Mutations in FGF17, IL17RD, DUSP6, SPRY4, and FLRT3 are identified in individuals with congenital hypogonadotropic hypogonadism.

Congenital hypogonadotropic hypogonadism (CHH) and its anosmia-associated form (Kallmann syndrome [KS]) are genetically heterogeneous. Among the >15 genes implicated in these conditions, mutations in FGF8 and FGFR1 account for ~12% of cases; notably, KAL1 and HS6ST1 are also involved in FGFR1 signaling and can be mutated in CHH. We therefore hypothesized that mutations in genes encoding a broader range of modulators of the FGFR1 pathway might contribute to the genetics of CHH as causal or modifier mutations. Thus, we aimed to (1) investigate whether CHH individuals harbor mutations in members of the so-called "FGF8 synexpression" group and (2) validate the ability of a bioinformatics algorithm on the basis of protein-protein interactome data (interactome-based affiliation scoring [IBAS]) to identify high-quality candidate genes. On the basis of sequence homology, expression, and structural and functional data, seven genes were selected and sequenced in 386 unrelated CHH individuals and 155 controls. Except for FGF18 and SPRY2, all other genes were found to be mutated in CHH individuals: FGF17 (n = 3 individuals), IL17RD (n = 8), DUSP6 (n = 5), SPRY4 (n = 14), and FLRT3 (n = 3). Independently, IBAS predicted FGF17 and IL17RD as the two top candidates in the entire proteome on the basis of a statistical test of their protein-protein interaction patterns to proteins known to be altered in CHH. Most of the FGF17 and IL17RD mutations altered protein function in vitro. IL17RD mutations were found only in KS individuals and were strongly linked to hearing loss (6/8 individuals). Mutations in genes encoding components of the FGF pathway are associated with complex modes of CHH inheritance and act primarily as contributors to an oligogenic genetic architecture underlying CHH.

A genetic basis for functional hypothalamic amenorrhea.

BACKGROUND: Functional hypothalamic amenorrhea is a reversible form of gonadotropin-releasing hormone (GnRH) deficiency commonly triggered by stressors such as excessive exercise, nutritional deficits, or psychological distress. Women vary in their susceptibility to inhibition of the reproductive axis by such stressors, but it is unknown whether this variability reflects a genetic predisposition to hypothalamic amenorrhea. We hypothesized that mutations in genes involved in idiopathic hypogonadotropic hypogonadism, a congenital form of GnRH deficiency, are associated with hypothalamic amenorrhea. METHODS: We analyzed the coding sequence of genes associated with idiopathic hypogonadotropic hypogonadism in 55 women with hypothalamic amenorrhea and performed in vitro studies of the identified mutations. RESULTS: Six heterozygous mutations were identified in 7 of the 55 patients with hypothalamic amenorrhea: two variants in the fibroblast growth factor receptor 1 gene FGFR1 (G260E and R756H), two in the prokineticin receptor 2 gene PROKR2 (R85H and L173R), one in the GnRH receptor gene GNRHR (R262Q), and one in the Kallmann syndrome 1 sequence gene KAL1 (V371I). No mutations were found in a cohort of 422 controls with normal menstrual cycles. In vitro studies showed that FGFR1 G260E, FGFR1 R756H, and PROKR2 R85H are loss-of-function mutations, as has been previously shown for PROKR2 L173R and GNRHR R262Q. CONCLUSIONS: Rare variants in genes associated with idiopathic hypogonadotropic hypogonadism are found in women with hypothalamic amenorrhea, suggesting that these mutations may contribute to the variable susceptibility of women to the functional changes in GnRH secretion that characterize hypothalamic amenorrhea. Our observations provide evidence for the role of rare variants in common multifactorial disease. (Funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development and others; ClinicalTrials.gov number, NCT00494169.).

Oligogenic basis of isolated gonadotropin-releasing hormone deficiency.

