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PubMed This is a summary of 16 peer-reviewed journal articles Updated
Genetics

Symptoms and Warning Signs of 48,XXXY Syndrome

At a Glance

48,XXXY syndrome is a rare genetic condition that causes physical, cognitive, and behavioral symptoms in males. Key signs include forearm bone fusion (radioulnar synostosis), low muscle tone, speech delays, mild to moderate intellectual disability, and low testosterone during puberty.

While every child with 48,XXXY syndrome is unique, the presence of two extra X chromosomes typically leads to a more complex range of symptoms than the more common 47,XXY (Klinefelter syndrome) [1][2]. Doctors often refer to this as a “dose-dependent” effect, where the additional genetic material impacts multiple systems in the body [3].

Physical and Skeletal Manifestations

The physical signs of 48,XXXY can involve the bones, growth patterns, and the reproductive system.

  • Skeletal and Joint Issues: A hallmark of 48,XXXY is radioulnar synostosis, a condition where the two bones in the forearm (the radius and ulna) are fused together at birth [4]. This can limit the child’s ability to rotate their forearms (turning palms up or down) [5]. Other skeletal signs may include clinodactyly (a permanent curving of a finger, usually the pinky) and flat feet [6].
  • Stature and Growth: Boys with 48,XXXY may have altered growth trajectories. While 47,XXY is strongly associated with tall stature, the height increase in 48,XXXY may be less pronounced, and stature is generally more variable due to compounded skeletal issues [7][2].
  • Genital Development: Some infants are born with micropenis (a typically formed but small penis) or cryptorchidism (undescended testes) [8][9].
  • Facial Features: Some children may have mild dysmorphic features, such as an increased distance between the eyes (hypertelorism) or skin folds covering the inner corners of the eyes (epicanthal folds) [6][10].

Neurodevelopmental and Cognitive Symptoms

The cognitive profile of 48,XXXY often requires intensive educational and therapeutic support.

  • Intellectual Disability: Most individuals with 48,XXXY have some degree of intellectual disability, typically ranging from mild to moderate [11][12]. This is often more significant than the learning disabilities seen in classic Klinefelter syndrome [3].
  • Speech and Language: Significant delays in expressive and receptive language are common. Children may struggle to find words or process complex instructions [13].
  • Motor Skills: Hypotonia (low muscle tone) is frequently observed in infancy, which can lead to delays in reaching physical milestones like sitting up, crawling, and walking [14].

Behavioral and Psychiatric Symptoms

Behavioral health is a key focus of long-term care for 48,XXXY.

  • Autism Spectrum Disorder (ASD): There is an increased risk for ASD and other social communication challenges [11]. This may manifest as difficulty reading social cues or a preference for repetitive routines.
  • Executive Dysfunction: Children may struggle with executive function—the mental skills used to manage time, pay attention, and switch focus between tasks [11].
  • Mood and Anxiety: As children reach adolescence and adulthood, they may be more prone to anxiety, depression, or ADHD-like symptoms [15].

Progression Across the Lifespan

Symptoms evolve as a child matures, making regular follow-ups essential.

Stage Common Focus Areas
Infancy Identifying hypotonia, monitoring genital development, and screening for skeletal fusions [14][8].
Childhood Managing speech delays, supporting motor coordination, and evaluating for social/behavioral disorders like ASD [11][13].
Puberty Monitoring for hypogonadism (low testosterone). Many boys will require hormone replacement to support bone health and the development of secondary sex characteristics [2][1].
Adulthood Managing long-term metabolic health, including monitoring for thyroid issues, diabetes risk, and cardiac health [2][3].

Early diagnosis and a multidisciplinary approach—combining genetics, endocrinology, and specialized therapies—are the best ways to manage these symptoms and support your child’s quality of life [1][16].

Common questions in this guide

What physical symptoms are common in babies with 48,XXXY syndrome?
Infants with 48,XXXY syndrome often have low muscle tone (hypotonia) and may be born with genital differences like undescended testicles or a smaller penis. They can also have skeletal issues like radioulnar synostosis, where the forearm bones are fused.
Does 48,XXXY syndrome cause intellectual disability?
Yes, most individuals with 48,XXXY syndrome have mild to moderate intellectual disability. They also frequently experience significant delays in speech and language development, alongside challenges with motor skills and executive function.
Is autism more common in children with 48,XXXY syndrome?
Yes, there is an increased risk for Autism Spectrum Disorder and other social communication challenges in boys with 48,XXXY syndrome. Children may have difficulty interpreting social cues or prefer repetitive, structured routines.
Will my child need hormone therapy for 48,XXXY syndrome?
As boys with 48,XXXY syndrome approach puberty, they commonly experience low testosterone levels, a condition known as hypogonadism. Many will require testosterone replacement therapy to support bone health and the development of adult physical characteristics.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Given the higher risk for radioulnar synostosis, should we get baseline X-rays of my child's forearms?
  2. 2.When should we begin screening for Autism Spectrum Disorder (ASD) and executive function challenges?
  3. 3.How do you plan to monitor my child's thyroid and adrenal function as they grow?
  4. 4.What is the recommended timing for starting testosterone replacement therapy to support pubertal development?
  5. 5.Are there specific physical activities or sports my child should avoid if they have joint or skeletal limitations?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (16)
  1. 1

    A Patient with Moderate Intellectual Disability and 49, XXXYY Karyotype.

