Patient's question:
I am already a grown man, but my penis is a bit small, and it's not normal. If it weren't for genetics, because the penises of my ancestors were still quite large, but mine is problematic. What factors or causes could this small penis be?Doctor's answer:
Hello, the causes of micropenis include: ① Hypogonadism due to insufficient secretion of gonadotropins; ② Hypogonadism due to excessive secretion of gonadotropins; ③ Primary micropenis.1. Hypogonadism due to insufficient secretion of gonadotropins
(1) Abnormal brain tissue structure: Children with anencephaly lack hypothalamic secretion function. Even if the pituitary gland develops normally, due to the absence of gonadotropin-releasing hormone (GnRH), testosterone secretion is reduced, leading to micropenis. Congenital pituitary hypoplasia, partial agenesis of the corpus callosum resulting in hypothalamic dysfunction, and cerebellar malformations with occipital encephalocele and motor coordination disorders, among other midline brain development abnormalities, are all caused by insufficient secretion of gonadotropins and result in micropenis. Additionally, they may lead to multiple congenital anomalies in other systems.
(2) Congenital gonadotropin-releasing hormone deficiency without abnormal brain tissue: This factor or cause is more common in causing micropenis compared to the former. The specific etiology is unclear, and it is often associated with various syndromes, such as Kallmann syndrome, Prader-Willi syndrome, and Laurence-Moon-Biedel syndrome. These conditions are often accompanied by multiple congenital anomalies and are believed to be related to chromosomal and genetic abnormalities. There are also cases where endocrine and metabolic abnormalities lead to deficiencies in GnRH, luteinizing hormone (LH), and other hormones.
2. Hypogonadism due to excessive secretion of gonadotropins
In these patients, both the hypothalamus and pituitary gland function normally. However, during the late stages of pregnancy, the testes undergo degenerative changes, leading to reduced testosterone secretion. Through negative feedback mechanisms, this results in excessive secretion of gonadotropins. The factors or causes leading to micropenis are primarily related to the testes themselves, such as congenital absence of the testes or undescended testes. In some cases, the testes may be normal, but the luteinizing hormone (LH) receptor is abnormal, preventing sufficient testosterone secretion. Additionally, it is important to consider any gender abnormalities.
3. Primary micropenis
In addition to the above factors or causes, a small portion of patients have a hypothalamic-pituitary-testicular axis with normal hormone secretion but still have micropenis, which often grows during puberty. The etiology is unclear, but it is speculated that it may be due to delayed gonadotropin stimulation during late embryonic development, transient decreases in testosterone secretion, or other factors. There is also a possibility that some patients may have abnormal androgen receptors. Patients with micropenis may have sex chromosome abnormalities, such as Klinefelter syndrome (47,XXY), poly-X syndrome (48,XXXY and 49,XXXXY), and polysomy (69,XXY trisomy) malformations.