Between the genetic extremes of rare monogenic and common polygenic diseases lie diverse oligogenic disorders involving mutations in more than one locus in each affected individual. Elucidating the principles of oligogenic inheritance and mechanisms of genetic interactions could help unravel the newly appreciated role of rare sequence variants in polygenic disorders. With few exceptions, however, the precise genetic architecture of oligogenic diseases remains unknown. Isolated gonadotropin-releasing hormone (GnRH) deficiency caused by defective secretion or action of hypothalamic GnRH is a rare genetic disease that manifests as sexual immaturity and infertility. Recent reports of patients who harbor pathogenic rare variants in more than one gene have challenged the long-held view that the disorder is strictly monogenic, yet the frequency and extent of oligogenicity in isolated GnRH deficiency have not been investigated. By systematically defining genetic variants in large cohorts of well-phenotyped patients (n = 397), family members, and unaffected subjects (n = 179) for the majority of known disease genes, this study suggests a significant role of oligogenicity in this disease. Remarkably, oligogenicity in isolated GnRH deficiency was as frequent as homozygosity/compound heterozygosity at a single locus (2.5%). Among the 22% of patients with detectable rare protein-altering variants, the likelihood of oligogenicity was 11.3%. No oligogenicity was detected among controls (P < 0.05), even though deleterious variants were present. Viewing isolated GnRH deficiency as an oligogenic condition has implications for understanding the pathogenesis of its reproductive and nonreproductive phenotypes; deciphering the etiology of common GnRH-related disorders; and modeling the genetic architecture of other oligogenic and multifactorial diseases.

Reversal of idiopathic hypogonadotropic hypogonadism.

BACKGROUND: Idiopathic hypogonadotropic hypogonadism, which may be associated with anosmia (the Kallmann syndrome) or with a normal sense of smell, is a treatable form of male infertility caused by a congenital defect in the secretion or action of gonadotropin-releasing hormone (GnRH). Patients have absent or incomplete sexual maturation by the age of 18. Idiopathic hypogonadotropic hypogonadism was previously thought to require lifelong therapy. We describe 15 men in whom reversal of idiopathic hypogonadotropic hypogonadism was sustained after discontinuation of hormonal therapy. METHODS: We defined the sustained reversal of idiopathic hypogonadotropic hypogonadism as the presence of normal adult testosterone levels after hormonal therapy was discontinued. RESULTS: Ten sustained reversals were identified retrospectively. Five sustained reversals were identified prospectively among 50 men with idiopathic hypogonadotropic hypogonadism after a mean (+/-SD) duration of treatment interruption of 6+/-3 weeks. Of the 15 men who had a sustained reversal, 4 had anosmia. At initial evaluation, 6 men had absent puberty, 9 had partial puberty, and all had abnormal secretion of GnRH-induced luteinizing hormone. All 15 men had received previous hormonal therapy to induce virilization, fertility, or both. Among those whose hypogonadism was reversed, the mean serum level of endogenous testosterone increased from 55+/-29 ng per deciliter (1.9+/-1.0 nmol per liter) to 386+/-91 ng per deciliter (13.4+/-3.2 nmol per liter, P<0.001), the luteinizing hormone level increased from 2.7+/-2.0 to 8.5+/-4.6 IU per liter (P<0.001), the level of follicle-stimulating hormone increased from 2.5+/-1.7 to 9.5+/-12.2 IU per liter (P<0.01), and testicular volume increased from 8+/-5 to 16+/-7 ml (P<0.001). Pulsatile luteinizing hormone secretion and spermatogenesis were documented. CONCLUSIONS: Sustained reversal of normosmic idiopathic hypogonadotropic hypogonadism and the Kallmann syndrome was noted after discontinuation of treatment in about 10% of patients with either absent or partial puberty. Therefore, brief discontinuation of hormonal therapy to assess reversibility of hypogonadotropic hypogonadism is reasonable. (ClinicalTrials.gov number, NCT00392756 [ClinicalTrials.gov].).

Mutations in prokineticin 2 and prokineticin receptor 2 genes in human gonadotrophin-releasing hormone deficiency: molecular genetics and clinical spectrum.

