A case of 49,XXXYY followed-up from infancy to adulthood with review of literature

Abstract

49,XXXYY is an extremely rare sex chromosomal aneuploidy (SCA), with only seven cases reported worldwide to date. Among these cases, only three have been documented into adulthood. Moreover, no cases of 49,XXXYY have been reported in Japan. This SCA has been identified in two scenarios: in vitro fertilization and abortion. Similar to 47,XXY, this aneuploidy is a type of Klinefelter syndrome. Aneuploidy of the X chromosome can lead to various progressive complications due to excess X chromosomes. Herein, we present the case of a Japanese man with 49,XXXYY. He exhibited developmental delays and external genitalia abnormalities since early infancy but was not closely monitored for these symptoms until the age of 3 years old. At that time, a chromosome test revealed his karyotype to be 49,XXXYY. Subsequent examinations were conducted due to various symptoms, including delayed motor development, intellectual disability, facial dysmorphisms, forearm deformities, hip dysplasia, cryptorchidism, micropenis, primary hypogonadism, and essential tremor. Since reaching puberty, he has undergone testosterone replacement therapy for primary hypogonadism, experiencing no complications related to androgen deficiency to date. He has maintained normal lipid and glucose metabolism, as well as bone density, for a prolonged period. There are no other reports on the long-term effects of testosterone treatment for the SCA. Appropriate testosterone replacement therapy is recommended for individuals with 49,XXXYY to prevent complications. This report will contribute to an enhanced understanding of the 49,XXXYY phenotype, aiding in the diagnosis, treatment, and genetic counseling of future cases.

49,XXXYY is an extremely rare sex chromosomal aneuploidy (SCA). The first case was reported in 1963 in a young man with intellectual disability and Klinefelter syndrome (KS)-like symptoms [1]. To the best of our knowledge, only seven patients with this karyotype have been reported worldwide (Table 1) [1-7]. To date, there are no known cases of this disorder in Japan. A case of 48,XXYY/49,XXXYY mosaic karyotype [8] and another of a fetus terminated after prenatal diagnosis have also been reported [9]. 49,XXXYY is a type of KS [4].

Table 1

Clinical findings of our patient and other patients with 49,XXXYY

Case	Case 1 [1]	Case 2 [2]	Case 3 [3]	Case 4 [4]	Case 5 [5]	Case 6 [6]	Case 7 [7]	Our patient	Reference range
Age at examination	26y	1y9m	42y	15y	3y6m	25y	1y7m	29y
Height (cm)	199.04	80	170	160	NR	182.5	73	180.8
Weight (kg)	119.748	11.8	NR	54	NR	99.8	11.3	80.8
LH (mIU/mL)	NR	NR	NR	NR	NR	16	NR	27.58	0.79–5.72
FSH (mIU/mL)	NR	NR	NR	NR	NR	13	NR	39.2	2.00–8.30
T (ng/dL)	NR	NR	NR	NR	NR	31.9	NR	68	280–800
Testes	Small	Small	Cryptorchidism	Small	Cryptorchidism	Small	Cryptorchidism	Cryptorchidism
Penis	Micropenis	Micropenis	Normal	Micropenis	NR	Micropenis	Micropenis	Micropenis
Facial dysmorphisms	Yes	Yes	Yes	Yes	NR	Yes	Yes	Yes
Forearm deformities	NR	Yes	NR	NR	NR	NR	Yes	Yes
Essential tremor	NR	NR	Yes	NR	NR	NR	NR	Yes
Intellectual Disability	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Maternal age at birth	20y	30y	41y	<25y	NR	31y	25y	21y
Paternal age at birth	NR	35y	40y	<25y	<30y	32y	28y	21y

LH, luteinizing hormone; FSH, follicle-stimulating hormone; T, testosterone; NR, not reported; y, year; m, month

