectopic gland in 8 cases and a thyroid in a normal position in one case. A treatment has been possible before the first month of life in each case. The average D.Q. for the seven oldest new borns (m = 11 months) is 96. The simultaneous determination of T4 and TSH is a sensitive and specific screening method for hypothyroidism. False-negative are avoided and the number of false-positive results is reduced. All cases of hypothyroidism can be detected (primary hypothyroïdism, hypothalamo-hypopituitary hypothyroïdism, TBG deficiency, etc. . .). Then, an early and certain diagnosis is made possible (T4 low and TSH increased).

Acute deficiency of thyroxine-binding globulin during L-asparaginase therapy.

ESCHERICHIA COLI L-asparaginase, an antileukemic agent, acts by hydrolyzing plasma L-asparagine to L-aspartic acid and ammonia, resulting in depletion of plasma L-asparagine levels.1 , 2 Cells susc...

Screening of newborn infants for hypothyroidism. Two years' experience in South Autralia.

Over a period of two years, 40,000 newborn infants in South Australia have been screened for congenital hypothyroidism by the measurement of thyroxine and, on selected samples, of thyroid stimulating hormone. Samples were those obtained for an established newborn screening programme in the State. Eight infants with hypothyroidism were detected; in seven, this was due to congenital agenesis of the thyroid gland and one infant had residual thyroid tissue. A further three sick infants had abnormalities of thyroid function; in two, this was transient and reverted to normal after several weeks and the third infant died. Three infants had thyroxine-binding globulin deficiency.

Screening for congenital hypothyroidism: Results of screening one million North American infants

Pilot programs for screening of newborn infants for congenital hypothyroidism began in North America in 1972. To date, the five oldest programs (Quebec, Pittsburgh, Toronto, Oregon Regional, and New England Regional) have screened 1,046,362 infants. A total of 277 infants with congenital hypothyroidism have been detected and seven have been missed, resulting in a total of 284 affected infants in the screened population and an overall incidence of one in 3,684 live births. Of the affected infants, 246 were determined to have primary hypothyroidism, an incidence of one in 4,254 births. Ten infants with secondary-tertiary hypothyroidism were detected in Quebec, Oregon, and Toronto, an incidence of one in 68,200 births. Of all the infants with primary hypothyroidism who were adequately studied, 63% were determined to have aplastic or hypoplastic glands, 14% normal or enlarged glands, and 23% ectopic thyroid tissue. The estimated minimum incidence of infants with TBG deficiency is one in 8,913 births. Only 8 of the 277 detected infants were suspected clinically to have congenital hypothyroidism prior to the time of confirmation of the diagnosis at 4 to 8 weeks of age. The cost of screening varied from $0.70 to $1.60 per infant, depending on which costs were included in the estimate. Preliminary evidence from Quebec suggests that infants treated in the program have normal developmental testing scores at 18 months of age.

Familial thyroxine-binding globulin deficiency in association with non-toxic goitre.

A kindred is presented in which 4 members in 3 generations showed absent or reduced serum concentrations of thyroxine-binding globulin (TBG). TBG was undetectable by radioimmunoassay in one male and decreased to varying extent in 3 female patients (4.0, 4.2 and 8.6 microgram/ml; normal range 12.5--26.0 microgram/ml). Total thyroxine serum concentrations in the affected subjects were well in the hypothyroid range without clinical evidence of hypothyroidism. The mode of transmission of the trait was consistent with X-chromosome linkage. A high incidence of non-toxic goitre was also present in most of the family members examined irrespective of TBG levels. The transmission of the goitre trait was compatible with autosomal dominant inheritance. Thus its association with transmission of TBG deficiency was interpreted as not causal but coincidental.

Neonatal Hypothyroidism Detected by the Northwest Regional Screening Program

The Northwest Regional Screening Program to detect congenital hypothyroidism in infants born in Oregon, Montana, Alaska, and Idaho (combined birthrate of 69,000/ yr) was added to our ongoing screening program in 1975. The program utilizes dried blood filter paper specimens collected routinely in the first few days of life in all four states and again at about 6 weeks of age in Oregon only. The screening test consist of an initial thyroxine (T4) measurement; a thyroid-stimulating hormore (TSH) determination is performed on those specimens with T4 concentrations in the lowest 3% group. Serum samples obtained by venipuncture are requested for confirmation of the diagnosis. In the first two years of the program, 25 infants with primary hypothyroidism were detected amont 110,667 infants screened, a frequency of 1:4,430. Fourteen cases of thyroxine-binding globulin deficiency were also detected, a frequency of 1:7,900. Using the T4 followed by TSH testing approach, the frequency of request for repeat specimens was 0.4% in Oregon and 0.05% in the other states. The cost per specimen was $1.96. The majority of infants lacked clinical signs or symptoms of hypothyroidism; only one infant was clinically suspected of having hypothyroidism prior to detection. The most common neonatal symptoms were constipation, lethargy, and prolonged jaundice, while the most common physical signs were hypotonia, umbilical hernia, and large fontanels. Thyroid scans showed the most common etiology to be thyroid aplasia, followed by an ectopic gland, hypoplasia, and goiter. Serum T4 concentrations were lowest in those infants with aplasia, intermediate in infants with an ectopic gland or hypoplasia, and normal in the infant with the goiter. Neonatal hypothyroidism varies in degree and has several different causes; the capacity to secrete thyroid hormone, the duration before hypothyroidism becomes clinically manifest, and possibly the eventual prognosis for intellectual function depend on the nature of the underlying cause. While the mean age at treatment was 59 days, the goal of diagnosing congenital hypothyroidism and treating affected infants by 1 month of age seems realistic.

Screening for neonatal hypothyroidism in South Australia

Neonatal hypothyroidism is difficult to detect by clinical examination of the newborn baby. Undetected, it usually results in mental and physical retardation. The earlier the diagnosis is made, and treatment instituted, the better the outlook for normal development. Screening for low thyroxine levels was carried out using a modified Larsen radioimmunoassay method on a 3 mm disc of chromatography paper on which blood samples had been collected by heel stab at 5 days of age. This programme was commenced in February 1977. By April 1977, a T.S.H. method (Phadebas kit) was introduced using an 8 mm blood spot. The samples selected for T.S.H. measurement were those in the lowest 10th percentile of each thyroxine screen batch. The incorporation of the T.S.H. screen greatly reduced the number of patients recalled from 1% to 1 in 2500. By August 1978, approximately 30,000 newborns had been screened. In this sample, 5 cases of primary neonatal hypothyroidism and 3 cases of thyroxine binding globulin deficiency had been detected. Neonatal hypothyroidism is difficult to detect by clinical examination of the newborn baby. Undetected, it usually results in mental and physical retardation. The earlier the diagnosis is made, and treatment instituted, the better the outlook for normal development. Screening for low thyroxine levels was carried out using a modified Larsen radioimmunoassay method on a 3 mm disc of chromatography paper on which blood samples had been collected by heel stab at 5 days of age. This programme was commenced in February 1977. By April 1977, a T.S.H. method (Phadebas kit) was introduced using an 8 mm blood spot. The samples selected for T.S.H. measurement were those in the lowest 10th percentile of each thyroxine screen batch. The incorporation of the T.S.H. screen greatly reduced the number of patients recalled from 1% to 1 in 2500. By August 1978, approximately 30,000 newborns had been screened. In this sample, 5 cases of primary neonatal hypothyroidism and 3 cases of thyroxine binding globulin deficiency had been detected.