CONTEXT: Mice deficient in prokineticin 2(PROK2) and prokineticin receptor2 (PROKR2) exhibit variable olfactory bulb dysgenesis and GnRH neuronal migration defects reminiscent of human GnRH deficiency. OBJECTIVES: We aimed to screen a large cohort of patients with Kallmann syndrome (KS) and normosmic idiopathic hypogonadotropic hypogonadism (IHH) for mutations in PROK2/PROKR2, evaluate their prevalence, define the genotype/phenotype relationship, and assess the functionality of these mutant alleles in vitro. DESIGN: Sequencing of the PROK2 and PROKR2 genes was performed in 170 KS patients and 154 nIHH. Mutations were examined using early growth response 1-luciferase assays in HEK 293 cells and aequorin assays in Chinese hamster ovary cells. RESULTS: Four heterozygous and one homozygous PROK2 mutation (p.A24P, p.C34Y, p.I50M, p.R73C, and p.I55fsX1) were identified in five probands. Four probands had KS and one nIHH, and all had absent puberty. Each mutant peptide impaired receptor signaling in vitro except the I50M. There were 11 patients who carried a heterozygous PROKR2 mutation (p.R85C, p.Y113H, p.V115M, p.R164Q, p.L173R, p.W178S, p.S188L, p.R248Q, p.V331M, and p.R357W). Among them, six had KS, four nIHH, and one KS proband carried both a PROKR2 (p.V115M) and PROK2 (p.A24P) mutation. Reproductive phenotypes ranged from absent to partial puberty to complete reversal of GnRH deficiency after discontinuation of therapy. All mutant alleles appear to decrease intracellular calcium mobilization; seven exhibited decreased MAPK signaling, and six displayed decreased receptor expression. Nonreproductive phenotypes included fibrous dysplasia, sleep disorder, synkinesia, and epilepsy. Finally, considerable variability was evident in family members with the same mutation, including asymptomatic carriers. CONCLUSION: Loss-of-function mutations in PROK2 and PROKR2 underlie both KS and nIHH.

Muscle fiber size and function in elderly humans: a longitudinal study.

Cross-sectional studies are likely to underestimate age-related changes in skeletal muscle strength and mass. The purpose of this longitudinal study was to assess whole muscle and single muscle fiber alterations in the same cohort of 12 older (mean age: start of study 71.1+/-5.4 yr and end of study 80+/-5.3 yr) volunteers (5 men) evaluated 8.9 yr apart. No significant changes were noted at follow-up in body weight, body mass index, and physical activity. Muscle strength, evaluated using isokinetic dynamometry, and whole muscle specific force of the knee extensors were significantly lower at follow-up. This was accompanied by a significant reduction (5.7%) in cross-sectional area of the total anterior muscle compartment of the thigh as evaluated by computed tomography. Muscle histochemistry showed no significant changes in fiber type distribution or fiber area. Experiments with chemically skinned single muscle fibers (n=411) demonstrated no change in type I fiber size but an increase in IIA fiber diameter. A trend toward an increase in maximal force in both fiber types was observed. Maximum unloaded shortening velocity did not change. In conclusion, single muscle fiber contractile function may be preserved in older humans in the presence of significant alterations at the whole muscle level. This suggests that surviving fibers compensate to partially correct muscle size deficits in an attempt to maintain optimal force-generating capacity.

Interplay between dose and frequency of GnRH administration in determining pituitary gonadotropin responsiveness.

BACKGROUND/AIMS: The dose, frequency and contour of GnRH stimulation of the pituitary gonadotrope have been shown to be independent variables influencing pituitary LH secretion. The dynamic interaction between these variables during physiological and pathophysiological states has yet to be examined. METHODS: Twelve men with GnRH deficiency and idiopathic hypogonadotropic hypogonadism undergoing GnRH therapy participated in a series of studies in which 2 log orders of GnRH doses (2.5-250 ng/kg) were administered at frequencies varying from 0.5 to 8 hourly. Pituitary responses were characterized by pulse amplitudes and nadirs. The relative sensitivity of the gonadotrope to GnRH was defined as that dose of GnRH capable of eliciting an LH pulse amplitude equal to the mean LH amplitude in normal men. RESULTS: As GnRH stimulation of the gonadotrope slowed from 0.5 to 8 hourly, pulse amplitudes of LH increased whereas mean nadirs decreased (p < 0.05). Unique, curvilinear dose-response curves were found for each frequency that demonstrated an increasing slope (p < 0.03) as the frequency of GnRH stimulation slowed. Thus, the relative sensitivity of the gonadotrope increased as the frequency of GnRH stimulation decreased over the range of physiological frequencies tested. CONCLUSIONS: We conclude that a delicate interplay exists between the dose and frequency of GnRH stimulation of the gonadotrope that determines pituitary LH gonadotropin responsiveness in the human. Slower frequencies favor increased LH release largely due to decreasing LH nadirs and improved sensitivity of the gonadotropes to GnRH stimulation.

Longitudinal changes in body composition in older men and women: role of body weight change and physical activity.