Harry F. Klinefelter first described KS in 1942 as an endocrine disorder characterized by testicular dysgenesis, gynecomastia, hypogonadism, increased LH and FSH secretion, and developmental delay [10, 11]. KS is a chromosomal abnormality in which at least one extra X chromosome is present alongside the normal male karyotype, 46,XY [6]. Most patients with KS have the 47,XXY karyotype, whereas others may exhibit higher-grade aneuploidies (HGAs: 48,XXXY, 48,XXYY, 49,XXYYY, 49,XXXYY, and 49,XXXXY), 46,XY/47,XXY mosaicism, or structurally abnormal X chromosomes [11]. KS is the most common SCA in men. The typical KS karyotype is 47,XXY, with a prevalence of approximately 1 in 500–600 male pregnancies. Furthermore, KS is a relatively common cause of male infertility [12, 13]. The 47,XXY condition is rarely recognized in childhood or adolescence, and most patients remain undiagnosed. Some cases are diagnosed in childhood upon close examination of speech delays or abnormal behavior patterns, whereas others are diagnosed in adolescence during infertility examinations. Approximately 75% of cases remain undiagnosed [12-15]. On the other hand, the karyotype 49,XXXYY, similar to other HGAs, exhibits more severe and varied manifestations than 47,XXY. Intellectual disability is almost inevitable in 49,XXXYY, and many cases are diagnosed in childhood [1-7]. Patients with 49,XXXYY often exhibit facial dysmorphisms, hip dysplasia, skeletal malformation, autism spectrum disorder, impulsivity, and social-emotional problems [1-7].

In patients with 49,XXXYY, as in 47,XXY, appropriate testosterone therapy for gonadal dysfunction is recommended to reduce the patient’s risk of complications and improve long-term prognosis. However, to date, only one report on 49,XXXYY describes LH, FSH, or testosterone measurements as well as testosterone therapy [6].

This SCA is extremely rare, with only three documented cases, showing the course of patients with this karyotype into adulthood [1, 3, 6]. Our case report will contribute to the diagnosis, treatment, and genetic counseling of future cases. Herein, we present the case of a man with 49,XXXYY who has been followed-up from infancy to adulthood.

Case Report

The patient is the first child of Japanese nonconsanguineous parents. The pregnancy and delivery were uneventful, and the patient was born via spontaneous delivery at 37 weeks and 3 days of gestation, with an Apgar score of 10 at 1 min. His birth weight was 2,570 g (–0.98 SD) and length was 45.5 cm (–1.62 SD). Although his parents were intellectually intact, an uncle related to his father had intellectual disability. There was no other family history of intellectual disability or endocrine disorder. At the 2-month infant screening, a micropenis was observed. At 5 months, he was diagnosed with acetabular dysplasia. At the 8-month infant screening, hypotonia was noted, and he could not turn over or sit up. However, a detailed examination was not conducted at that time. Strabismus was diagnosed at the age of 1 year. He started walking at 1 year and 6 months and began speaking words at 2 years. Upon hospitalization at the age of 3 years due to bronchial asthma, congenital conditions such as Prader–Willi syndrome (PWS) were suspected and various symptoms, such as developmental delay, hypotonia, micropenis, cryptorchidism, and strabismus were noted. After obtaining informed consent from his parents, his chromosomes were examined via fluorescence in situ hybridization (FISH) for PWS and the G-string method. No PWS deletion was observed in FISH. The patient’s chromosome karyotype was 49,XXXYY (Fig. 1), leading to a referral to our hospital for further testing. Chromosome tests were not conducted for the parents. His sister, born 5 years after his definitive diagnosis, exhibited a normal phenotype.

Fig. 1

Chromosomal analysis (G-banding). The red arrows indicate multiple sex chromosomes.

