Tuesday, 31 January 2012


Testicular size is determined by palpation and comparison to testis-shaped models of defined sizes (Prader orchidometer).

What is the most reliable sign for the onset of puberty in males?
What is the clinical significance of megalotestis (macroorchidism)?

The answers are provided below as comments.

This page was last updated in February 2012.


  1. *
    The prepubertal testis is about 2 mL in volume with puberty taken to begin when a volume of around 4 mL is attained. As a general rule, a unilateral increase of testicular volume to ≥3 mL is the most reliable sign for the onset of puberty.

    1- An unduly large and asymmetrical testis may indicate testicular tumour and ultrasonography examination of the scrotal contents is mandatory to confirm or exclude the presence of a testicular tumour.

    2- False estimation of testicular volume may occur if there is hydrocele.

    3- Symmetrical large testes (testicular volume of more than 25** – 35 mL each) is either an occasional normal finding (In a study** individuals with bilateral megalotestes had higher sperm counts and better sperm morphology and motility than the controls with normal testicular volumes), or it may be a feature of the fragile X syndrome.


    ** Meschede D, Behre HM, Nieschlag E: Endocrine and spermatological characteristics of 135 patients with bilateral megalotestis. Andrologia 1995; 27:207-212.

  2. Note that:

    The fragile X (familial) mental retardation protein (FMRP) is essential for normal cognitive development and female reproductive function and the fragile X chromosome mental retardation of the fragile X syndrome is caused by absence of FMRP encoded by the fragile X (familial) mental retardation (FMR) 1 gene. In other words, mutations of the gene lead to fragile X syndrome. Blocking the production of the FMRP is caused by expansion of the number of triplet repeat sequences in the FMR1 gene. The nucleobases involved are cytosine (C) and guanine (G) and the repeated sequence is CGG. In the most common form of the condition, the CGG sequence is repeated more than 200 times and it is the abnormal methylation of the expanded repeat that results in silencing of the FMR1 gene (inactivation of the gene), which encodes the FMRP.

    Actually, the number of repeats determines the phenotype. Normally there are less than 50 CGG repeats. And as stated above in the most common form of the condition, there are more than 200 CGG repeats (full mutation), the greater the number of abnormal repetitions found, the more likely the patient will have symptoms. If there are from around 50 to 200 CGG repeats this is called premutation. The premutation does not impair intelligence but the patient may develop the fragile X-associated tremor/ataxia syndrome. During oogenesis, but not during spermatogenesis, the premutation may expand to form the full mutation (on mother transmission of the X chromosome to her children, but not on father transmission of the X chromosome to his daughters as the expansion in length of the FMR-1 gene does not usually occur in X-sperm, maternal genomic imprinting – some describe the maternal genomic imprinting as an early postzygotic event where expansion to the full mutation occurs, also “problems are more common in females if the full mutation is inherited from the mother”). The fragile X syndrome increases in severity down the generations of an affected family (genetic anticipation).

    Examination of the karyotype reveals a constriction at the end of the long arm of the X chromosome, followed by a thin strand of genetic material. The constriction and thin strand give the appearance of a fragile portion of the X chromosome. Sequencing of the genetic material reveals a repeating base pair triplet that is responsible for the syndrome.

    Males are more commonly affected than females (this can explain the male excess in mental institutions and it is actually the most common sex-linked cause of mental retardation). Fragile X syndrome is inherited in an X-linked pattern (complex) and does not always cause clinical symptoms and it does not follow the usual pattern of inheritance for an X linked condition. Patients have physical, cognitive and behavioural abnormalities. The ears might be large (macrotia). The joints may be hyperextensible. Others features include e.g. mitral valve prolapse. The macroorchidism, often becomes manifest just prior to puberty and it shows normal gonadal function. The testes are enlarged in all dimensions, possibly due to prenatal lymphangiectasis. It is not uncommon to see testicular volume > 40 mL. Affected females are typically less mentally impaired than males but in addition they may experience menopause in their mid-30s.


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Main Works of Reference List (The first eight are my top favourites)

  • British National Formulary
  • British National Formulary for Children
  • Guidelines (BAD - BASHH - BHIVA - Uroweb)
  • Oxford Handbook of Genitourinary Medicine, HIV, and Sexual Health
  • Oxford Handbook of Medical Dermatology
  • Rook's Textbook of Dermatology
  • Simple Skin Surgery
  • Weedon's Skin Pathology
  • A Concise Atlas of Dermatopathology (P Mckee)
  • Andrews' Diseases of the Skin
  • Andrology (Nieschlag E FRCP, Behre M and Nieschlag S)
  • Bailey and Love's Short Practice of Surgery
  • Davidson's Essentials of Medicine
  • Davidson's Principles and Practice of Medicine
  • Fitzpatrick's Colour Atlas and Synopsis of Clinical Dermatology (Klaus Wolff FRCP and Richard Allen Johnson)
  • Fitzpatrick’s Dermatology in General Medicine
  • Ganong's Review of Medical Physiology
  • Gray's Anatomy
  • Hamilton Bailey's Demonstrations of Physical Signs in Clinical Surgery
  • Hutchison's Clinical Methods
  • Lever's Histopathology of the Skin
  • Lever's Histopathology of the Skin (Atlas and Synopsis)
  • Macleod's Clinical Examination
  • Martindale: The Complete Drug Reference
  • Oxford Handbook of Clinical Examination and Practical Skills
  • Oxford Textbook of Medicine
  • Practical Dermatopathology (R Rapini)
  • Sexually Transmitted Diseases (Holmes K et al)
  • Statistics in Clinical Practice (D Coggon FRCP)
  • Stockley's Drug Interactions
  • Treatment of Skin Disease: Comprehensive Therapeutic Strategies
  • Yen & Jaffe's Reproductive Endocrinology