BACKGROUND: Estimates of body-composition change in older adults are mostly derived from cross-sectional data. OBJECTIVE: We examined the natural longitudinal patterns of change in fat-free mass (FFM) and fat mass (FM) in older adults and explored the effect of physical activity, weight change, and age on these changes. DESIGN: The body composition measured by hydrodensitometry and the level of sports and recreational activity (SRA) of 53 men and 78 women with a mean (+/-SD) initial age of 60.7 +/- 7.8 y were examined on 2 occasions separated by a mean (+/-SD) time of 9.4 +/- 1.4 y. RESULTS: FFM decreased in men (2.0% per decade) but not in women, whereas FM increased similarly in both sexes (7.5% per decade). Levels of SRA decreased more in men than in women over the follow-up period. Baseline age and level of SRA were inversely and independently associated with changes in FM in women only. Neither age nor level of SRA was associated with changes in FFM in men or women. Weight-stable subjects lost FFM. FFM accounted for 19% of body weight in those who gained weight, even in the presence of decreased levels of SRA. Loss of FFM (33% of body weight) was pronounced in those who lost weight, despite median SRA levels >4184 kJ/wk. CONCLUSIONS: On average, FM increased; however, the increase in women was attenuated with advancing age. The decrease in FFM over the follow-up period was small and masked the wide interindividual variation that was dependent on the magnitude of weight change. The contribution of weight stability, modest weight gains, or lifestyle changes that include regular resistance exercise in attenuating lean-tissue loss with age should be explored.

Anthropometric assessment of 10-y changes in body composition in the elderly.

BACKGROUND: An increased central distribution of fat with advancing age is associated with chronic metabolic and cardiovascular abnormalities. Little is known about the magnitude or pattern of fat distribution and its association with healthy aging. OBJECTIVE: This study describes approximately 10-y changes in body composition at 11 anthropometric sites in elderly persons and the metabolic and physical activity factors associated with these changes. DESIGN: Skinfold thicknesses, girths, body fat by hydrodensitometry, physical activity by questionnaire, and metabolic variables were examined twice, 9.4 +/- 1.4 y apart, in 54 men and 75 women aged 60.4 +/- 7.8 y at baseline. RESULTS: Subcutaneous fat declined (-17.2%; P < 0.001), whereas total fat mass increased (7.2%; P < 0.05). Waist and hip circumference changes were the best anthropometric predictors of total fat mass change (r(2) = 0.40-0.65, P < 0.0001). Thigh girth change was more strongly associated with fat-free mass change (r(2) = 0.22, P < 0.01) than with fat mass change (r(2) = 0.07, P < 0.05) in women. An increase in physical activity was associated with an attenuation of thigh girth decline in men and women (F ratio = 5.13, P < 0.007). Traditional metabolic markers of visceral adiposity (triacylglycerol, glucose, and total cholesterol) were not significantly related to the change in waist circumference. CONCLUSIONS: Skinfold thicknesses cannot be used to assess changes in body fat mass because of age-related fat redistribution. Higher levels of physical activity can attenuate the decline in appendicular lean tissue expected over 10 y. Waist and thigh girths, rather than skinfold thicknesses, should be considered for use in longitudinal studies in the elderly because the changes in these girths capture increased abdominal adiposity and sarcopenia, respectively.

Olfactory phenotypic spectrum in idiopathic hypogonadotropic hypogonadism: pathophysiological and genetic implications.

CONTEXT: The olfactory phenotype in patients with idiopathic hypogonadotropic hypogonadism (IHH) ranges from complete anosmia (Kallmann syndrome) to normosmia (normosmic IHH). However, the true prevalence of intermediary olfactory phenotypes (hyposmia) in IHH patients has not yet been assessed, and systematic correlations with anatomical and genetic abnormalities have not been reported. OBJECTIVE: The objective of this study was to evaluate olfactory function in a large IHH cohort and correlate these findings with olfactory magnetic resonance imaging (MRI) and underlying genetic etiology. DESIGN AND SETTING: We conducted a cross-sectional case-control study at an academic referral center. PATIENTS: A total of 286 IHH patients (201 males and 85 females) and 2183 healthy historic controls (1011 males and 1172 females) were studied. MAIN OUTCOME MEASURES: We measured olfactory function using the University of Pennsylvania Smell Identification Test; in 208 subjects, the genetic etiology of IHH was ascertained by DNA sequencing; in a minor subset [39 of 286 subjects (13%)], olfactory structures were determined by MRI. RESULTS: In the IHH cohort, 31.5% were anosmic, 33.6% were hyposmic, and 34.9% were normosmic. Most hyposmic (seven of 11) subjects with MRI data exhibited olfactory structure abnormalities. Of hyposmic subjects, 39.5% harbored mutations in genes involved in either GnRH neuronal migration or GnRH secretion. CONCLUSIONS: IHH subjects display a broad spectrum of olfactory function, with a significant hyposmic phenotype in nearly one third of subjects. The hyposmic subjects harbor mutations in genes affecting GnRH neuronal migration and its secretion, suggesting a pathophysiological overlap between Kallmann syndrome and normosmic IHH. Accurate olfactory phenotyping in IHH subjects will inform the pathophysiology of this condition and guide genetic testing.