At his initial visit to our hospital, his height was 90.4 cm (–1.02 SD) and weight was 14 kg (–0.22 SD) (Fig. 2). Although he could speak a few words, he struggled to formulate sentences. Notably, he exhibited facial dysmorphisms including strabismus, narrow eyelid fissures, and prognathism. Additionally, he presented with a micropenis (penile length, 1.5 cm), left cryptorchidism, and a small right testis (<1 mL). His LH and FSH levels were below sensitivity and elevated, respectively (Table 2). At 5 years, both testes had correctly descended, with a volume of 2 mL each and a penile length of 2.5 cm. His FSH level further elevated, indicating primary hypogonadism (Table 2). At 6 years and 1 month, an intelligence test revealed an intelligence quotient (IQ) of 55. Despite entering a local elementary school, he struggled to keep up with his studies and faced emotional problems such as tantrums, aggression, irritability, seldom smiling, and a stern facial expression. In the fifth grade, he began attending special support classes, managing to read easy words and add single digits. At 10 years and 3 months, an intelligence test revealed an IQ of 50. From the age of 12 years, he began complaining of limited elbow extension and occasional pain. Thus, he was referred to an orthopedic surgeon, who noted mild elbow deformity and kept him under observation (Fig. 3). Persistently high LH and FSH levels (Table 2) led to suspicion of primary hypogonadism, and a human chorionic gonadotropin (hCG) loading test was conducted at 14 years and 8 months. His testosterone response was poor, with basal and peak testosterone levels at 107.1 ng/dL and 117.9 ng/dL, respectively. At 15 years and 7 months, his lumbar spine bone density decreased to 0.739 g/cm² (–2.15 SD), prompting treatment with 12.5 mg testosterone once monthly (Fig. 2). Gynecomastia was observed at around 16 years and 10 months but did not progress significantly. At 21years, testosterone treatment was discontinued due to undeniable side effects, particularly tremors, which had developed at the age of 20 years. The tremors did not improve during withdrawal, and because tremor is also a symptom of KS, testosterone therapy was resumed 6 months later. The patient’s height peaked at 23 years. Currently, at 29 years old, his height and weight are 180.8 cm and 80.9 kg, respectively, with a body mass index of 24.7 kg/m². His bone mineral density has remained normal (Table 3). Recent blood glucose and hemoglobin A1c levels were normal, 108 mg/dL and 5.8%, respectively. A recent chest radiograph showed no cardiac enlargement. Because of his intellectual disability, respiratory function tests have not been performed, but his respiratory symptoms remain stable. He resides with his family, engaging in light labor during the day. Experiencing mood swings, he lives without major problems and receives testosterone treatment at a local hospital, with no other endocrine, cardiovascular, or physical complications.

Fig. 2

Growth chart of the patient.

Table 2

Change in the laboratory data of the case

	3y1m	5y0m	12y8m	14y7m	15y6m	16y3m	19y7m	20y1m	25y7m	28y6m
LH (mIU/mL)	<0.5	2.49	18.39	28.49	27.58	28.48	28.09	31.93	28.67	28.95
(Reference range)	(0.1–3.1)	(0.2–1.2)	(0.2–12.4)	(0.2–7.8)		(0.79–5.72)
FSH (mIU/mL)	7.64	12.53	45.49	38.16	39.2	43.69	60.34	59.95	52.54	39.24
(Reference range)	(0.4–5.2)	(0.7–3.0)	(2.6–10.1)	(0.3–18.4)		(2.00–8.30)
T (ng/dL)	10.4	7.9	41.8	84.3	68	99	190	321	338	183
(Reference range)	(3–32)		(3–68)	(28–1,110)		(280–800)
TG (mg/dL)	—	—	—	53	81	113	110	67	144	128
TC (mg/dL)	—	—	117	110	121	123	129	128	110	155

LH, luteinizing hormone; FSH, follicle-stimulating hormone; T, testosterone; TG, triglycerides; TC, total cholesterol

Fig. 3

Radiographs of the patient. (A) Anteroposterior (AP) and lateral radiograph of the left elbow. (B) AP and lateral radiographs of the right elbow. Various deformities of the bilateral distal humerus were observed (arrows).