    Verhoeven WMA, Egger JIM, Mergler S, et al.

    International journal of general medicine 2022; (15()):2799-2806 doi:10.2147/IJGM.S348844.

    PMID: 35300132
  2. 2

    From Klinefelter Syndrome to High Grade Aneuploidies: Expanding the Gene-dosage Effect of Supernumerary X Chromosomes.

    Spaziani M, Carlomagno F, Tarantino C, et al.

    The Journal of clinical endocrinology and metabolism 2024; (109(8)):e1564-e1573 doi:10.1210/clinem/dgad730.

    PMID: 38193351
  3. 3

    Pseudoautosomal Region 1 Overdosage Affects the Global Transcriptome in iPSCs From Patients With Klinefelter Syndrome and High-Grade X Chromosome Aneuploidies.

    Astro V, Alowaysi M, Fiacco E, et al.

    Frontiers in cell and developmental biology 2021; (9()):801597 doi:10.3389/fcell.2021.801597.

    PMID: 35186953
  4. 4

    Congenital radioulnar synostosis: is prenatal diagnosis possible? - A case report.

    Li YY, Olisova K, Chen YN, et al.

    Taiwanese journal of obstetrics & gynecology 2023; (62(2)):334-335 doi:10.1016/j.tjog.2022.09.011.

    PMID: 36965904
  5. 5

    Clinical, Cognitive and Neurodevelopmental Profile in Tetrasomies and Pentasomies: A Systematic Review.

    Ricciardi G, Cammisa L, Bove R, et al.

    Children (Basel, Switzerland) 2022; (9(11)) doi:10.3390/children9111719.

    PMID: 36360447
  6. 6

    Neonatal diagnosis of 49, XXXXY syndrome.

    Etemadi K, Basir B, Ghahremani S

    Iranian journal of reproductive medicine 2015; (13(3)):181-4.

    PMID: 26000009
  7. 7

    Influences of sex chromosome aneuploidy on height, weight, and body mass index in human childhood and adolescence.

    Hanson C, Blumenthal J, Clasen L, et al.

    American journal of medical genetics. Part A 2024; (194(2)):150-159 doi:10.1002/ajmg.a.63398.

    PMID: 37768018
  8. 8

    [Correlation of micropenis with abnormal chromosomal karyotype in peripheral blood lymphocytes].

    Chen HT, Huang H, Ma H, Li S

    Zhonghua nan ke xue = National journal of andrology 2020; (26(11)):1006-1009.

    PMID: 34898071
  9. 9

    Klinefelter Syndrome: Clinical Spectrum Based on 44 Consecutive Cases from a South Indian Tertiary Care Center.

    Asirvatham AR, Pavithran PV, Pankaj A, et al.

    Indian journal of endocrinology and metabolism 2019; (23(2)):263-266 doi:10.4103/ijem.IJEM_582_18.

    PMID: 31161115
  10. 10

    48, XXXY/49, XXXXY mosaic: new neuroradiological features in an ultra-rare syndrome.

    Milani D, Bonarrigo F, Avignone S, et al.

    Italian journal of pediatrics 2015; (41()):50 doi:10.1186/s13052-015-0156-0.

    PMID: 26168786
  11. 11

    Psychological functioning, brain morphology, and functional neuroimaging in Klinefelter syndrome.

    Skakkebaek A, Gravholt CH, Chang S, et al.

    American journal of medical genetics. Part C, Seminars in medical genetics 2020; (184(2)):506-517 doi:10.1002/ajmg.c.31806.

    PMID: 32468713
  12. 12

    A Rare Case of Klinefelter Syndrome Accompanied by Spastic Paraplegia and Peripheral Neuropathy.

    Sasaki R, Ohta Y, Takahashi Y, et al.

    Internal medicine (Tokyo, Japan) 2019; (58(3)):437-440 doi:10.2169/internalmedicine.1048-18.

    PMID: 30210107
  13. 13

    Effect of sex chromosome number variation on attention-deficit/hyperactivity disorder symptoms, executive function, and processing speed.

    Green T, Flash S, Shankar G, et al.

    Developmental medicine and child neurology 2022; (64(3)):331-339 doi:10.1111/dmcn.15020.

    PMID: 34431088
  14. 14

    [Karyptype 48,XXXY/49,XXXXY and proximal radioulnar synostosis].

    Girón Del Río R, Jeronimo Dos Santos T, Travieso-Suárez L, et al.

    Anales de pediatria 2018; (88(5)):282-284 doi:10.1016/j.anpedi.2017.05.008.

    PMID: 28750730
  15. 15

    Psychological distress in parents of children with autism spectrum disorder: A cross-sectional study based on 683 mother-father dyads.

    Li F, Tang Y, Li F, et al.

    Journal of pediatric nursing 2022; (65()):e49-e55 doi:10.1016/j.pedn.2022.02.006.

    PMID: 35249769
  16. 16

    Down-Klinefelter syndrome (48,XXY,+21) in a neonate associated with congenital heart disease.

    Rodrigues MA, Morgade LF, Dias LFA, et al.

    Genetics and molecular research : GMR 2017; (16(3)) doi:10.4238/gmr16039780.

    PMID: 28973759

This page provides educational information about the symptoms of 48,XXXY syndrome. It is not a substitute for professional medical advice, and you should always consult your pediatric endocrinologist or geneticist regarding your child's care and development.

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