Expanding the phenotype and genotype of female GnRH deficiency.

CONTEXT: GnRH deficiency is a rare genetic disorder of absent or partial pubertal development. The clinical and genetic characteristics of GnRH-deficient women have not been well-described. OBJECTIVE: To determine the phenotypic and genotypic spectrum of a large series of GnRH-deficient women. DESIGN, SETTING, AND SUBJECTS: Retrospective study of 248 females with GnRH deficiency evaluated at an academic medical center between 1980 and 2010. MAIN OUTCOME MEASURES: Clinical presentation, baseline endogenous GnRH secretory activity, and DNA sequence variants in 11 genes associated with GnRH deficiency. RESULTS: Eighty-eight percent had undergone pubarche, 51% had spontaneous thelarche, and 10% had 1-2 menses. Women with spontaneous thelarche were more likely to demonstrate normal pubarche (P = 0.04). In 27% of women, neuroendocrine studies demonstrated evidence of some endogenous GnRH secretory activity. Thirty-six percent (a large excess relative to controls) harbored a rare sequence variant in a gene associated with GnRH deficiency (87% heterozygous and 13% biallelic), with variants in FGFR1 (15%), GNRHR (6.6%), and PROKR2 (6.6%) being most prevalent. One woman had a biallelic variant in the X-linked gene, KAL1, and nine women had heterozygous variants. CONCLUSIONS: The clinical presentation of female GnRH deficiency varies from primary amenorrhea and absence of any secondary sexual characteristics to spontaneous breast development and occasional menses. In this cohort, rare sequence variants were present in all of the known genes associated with GnRH deficiency, including the novel identification of GnRH-deficient women with KAL1 variants. The pathogenic mechanism through which KAL1 variants disrupt female reproductive development requires further investigation.

TAC3/TACR3 mutations reveal preferential activation of gonadotropin-releasing hormone release by neurokinin B in neonatal life followed by reversal in adulthood.

CONTEXT: Mutations in TAC3 and TACR3 (encoding neurokinin B and its receptor) have been identified in Turkish patients with idiopathic hypogonadotropic hypogonadism (IHH), but broader populations have not yet been tested and genotype-phenotype correlations have not been established. OBJECTIVE: A broad cohort of normosmic IHH probands was screened for mutations in TAC3/TACR3 to evaluate the prevalence of such mutations and define the genotype/phenotype relationships. DESIGN AND SETTING: The study consisted of sequencing of TAC3/TACR3, in vitro functional assays, and neuroendocrine phenotyping conducted in tertiary care centers worldwide. PATIENTS OR OTHER PARTICIPANTS: 345 probands, 18 family members, and 292 controls were studied. INTERVENTION: Reproductive phenotypes throughout reproductive life and before and after therapy were examined. MAIN OUTCOME MEASURE: Rare sequence variants in TAC3/TACR3 were detected. RESULTS: In TACR3, 19 probands harbored 13 distinct coding sequence rare nucleotide variants [three nonsense mutations, six nonsynonymous, four synonymous (one predicted to affect splicing)]. In TAC3, one homozygous single base pair deletion was identified, resulting in complete loss of the neurokinin B decapeptide. Phenotypic information was available on 16 males and seven females with coding sequence variants in TACR3/TAC3. Of the 16 males, 15 had microphallus; none of the females had spontaneous thelarche. Seven of the 16 males and five of the seven females were assessed after discontinuation of therapy; six of the seven males and four of the five females demonstrated evidence for reversibility of their hypogonadotropism. CONCLUSIONS: Mutations in the neurokinin B pathway are relatively common as causes of hypogonadism. Although the neurokinin B pathway appears essential during early sexual development, its importance in sustaining the integrity of the hypothalamic-pituitary-gonadal axis appears attenuated over time.

