Key Differences Between Turner Syndrome and Down Syndrome Explained

Understanding the Differences Between Turner Syndrome and Down Syndrome

Turner syndrome and Down syndrome are two common genetic conditions that affect a person's growth and development. While both result from chromosomal abnormalities, there are distinct differences between Turner syndrome and Down syndrome in terms of causes, symptoms, and how they are treated.

Causes of Turner Syndrome vs. Down Syndrome

The primary cause of Turner syndrome is that all or part of one X chromosome is missing in a female. This leads to total or partial monosomy X.

In contrast, Down syndrome is caused by an extra copy of chromosome 21 (trisomy 21). This extra genetic material alters development and causes the characteristics of Down syndrome.

Genetic Origin of Turner and Down Syndrome

Turner syndrome is not usually inherited but rather occurs spontaneously. In the majority of cases, the missing X chromosome comes from the father during conception.

Down syndrome is also not typically inherited. The extra copy of chromosome 21 occurs due to a random error in cell division during development, causing trisomy 21.

Timing of Origin Differs

The chromosomal abnormality causing Turner syndrome occurs right at conception. The missing X chromosome impacts development from the start.

With Down syndrome, the extra copy of chromosome 21 usually occurs a few weeks after conception during cell division. This delays the effects on initial development.

Turner Syndrome Only Affects Females

Since Turner syndrome is caused by a missing X chromosome, it only occurs in females. Biological males cannot have Turner syndrome.

Down syndrome affects both males and females equally, since the extra chromosome 21 can occur in either sex.

Prevalence Rates Vary

Turner syndrome only occurs in about 1 in 2000 to 1 in 5000 female births.

Down syndrome is more common, affecting around 1 in 700 to 1 in 1000 births of any sex.

Risk Factors Differ

Turner syndrome is not associated with any specific risk factors. It occurs randomly.

However, the risk of having a baby with Down syndrome does increase with the mother's age. The chance is 1 in 1250 for a 20 year old but 1 in 100 for a 40 year old.

Symptoms and Characteristics

While both conditions involve some shared traits like short stature, the symptoms and characteristics of Turner and Down syndrome have some clear differences.

Characteristic Facial Features

Individuals with Down syndrome often have distinct facial features like almond eyes, a flat nasal bridge, small nose and mouth, and upward slanting eyes.

The facial features of Turner syndrome are more subtle and include a broad, flat neck, low-set ears, narrow palate, and drooping eyelids.

Heart Defects Present

About 50% of people with Turner syndrome are born with some type of heart defect or problem with the main blood vessels.

Congenital heart defects also affect around 50% of those with Down syndrome. The defects can involve the walls, valves, or arteries.

Hearing Loss

Recurrent ear infections cause hearing loss in about 30% to 50% of individuals with Turner syndrome.

Hearing problems and deafness also frequently accompany Down syndrome, caused by small or malformed ears.

Growth Differences Are Apparent

Short stature is nearly universal in Turner syndrome, with the majority of adult height under 5 feet.

Newborns with Down syndrome are often average size. However, their growth then slows, leading to shorter height.

Puberty Often Delayed

Delayed, incomplete, or absent puberty is typical in Turner syndrome due to ovarian problems.

Puberty is also usually delayed by 1 to 2 years for teenagers with Down syndrome. But it does eventually occur.

Infertility Is Common

About 95% of women with Turner syndrome experience infertility due to ovarian dysfunction or failure.

Fertility rates are lower in Down syndrome, but not zero. About 30% of males and 50% of females are fertile.

Intellectual Disability Varies

The intellectual disability associated with Turner syndrome ranges from normal intelligence to mild impairment.

Moderate intellectual and learning disability is nearly universal in Down syndrome and is usually more significant.

Thyroid Problems

Thyroid issues occur in over 30% of people with Turner syndrome.

Hypothyroidism is also more common in those with Down syndrome, seen in around 15%.

Increased Leukemia Risk

There is an elevated risk of acute myeloid leukemia and hepatoblastoma cancer in children with Down syndrome.

Turner syndrome itself does not increase cancer risk. However, hormone therapies used sometimes increase likelihood of certain cancers.

Diagnosing Turner vs. Down Syndrome

Accurately diagnosing either syndrome involves analyzing the chromosomes through prenatal or postnatal testing.

Prenatal Diagnostic Testing Options

Prenatal diagnosis includes chorionic villus sampling or amniocentesis to karyotype the fetus's chromosomes.

This detects monosomy X in Turner syndrome and trisomy 21 in Down syndrome about 99% of the time.

Postnatal Diagnosis

After birth, a high-resolution karyotype using a blood sample confirms Turner or Down syndrome in an infant or child.