Table 3

Change in the bone mineral density of the case

	15y7m	21y4m	28y6m
BMD (L2–4) (g/cm2)	0.739	0.861	0.89
YAM (%)	—	83	85

BMD, bone mineral density; YAM, Young adult mean

Discussion

This is the first Japanese case of 49,XXXYY, an extremely rare SCA. We have closely followed-up the clinical course of this patient into adulthood. Through appropriate testosterone therapy, he has not experienced any systemic complications associated with androgen deficiency. To date, only one report on 49,XXXYY describes LH, FSH, or testosterone measurements as well as testosterone therapy [6]. We report the long-term effects of testosterone therapy on this aneuploidy.

This aneuploidy is classified as KS [4]. Sex chromosome number aberrations in KS are often random events caused by nondisjunction during meiotic divisions that occur paternally or maternally in germ cell development [11, 12, 16]. 49,XXXYY is believed to be caused by one of the following mechanisms: the fertilization of a normal ovum with one X by an XXYY sperm, the fertilization of an XX ovum by an XYY sperm, or the fertilization of an XXX ovum by a YY sperm. For each polysomy possibility, at least two independent nondisjunctions must be assumed, and at least one nondisjunction must be of paternal origin [7, 9]. Sex chromosomal hyperploidy is more common in spermatozoa from patients with KS than in spermatozoa from normal patients. Thus, men with this syndrome may pass on chromosomal abnormalities to their offspring [11]. Because the parents of the patient in this report did not undergo chromosome testing, SCA cannot be ruled out for his father. However, it is unlikely that this patient’s father has SCA, as his parents had two children born by natural conception. While the number of successful pregnancies with the partners of men with KS is increasing, these are usually achieved by in vitro fertilization [17, 18]. It is difficult for the partners of men with KS to experience natural pregnancies.

The impact of parents’ age on the occurrence of KS remains controversial. Some previous reports have suggested that aneuploidy is more likely to occur when parents are older due to an increased tendency for nonsegregation during the first meiosis [19, 20]. Conversely, other reports have indicated that older parents do not increase the risk of having an affected child [11, 21]. There are also reports suggesting that age is not a risk factor for sperm aneuploidy [11, 22, 23]. Some reports have indicated that increased maternal age exerts a weaker effect on KS than on other chromosomal abnormalities [12]. The mechanisms of sex chromosome nondisjunction are diverse, associated some with aberrant recombination, some with increased parental age, and others not [16]. Parental age varied in previous reports of 49,XXXYY, with only one case in their 40s (Table 1) [1-7].

The presence of noninactivated extra genes on the X chromosome is responsible for the genetic background of the KS phenotype. Other possible genetic mechanisms include quantitative chromosome imbalance [24]. In the somatic cells of patients with KS, extra X chromosomes are believed to be inactivated. Therefore, the phenotypic implications of increased KS gene dosage only apply to genes that have escaped X-chromosome inactivation. The KS phenotype progressively worsens with the numerical severity of polysomy [25]. Spaziani et al. recently reported that the increase in the number of extra-Xs is associated with a “dose-dependent” progressive impairment of various complications [26]. This study showed that an increase in extra-Xs leads to an adverse impact on glucose and lipid homeostasis and cardiac and testicular functions [26]. The Short-stature homeobox-containing gene (SHOX) is a noninactivation extra gene affecting the KS phenotype [24]. SHOX haploinsufficiency causes growth retardation and bone changes in Turner syndrome and Leri–Weill chondrodysplasia [27, 28]. Excess SHOX has also been implicated in the growth promotion of KS [29]. Fibroblast growth factor receptor 3 is a transcriptional target of SHOX [30]. This may explain the contribution of SHOX to linear growth and skeletal problems in KS. In a recent case of 49,XXXYY, as in our case, acetabular dysplasia, facial morphology abnormalities, and bony deformity of the forearm were observed [7]. This is not commonly reported in 47,XXY and may be attributed to an additional number of the X chromosome.