Impaired fibroblast growth factor receptor 1 signaling as a cause of normosmic idiopathic hypogonadotropic hypogonadism.

CONTEXT: FGFR1 mutations have been identified in about 10% of patients with Kallmann syndrome. Recently cases of idiopathic hypogonadotropic hypogonadism (IHH) with a normal sense of smell (nIHH) have been reported. AIMS: The objective of the study was to define the frequency of FGFR1 mutations in a large cohort of nIHH, delineate the spectrum of reproductive phenotypes, assess functionality of the FGFR1 mutant alleles in vitro, and investigate genotype-phenotype relationships. DESIGN: FGFR1 sequencing of 134 well-characterized nIHH patients (112 men and 22 women) and 270 healthy controls was performed. The impact of the identified mutations on FGFR1 function was assessed using structural prediction and in vitro studies. RESULTS: Nine nIHH subjects (five males and four females; 7%) harbor a heterozygous mutation in FGFR1 and exhibit a wide spectrum of pubertal development, ranging from absent puberty to reversal of IHH in both sexes. All mutations impair receptor function. The Y99C, Y228D, and I239T mutants impair the tertiary folding, resulting in incomplete glycosylation and reduced cell surface expression. The R250Q mutant reduces receptor affinity for FGF. The K618N, A671P, and Q680X mutants impair tyrosine kinase activity. However, the degree of functional impairment of the mutant receptors did not always correlate with the reproductive phenotype, and variable expressivity of the disease was noted within family members carrying the same FGFR1 mutation. These discrepancies were partially explained by additional mutations in known IHH loci. CONCLUSIONS: Loss-of-function mutations in FGFR1 underlie 7% of nIHH with different degrees of impairment in vitro. These mutations act in concert with other gene defects in several cases, consistent with oligogenicity.

Mutations in fibroblast growth factor receptor 1 cause both Kallmann syndrome and normosmic idiopathic hypogonadotropic hypogonadism.

Mutations in KAL1 and FGFR1 cause Kallmann syndrome (KS), whereas mutations in the GNRHR and GPR54 genes cause idiopathic hypogonadotropic hypogonadism with normal olfaction (nIHH). Mixed pedigrees containing both KS and nIHH have also been described; however, the genetic cause of these rare cases is unknown. We examined the FGFR1 gene in seven nIHH subjects who either belonged to a mixed pedigree (n = 5) or who had associated midline defects (n = 2). Heterozygous FGFR1 mutations were found in three of seven unrelated nIHH probands with normal MRI of the olfactory system: (i) G237S in an nIHH female and a KS brother; (ii) (P722H and N724K) in an nIHH male missing two teeth and his mother with isolated hyposmia; and (iii) Q680X in a nIHH male with cleft lip/palate and missing teeth, his brother with nIHH, and his father with delayed puberty. We show that these mutations lead to receptor loss-of-function. The Q680X leads to an inactive FGFR1, which lacks a major portion of the tyrosine kinase domain (TKD). The G237S mutation inhibits proper folding of D2 of the FGFR1 and likely leads to the loss of cell-surface expression of FGFR1. In contrast, the (P722H and N724K) double mutation causes structural perturbations in TKD, reducing the catalytic activity of TKD. We conclude that loss-of-function mutations in FGFR1 cause nIHH with normal MRI of the olfactory system. These mutations also account for some of the mixed pedigrees, thus challenging the current idea that KS and nIHH are distinct entities.

Strength training in older women: early and late changes in whole muscle and single cells.

In order to examine the relative contribution of neural- and muscle-based adaptation to strength training, we studied early (2 weeks) and later (12 weeks) effects of strength training on muscle size and strength and type I single-fiber size and contractility in 14 elderly women (aged 68-79 years) and seven young controls. Older subjects were randomized to training (n = 7) or control (n = 7) groups. Strength did not change, but whole muscle size increased significantly after 2 weeks. After 12 weeks, strength, whole muscle size, and specific force all increased. No changes occurred in the control group. In single fibers, no changes in size and contractility were noted after 2 weeks, but specific force was higher in the training group after 12 weeks. Early adaptations to strength training in elderly women cannot be attributed to changes at the cellular level and therefore occur primarily in the central nervous system. Later, cellular adaptations in specific force track closely whole muscle changes.