A cheek swab for fluorescent in situ hybridization (FISH) can also identify missing or extra chromosomes.

Further Testing Assesses Symptoms

Echocardiography, thyroid function tests, ovarian and fertility assessments, hearing tests, and neurological evaluations provide additional information on the associated symptoms and body systems affected.

Early Diagnosis Is Crucial

Early diagnosis and management of both syndromes is vital to improve outcomes and quality of life. Prompt treatment of issues like heart defects, hearing loss, and thyroid dysfunction leads to better long-term health.

Growth Hormones for Turner and Down Syndrome

Growth hormone therapy is used to increase height in both Turner and Down syndrome, but at different ages and doses.

Turner Syndrome Height Therapy

Growth hormones are started at a very young age in Turner syndrome, sometimes under 12 months old, to maximize height.

Doses are higher than typical, designed to add several inches of adult height closer to a normal range for a woman.

Down Syndrome Height Therapy

In Down syndrome, the goal is less about near-normal height and more about reaching one's full potential.

So growth hormones often start around age 2-4 and use typical hormone deficiency doses, adding only 1-3 inches.

Earlier Treatment for Turner Syndrome

Starting growth hormones at age 11-13 helps most with height in Turner syndrome before plates close.

Treatment after age 11 in Down syndrome has little effect on growth plates already slowed by the syndrome.

Turner Syndrome Prioritizes Height

Increasing height in Turner syndrome helps normalize proportions and reduce social stigma of short stature.

With Down syndrome, quality of life is not as closely tied to height, so hormonal therapy focuses on reaching one's natural potential.

Fertility Differences in Turner and Down

Fertility varies greatly between the two conditions due to the impact on reproductive systems.

Puberty Onset Difficulties

Absent or incomplete puberty must be induced for most girls with Turner syndrome because of ovarian failure.

Down syndrome adolescents go through puberty spontaneously, though it is delayed 1-2 years on average.

Estrogen Therapy in Turner Syndrome

Estrogen therapy is given to girls with Turner syndrome to induce feminine body changes absent without ovarian estrogen production.

Estrogen is usually not needed for pubertal development in teens with Down syndrome.

Turner Syndrome Requires Assisted Reproduction

Due to ovarian problems, achieving pregnancy requires in vitro fertilization with donor eggs for women with Turner syndrome.

Those with Down syndrome can conceive spontaneously, though fertility rates are reduced compared to the general population.

Higher Spontaneous Miscarriage Rate

The rate of miscarriage is higher in women with Turner syndrome who achieve pregnancy through IVF.

The miscarriage rate in Down syndrome conceptions is estimated to be around 35%.

Down Syndrome Congenital Heart Risks

Women with Down syndrome pregnant or pursuing pregnancy need careful heart monitoring as pregnancy stresses the cardiovascular system.

Heart conditions related to Turner syndrome do not affect pregnancy, as external eggs and hormones are used.

Lifespan Comparisons

On average, lifespan expectancies are lower for both conditions but significantly more so for Down syndrome.

Reduced Life Expectancy

The expected lifespan for a woman with Turner syndrome is reduced by at least 10 years compared to the general female population.

Down syndrome reduces average life expectancy even more significantly, by 12 to 20 years.

Cardiovascular Issues Reduce Life Span

Heart defects and hypertension contribute to reduced lifespans with Turner syndrome.

Likewise, congenital heart disease is a major cause of shortened lifespan with Down syndrome.

Respiratory Issues Play a Role

Recurrent respiratory infections and breathing problems during sleep reduce the lifespan of people with Down syndrome.

These respiratory problems are less common in Turner syndrome.

Other Health Issues Cause Early Death

Thyroid disease, diabetes, and stroke also contribute to earlier mortality in Down syndrome.

Aortic problems, liver conditions, osteoporosis, obesity, and ear issues impact health and survival with Turner syndrome.

Routine Care Helps Life Expectancy

Ongoing good healthcare improves life expectancy for both conditions. However, gaps in care access for adults with Down syndrome need addressing.

With treatment, many people with Down syndrome now live into their 50s and 60s.

Takeaway on Turner vs. Down Syndrome

While Turner syndrome and Down syndrome share some common symptoms like short stature and heart defects, the two conditions stem from different chromosomal abnormalities and have divergent effects, particularly on fertility. Understanding the differences in causes, growth patterns, associated health issues, and life expectancy between the two syndromes helps inform treatment.

With coordinated medical care, developmental support, and community inclusion, people with both Turner and Down syndromes can thrive and enjoy fuller, more independent lives. However, work remains to ensure adequate care across their lifespans.

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a healthcare professional before starting any new treatment regimen.