Because of androgen deficiency, patients with KS are three times more likely to develop type 2 diabetes than normal men. Androgen deficiency also causes osteoporosis and reduced muscle strength [12, 15]. The average life expectancy of patients with KS is 11.5 years shorter than that of an average male [31]. Serum testosterone levels increase during early puberty in some patients and then start declining by the age of 15 years, becoming lower than normal in approximately 80% of adult patients with 47,XXY [11, 32]. Therefore, even if testosterone levels increase during puberty, long-term testosterone monitoring is still warranted. Early detection and hormonal treatment of androgen deficiency are crucial for improving the life expectancy of patients with KS [11]. Studies have demonstrated that testosterone exerts beneficial effects on the cardiovascular system of men with chronic stable angina and chronic heart failure [11, 33, 34]. Testosterone replacement therapy has been shown to reduce mortality rates from 5.4% to 3.3% in typically hypogonadal men [14, 35]. However, randomized controlled trials on testosterone therapy in KS are lacking. Testosterone therapy is recommended for patients with clinical symptoms and serum levels below normal. In most patients, clinical symptoms appear between the ages of 20 and 30 years [14, 36, 37]. Our patient’s testosterone level gradually increased until the age of 15 years but began to decline from 15 years and 6 months. His response to the hCG challenge test was poor; thus, testosterone replacement therapy was initiated at 15 years and 7 months (Table 2). He has been consistently receiving appropriate testosterone replacement therapy and has not developed any endocrine, cardiovascular, or other physical complications. He has maintained normal lipid and glucose metabolism, bone density, and respiratory function for a prolonged period. In this SCA, as in 47,XXY, appropriate testosterone therapy for gonadal dysfunction is crucial to reduce the patient’s risk of cardiovascular complications and improve long-term prognosis.

In many countries, including Japan, sex chromosome analysis is not included in noninvasive prenatal testing (NIPT) screening [12, 38]. This exclusion is attributed to various reasons, including concerns about the potential for sex selection [12, 39]. The accuracy of NIPT for SCA varies and has been reported to be less reliable than NIPT for autosomal disorders [39]. However, NIPT has contributed to higher rates of prenatal SCA diagnosis in some countries. Howard-Bath et al. reported a significant increase (from 0.95% in 2010 to 2.93% in 2016) in the percentage of SCA cases diagnosed prenatally. Among confirmed fetal SCAs, while maternal advanced age was the most common indication for testing (63%) in 1986, high-risk NIPT accounted for 49% in 2016 [40]. The anticipated increase in detected SCA cases emphasizes the need for comprehensive longitudinal data on the phenotypes of patients prenatally diagnosed with SCA.

There are no other reports on this SCA demonstrating the long-term effects of testosterone treatment. Appropriate testosterone replacement therapy is recommended for individuals with this SCA to prevent complications. This report contributes to an enhanced understanding of the 49,XXXYY phenotype and proves beneficial in the diagnosis, treatment, and genetic counseling of future cases.

Conclusion

Patients with 49,XXXYY present with more severe symptoms than those with 47,XXY. For this SCA, as in 47,XXY, appropriate testosterone replacement therapy is essential to prevent complications.

Acknowledgments

We thank the patient and his family for participating in our study. We would also like to thank Eishin Ogawa and Kazuhiro Haginoya for their clinical support.

Author Contributions

All authors helped write and edit the original draft and approved the submitted manuscript. JK diagnosed, treated, and studied the patient and drafted the manuscript. SK and MK helped draft and complete the manuscript. AM, HS, DS, IF, MU, and MK treated the patient and helped draft and complete the manuscript. AK helped prepare and finalize the manuscript.

Conflict of Interest

The authors have no competing interest to declare.

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